Cockayne Syndrome and the COFS-XP-CS Spectrum

Literature and regulatory information updated: 29 October 2026.

Includes the chromosomal instability and DNA repair disorders and the dermatological and integumentary diseases. Treats as a single class Cockayne syndrome (types I, II and III), cerebro-oculo-facio-skeletal syndrome (COFS) and ultraviolet-sensitive syndrome (UVSS); the xeroderma pigmentosum/Cockayne syndrome complex (XP/CS) is described here in its shared aspects.

0. Reference Summary Table

1. Introduction

1.1. Original description

Edward Alfred Cockayne, a London paediatrician, published in 1936 in the Archives of Disease in Childhood a description of two siblings with “dwarfism with retinal atrophy and deafness” and returned to the subject in 1946, in the same journal, with the follow-up of the patients [22, 23]. The title of both articles summarises the triad that served as the reference for decades: postnatal growth failure, retinal degeneration and hearing loss. Some dysmorphology textbooks date the description to 1946 because they cite only the second article, but the first publication is from 1936 [5, 18]. In 1992, Nance and Berry reviewed 140 published cases and proposed the first formal diagnostic criteria, designed for the classic form [1, 24].

1.2. COFS syndrome and the Manitoba Aboriginal population

In 1974, Pena and Shokeir described in First Nations families of Manitoba, Canada, an autosomal recessive disorder with congenital neurogenic arthrogryposis, microcephaly, microphthalmia, cataracts and brain degeneration of prenatal onset, which they called cerebro-oculo-facio-skeletal syndrome [25, 26]. The name was later applied to a heterogeneous group of children with arthrogryposis and ocular malformations, and the eponym “Pena-Shokeir syndrome type II” became a synonym [1, 2]. In 2000, Meira and colleagues showed that two children with COFS related to that population had a cellular phenotype indistinguishable from that of Cockayne syndrome and were homozygous for the same ERCC6 variant, also present in three other patients of the group; COFS came to be understood as the prenatal form of Cockayne syndrome [1, 27]. In 2008, Laugel and colleagues described three unrelated COFS patients with ERCC6 variants and proposed diagnostic criteria based on genetically confirmed cases, placing COFS at the severe end of the spectrum [28].

1.3. Molecular discovery

The sensitivity of patient cells to UV radiation and the defective recovery of RNA synthesis after irradiation made it possible to define two complementation groups, A and B. The group B gene, ERCC6, was cloned by Troelstra and colleagues in 1992 and identified as a member of a helicase subfamily involved in preferential repair of active genes [29]. In 1995, Henning and colleagues showed that the group A gene, ERCC8, encodes a WD-repeat protein that interacts with CSB and with a subunit of the transcription factor TFIIH [30]. In 1994, Itoh and colleagues described siblings with photosensitivity and biochemical features of Cockayne syndrome but without the systemic manifestations, who did not belong to any known complementation group; in 2012, UVSSA variants were identified in these families, the third transcription-coupled repair gene associated with human disease [4, 31, 32]. The 2010 mutation update compiled 88 ERCC6 and ERCC8 variants in 84 families and created locus-specific databases [33].

1.4. Current nomenclature and classifications

Three classification systems coexist. The first, historical, divides the disease into type I (classic), type II (severe, present at birth) and type III (mild and late), to which COFS is added as the fetal form along with the XP/CS complex; this is the system used by GeneReviews and by Orphanet, which keeps separate codes for the three types [1, 12–14]. The second, proposed by Natale in 2011 on the basis of 45 surveyed patients and literature data, renames the groups as severe, moderate and mild, includes COFS in the severe group and adds a fourth group, “UV sensitivity only/adult onset” [5, 34]. The third, quantitative, is the severity score of Spitz and colleagues (2021), which measures five domains on a 0 to 15 scale and confirmed that the distribution of clinical presentations is continuous [35]. The CoSyNH natural history study (Cockayne Syndrome Natural History) observed phenotypic discordance between siblings and recommends that, when talking to families, classification into types be replaced by descriptive information on morbidity and mortality [18]. The genetic classification distinguishes CS type A (ERCC8, OMIM 216400) and CS type B (ERCC6, OMIM 133540), and COFS in four types according to the gene [1, 6, 9].

1.5. Entities covered in this article

Cockayne syndrome is an autosomal recessive multisystem disorder caused by biallelic ERCC8 or ERCC6 variants, with short stature, a characteristic facial appearance, premature ageing, photosensitivity, progressive neurological dysfunction and intellectual disability [1, 11]. COFS syndrome is the prenatal-onset form, with arthrogryposis, fetal growth restriction, severe congenital microcephaly and congenital cataracts or microphthalmia [1, 28]. UVSS is an autosomal recessive photodermatosis with cutaneous photosensitivity and mild dyspigmentation, without skin cancer, growth failure or neurological disease, caused by ERCC6, ERCC8 or UVSSA variants [15, 36]. The XP/CS complex combines the cutaneous signs of xeroderma pigmentosum, including the risk of skin cancer, with the systemic and neurological signs of Cockayne syndrome, and results from variants in xeroderma pigmentosum genes (ERCC5, ERCC2, ERCC3 and ERCC4) [3, 10]. The forms combined with trichothiodystrophy due to ERCC2 and xeroderma pigmentosum with neurological disease (De Sanctis-Cacchione syndrome) are mentioned here under differential diagnosis.

2. Molecular Genetics and Pathophysiology

2.1. Transcription-coupled nucleotide excision repair

Nucleotide excision repair (NER) removes lesions that distort the double helix, such as UV-induced pyrimidine dimers, by excising the DNA segment containing the damaged bases [36]. The pathway has two recognition branches. Global genome repair (GG-NER) acts on all DNA and is defective in xeroderma pigmentosum and trichothiodystrophy; transcription-coupled repair (TC-NER) preferentially removes lesions on the transcribed strand of active genes, signalled by stalled RNA polymerase II, and is defective in Cockayne syndrome, COFS and UVSS [1, 36]. In Cockayne syndrome GG-NER is preserved, so unscheduled DNA synthesis (UDS) after UV irradiation is broadly normal, whereas recovery of RNA synthesis (RRS) is slow [35, 36].

2.2. ERCC6 and the CSB protein

ERCC6 maps to 10q11.23 (OMIM 609413; MANE (Matched Annotation from NCBI and EMBL-EBI) transcript NM_000124.4) and encodes CSB, a 1493-amino-acid protein with at least seven conserved DNA and RNA helicase domains, belonging to the chromatin remodeller family [1, 6, 37, 38]. CSB is the factor that initiates TC-NER: it recognises and binds RNA polymerase II stalled at a lesion on the transcribed strand and recruits CSA and TFIIH so that the lesion can be excised; it also appears to promote transcription elongation by RNA polymerase II and possibly by polymerases I and III [1, 6]. The PiggyBac transposon PGBD3 has been inserted in intron 5 of ERCC6 for more than 43 million years; alternative splicing of the first five ERCC6 exons to PGBD3 produces a 1061-amino-acid CSB-PGBD3 fusion protein, conserved in primates [38]. In a Han Chinese family, four women from two generations with secondary amenorrhoea were heterozygous for the missense variant p.(Gly746Asp), and among 432 Chinese women with sporadic premature ovarian insufficiency two had heterozygous ERCC6 variants; this autosomal dominant phenotype is defined by secondary amenorrhoea with raised follicle-stimulating hormone before the age of 40 and has not been described in families with Cockayne syndrome [7, 8, 38].

2.3. ERCC8 and the CSA protein

ERCC8 maps to 5q12.1 (OMIM 609412; MANE transcript NM_000082.4) and encodes CSA, a 396-amino-acid protein that is the WD (tryptophan-aspartate) repeat substrate-recognition subunit of a DDB1- and cullin 4-dependent E3 ubiquitin ligase complex; it interacts with CSB and with the p44 subunit of TFIIH [1, 9, 37, 39]. Recruited to stalled RNA polymerase II, CSA ubiquitinates the RPB1 subunit at lysine 1268, a checkpoint for polymerase stability, recruits TFIIH and promotes the ubiquitination and proteasomal degradation of CSB, a step required for the resumption of RNA synthesis after repair [9].

2.4. UVSSA

UVSSA maps to 4p16.3 (OMIM 614632) and encodes a TC-NER scaffold protein that is recruited to stalled RNA polymerase II, brings the deubiquitinase USP7 to the lesion to stabilise CSB, and promotes ubiquitination of RNA polymerase IIo and loading of TFIIH [4, 32]. Biallelic loss abolishes TC-NER and causes UVSS type 3 [4].

2.5. From repair defect to phenotype

TC-NER deficiency explains the cutaneous photosensitivity but not the growth failure or the neurodegeneration, because most patients with xeroderma pigmentosum have combined TC-NER and GG-NER deficiency and yet have normal growth and neurological function [1]. UVSS reinforces the paradox: patients with ERCC6 or ERCC8 variants causing UVSS have a cellular repair defect identical to that of Cockayne syndrome and yet normal growth and development, without microcephaly or premature ageing [18, 36]. Additional functions of the CS proteins have been proposed: restart of transcription after genotoxic stress, through degradation of the ATF3 repressor [1]; repair of oxidative DNA damage, preserved in UVSS cells and defective in CS cells [1, 4]; and mitochondrial metabolism [1]. CoSyNH stressed that none of these processes has yet been shown to produce the phenotype on its own [18].

The most recent model places the fate of stalled RNA polymerase II at the centre. UVSSA-deficient cells clear the stalled polymerase by proteasomal degradation, which leaves alternative repair pathways available, whereas CSB- or CSA-deficient cells do not [40]. In 2026, Gonzalo-Hansen and colleagues studied patients with the early nonsense variant ERCC6 NM_000124.4:c.229C>T p.(Arg77Ter), which, although the protein is undetectable, causes UVSS rather than Cockayne syndrome, and showed that residual functional CSB expression allows degradation of the stalled polymerase [37, 40]. The absence of cancer risk despite the repair defect is attributed to the concurrent deficit in transcription and cell proliferation, and is the theoretical basis of the recommendation against growth hormone [1, 6].

In animal models, CSA- or CSB-deficient mice develop severe renal pathology, with impaired de novo synthesis of nicotinamide adenine dinucleotide (NAD+) owing to persistent ATF3 activation at the locus of the rate-limiting enzyme QPRT, in studies published in 2025 [41]. Fibroblasts from patients with ERCC6 variants show mitochondrial DNA depletion, lower respiratory capacity and collapse of survival under metabolic stress, in a 2026 preprint not yet peer reviewed [42].

2.6. Neuropathology

In all forms, neuropathology shows demyelination with a “tigroid” pattern of the subcortical white matter, multifocal calcium deposition, relative preservation of neurons, absence of senile plaques, amyloid, ubiquitin or tau, and arteriosclerosis [1]. The calcifications seen on imaging correspond to complex mineralisation with coexisting iron [18]. This demyelinating pattern with calcifications contrasts with the primary neuronal degeneration of neurological xeroderma pigmentosum [43].

2.7. Inheritance and variant spectrum

All forms of the spectrum are autosomal recessive and result from loss of function [1]. In the series of 124 patients from four European centres, 39 had ERCC8 variants and 85 ERCC6 variants; most variants were truncating, missense variants clustered in short regions of the proteins, and hotspots and founder variants were identified in ERCC6 [44]. In the 2010 update, 52 of 84 families (62%) had ERCC6 variants [33]. By method, sequencing detects about 90% of pathogenic ERCC6 variants and 88% of ERCC8 variants, and targeted deletion/duplication analysis detects the remaining 10% and 12%; these proportions refer to known variants and are not equivalent to the clinical sensitivity of a test [1]. Pathogenic variants have been described in the non-coding region of ERCC8, including a deep intronic variant in a splicing regulatory element associated with severe disease with long survival [1, 45].

The variants in the table, published on transcripts NM_000124.3 and NM_000082.3, keep the same c. numbering on the MANE transcripts [37].

Laugel's 2013 review, which compiled more than 120 genetically confirmed patients (78 different variants in ERCC6 and 30 in ERCC8), showed that most families have private variants but identified founder effects in specific populations, including an ERCC8 variant in Portuguese and Brazilian patients [49]. In ERCC8, all missense variants lie in the WD motifs, half of them in the fourth; in ERCC6, missense variants and in-frame deletions lie in the two RecA-like domains, with four missense variants clustered between residues 670 and 687 of helicase motif III [49].

The review also describes, without full c. notation, the ERCC8 variant p.Asp93LeufsTer26 (published designation, with no confirmed c. mapping on NM_000082.4) in Japanese families and a deletion in the 5′ untranslated region of ERCC6 specific to Réunion Island [49]. The c. notations and genomic coordinates in the table were normalised in VariantValidator; for splicing variants, the protein effect is the one described in the publication from RNA studies, and the normalised prediction is p.? [37, 49].

2.8. Genotype–phenotype correlation

There are no clear genotype–phenotype correlations for ERCC6 or ERCC8 [1]. There are, however, group trends. In the Strasbourg series, the median severity score at diagnosis was 6 in the 22 CSA patients and 4 in the 43 CSB patients, a significant difference, with less severe disease in CSA patients [35]. In CoSyNH, CSB variants had a borderline significant association with shorter survival (P = 0.045), with no association with time to tremor, deafness or contractures [18]. In Laugel's 2013 review, among 101 patients with a known clinical subtype (28 CSA and 73 CSB), 56% of CSB patients met type II criteria and 75% of CSA patients were type I, a trend the author asks to be replicated in larger series [49]. In ERCC6, variants upstream of the PGBD3 insertion in intron 5 are associated with less severe disease than downstream variants [44, 50]. A Russian cohort of seven patients, published in 2026, found among four CSB patients one severe, two moderate and one mild case, and related severity mainly to onset before 1 year [51]. These observations are group-level and are not suitable for individual prognosis [9].

2.9. Allelic disorders and overlapping forms

ERCC6 is associated with CS type B, COFS1, UVSS1 and, in the heterozygous state, with premature ovarian insufficiency described in one study [1, 6, 7]; OMIM provisionally associates it with De Sanctis-Cacchione syndrome, based on two siblings homozygous for the truncating variant NM_000124.4:c.2203C>T p.(Arg735Ter), the same variant described in patients with Cockayne syndrome type B, and also lists susceptibility associations with age-related macular degeneration and lung cancer [38]. In the original series of 16 CSB patients with 18 inactivating variants, neither the site nor the type of variant correlated with severity [38]. ERCC8 is associated with CS type A and UVSS2, the latter described, for example, in a 15-year-old French girl homozygous for NM_000082.4:c.1083G>T p.(Trp361Cys), with photosensitivity and freckles, reduced recovery of RNA synthesis and a normal response to reactive oxygen species [39]; a biallelic result in ERCC8 does not by itself predict the prognosis of Cockayne syndrome, because other biallelic variants of the same gene cause UVSS [1, 9]. COFS can result from ERCC6 (COFS1, the original form), ERCC2 (COFS2, with severe cutaneous photosensitivity, an association that OMIM keeps as provisional), ERCC5 (COFS3) and ERCC1 (COFS4) [2, 26, 52–54]. In the XP/CS complex, among 42 patients with a known complementation group, 21 were XP-G (ERCC5), 13 XP-D (ERCC2), 5 XP-B (ERCC3) and 3 XP-F (ERCC4) [10]. Orphanet also associates ERCC4 with CS type 1 and ERCC1 with CS type 2 [12, 13]. A single patient with a homozygous truncating UVSSA variant and a progeroid phenotype resembling Cockayne syndrome, who died at 15 years, has been described as a possible phenotypic expansion, without replication [4, 55].

3. Clinical Spectrum and Manifestations by System

3.1. Data sources and the continuous spectrum

The clinical description rests on four types of data: Nance and Berry's review of 140 published cases (1992); Natale's survey (2011) of 45 patients supplemented by the literature; CoSyNH, with 102 patients from 81 families of four major ethnic groups, recruited in the United Kingdom and through an international network, with a mean age of 11.5 years (3 months to 39 years), 28 deaths and a mean age at death of 8.4 years (17 months to 30 years); and the French (Strasbourg), Japanese and Chinese series [17, 18, 24, 34, 35, 56]. In CoSyNH, genetic confirmation in 40 lineages showed CSB variants in 28 (70%), CSA variants in 11 (27.5%) and XPD variants in 1 (2.5%) [18]. The CoSyNH frequencies, collected systematically from primary sources, differ from those of the 1992 review, which was based on published reports [18]. All these series mainly describe patients without disease-modifying therapy, so they correspond to natural history under supportive care.

Table adapted from GeneReviews, which is based on Laugel (2013) and CoSyNH [1].

3.2. Pregnancy and the neonatal period

In CoSyNH, 87 of the 102 patients had prenatal ultrasound and anomalies were detected in 21: fetal growth restriction in 15, with a female-to-male ratio of 2:1, ventriculomegaly in 4 and microcephaly in 2 [18]. Of the 90 deliveries with information, 27% were caesarean sections, 4% instrumental deliveries and 69% vaginal deliveries; birth weight was almost always within the normal range (centiles 0.4 to 99.6) and most newborns were normocephalic, so the first occurrence in a family is very difficult to recognise before or during delivery [18]. In COFS, by contrast, the picture is usually evident at birth, and the disease can be recognised during prenatal surveillance and can cause spontaneous fetal death [1, 26].

3.3. Growth and nutrition

Postnatal growth failure and microcephaly are the cardinal features. In CoSyNH, birth parameters were at the lower limit of normal (median weight −0.76 ± 1.20 standard deviations, SD; head circumference −1.17 ± 1.29 SD) and, later, median head circumference reached −7.34 ± 2.96 SD, height −6.62 ± 3.09 SD and weight −6.62 ± 4.79 SD [18]. The authors consider the expression “progressive microcephaly” inappropriate: head circumference may be normal at first, but growth velocity falls rapidly until it stops, often between 1 and 2 years, and height and weight stop somewhat later [18]. The specific growth charts of 88 patients (49 type 1 and 39 type 2, with 1626 measurements) show that in type 1 microcephaly appears at about 2 months and restriction of weight and height between 5 and 22 months, whereas in type 2 the parameters are below reference values at birth or fall below the 5th centile before 3 months; height and head circumference are more affected in type 2 and weight is similar in both types [57]. Final height and weight rarely exceed 115 cm and 20 kg [5].

Postnatal feeding difficulties affected 48% of the CoSyNH cohort and gastro-oesophageal reflux disease 57% [18]. The progressive loss of subcutaneous fat, present in 56%, is inexorable and is not prevented by increased caloric intake; at this stage the stomach tolerates increases in meal volume poorly, which can cause vomiting [18]. Constipation, loose stools and difficult-to-control nappy dermatitis are common [18]. Loss of subcutaneous fat favours leakage around gastrostomy tubes [18].

3.4. Face, skin, hair and teeth

In the first months the face may look normal or merely “crowded”, with small eyes; the typical appearance, with loss of subcutaneous and orbital fat, a prominent nose and sunken eyes, develops over time, and some patients develop sunken eyes without generalised fat loss [18]. Children often hold their upper limbs in flexion [18]. Photosensitivity is variable: of 99 CoSyNH patients, 23 had no photosensitivity, 46 burned easily and 40 had overt photosensitivity, with burning on cloudy days or blistering after exposure [18]. The reference dysmorphology textbook reports photosensitive dermatitis in 75%, and the four-centre series estimates that about half of patients with diagnostic symptoms have photosensitivity and an abnormal cellular response to UV [5, 44]. There is no increased risk of skin cancer [1, 18]. Thin hair (46%) and hyperpigmentation (29%) have no clinical significance; anhidrosis and malar erythema are also described [1, 18, 56]. Laugel considers photosensitivity clinically evident in two-thirds to three-quarters of patients and uncorrelated with overall severity, which is not explained by differences in exposure or sun protection alone, and found no skin cancer in patients with ERCC6 or ERCC8 variants, only in the XP/CS complex [49]. Dental caries occurred in 46.4% of CoSyNH patients (50–75% in Laugel's review) and probably reflect enamel hypoplasia, which Laugel describes in almost all patients, alongside dental malposition, hypodontia and shovel-shaped upper central incisors; delayed eruption of the primary dentition, absent or hypoplastic teeth, shape anomalies and malocclusion are also described [1, 18].

3.5. Eyes and hearing

Cataracts and photophobia occurred in 48.5% of the CoSyNH cohort; cataracts are bilateral in most and 86% (38/44) appear by 4 years of age [18]. In type I, GeneReviews reports pigmentary retinopathy in 60–100% and cataracts of various types in 15–36%, as well as an abnormal electroretinogram, optic atrophy, miosis, reduced or absent tears, enophthalmos, strabismus, nystagmus and narrowed retinal arterioles [1]. “Salt-and-pepper” retinal dystrophy was present in 43% of CoSyNH patients [18]. In type II, congenital cataracts or other structural eye anomalies occur in 30% [1]. The electroretinogram shows abnormal photopic and scotopic responses well before visual impairment, optic disc pallor almost always accompanies retinal degeneration and may precede it, and miotic pupils respond poorly to mydriatics, which can make cataract surgery difficult [49].

Deafness is almost always bilateral; it presented in the neonatal period in 21% (14/68) and reached 84% by 10 years of age in CoSyNH [18]. Although described as sensorineural, 44% (20/45) of patients with detailed assessment had a conductive or mixed component [18]. Deafness has peripheral and central components [58].

3.6. Nervous system

Developmental delay is followed by progressive behavioural and intellectual deterioration in all patients, and early development may appear normal [1, 18]. Some children never roll over [18]. Common neurological findings in type I include spasticity, hyper- or hyporeflexia, stooped posture, abnormal gait or inability to walk, ataxia, tremor, incontinence, abnormal or absent speech, seizures, muscle wasting and behavioural changes [1]. In CoSyNH, tremor affected 66%, mainly intention tremor, sometimes with apparent regression of fine and gross motor performance, and seizures 23%, persistent in most and with no predominant type [18]. Weakness affected 79%, progressive in 49% (39/80) [18]. Peripheral neuropathy is demyelinating on nerve conduction studies and presents with weakness and hypo- or areflexia [1, 5]. In the Strasbourg series, the neurological signs combine pyramidal, extrapyramidal, cerebellar and peripheral components [35].

Computed tomography (CT) or magnetic resonance imaging (MRI) was abnormal in 83.5% (71/85) of CoSyNH patients: calcifications in 55% (47/85), mainly in the basal ganglia, sometimes diffusely cortical; white matter changes in 38% (33/85), due to dysmyelination or hypomyelination; cerebellar hypoplasia or atrophy, ventriculomegaly and a thin corpus callosum [18]. Dysmyelination is usually present from the outset, cerebral and cerebellar atrophy appears and worsens over the course of the disease, and calcifications may be absent in the early stages, becoming more evident with time [1]. The Japanese series recorded basal ganglia calcification on CT in more than 90% of type 1 patients, appearing later than photosensitivity and language delay [17].

3.7. Musculoskeletal system

Contractures mainly affect the lower limbs (64% in CoSyNH); 26% (11/42) are present in the neonatal period, but they can appear at any age [18]. In the Japanese series, contracture of the foot joints was among the seven findings present in more than 90% of type 1 patients, and in a Chinese series of eight CSA patients all developed Achilles tendon contracture [17, 56]. Scoliosis affected 48%, progressive in 49% (24/49) [18]. Radiology shows a thickened calvarium, a small sella turcica, biconvex flattening of the vertebrae, sclerotic “ivory” epiphyses, a small “squared” pelvis with hypoplastic iliac wings, and osteoporosis [5]. Progressive kyphosis, cold hands and feet, and flexion contractures complete the picture [5].

3.8. Kidney and blood pressure

In a French review of 136 genetically confirmed patients, 32 had renal investigation and 69% of these had kidney disease and/or raised blood pressure: hypertension in 15/21 (71%), proteinuria in 10/16 (62%), with nephrotic syndrome in 4, reduced glomerular filtration rate in 13/29 (45%) and hyperuricaemia in 18/25 (72%), with no correlation with gene or clinical type [59]. These denominators are small and reflect patients selected for investigation. In CoSyNH, where blood pressure was measured in 67 patients, 18% (12) were hypertensive; renal ultrasound, performed in 37, was abnormal in 4 (functioning hypoplastic kidney, abnormal shape and stones), and one patient had nephrotic syndrome at 6 years [18]. In the Japanese series, 9 of the 20 deceased type 1 patients had severe renal failure in the terminal phase [17].

3.9. Liver, endocrinology and other systems

Liver function tests were abnormal in 63% of the 71 CoSyNH patients tested, usually with mild transaminase elevation, which may increase progressively, and sometimes cholestasis [18]. In the Strasbourg series, with unpublished data summarised by Laugel, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were typically between 2 and 10 times the upper limit of normal, with an AST/ALT ratio below 1 and no change in coagulation factors; at least two deaths from acute liver failure have been described [49]. In the Chinese series, liver dysfunction paralleled severity and progression [56]. Of the 47 CoSyNH patients with blood glucose assessment, 13% (6) had abnormal glucose metabolism, in the older patients, with progression of glucose intolerance to insulin requirement; the earliest case of treated diabetes appeared at 16 years [18]. Eight patients had hypothyroidism, with an unknown denominator, and an older series described reduced or undetectable thyroid hormones in seven patients [18, 60]. Growth hormone (GH) stimulation tests gave conflicting results between studies, insulin-like growth factor 1 (IGF-1) is usually normal, and GH therapy produced no significant growth in at least one patient [49]. Cryptorchidism in one-third of boys, delayed or absent sexual maturation, poorly developed breasts and irregular cycles are also described [1, 5].

Cold extremities, present in 88.4%, are the most frequent non-cardinal feature, and venous access was difficult in 70% [18]. Echocardiography, performed in 38 patients, was abnormal in one (heart failure); other reports describe dilated cardiomyopathy and dilatation of the ascending aorta [18]. Twenty patients had respiratory problems, 15 with respiratory infections attributed to aspiration, and restrictive lung disease and asthma have also been described [18]. There is no immunodeficiency or increased incidence of infections [18]. Occasional manifestations include arrhythmias, peripheral vascular disease, strokes, subdural haemorrhage, hepatosplenomegaly and liver failure [5].

3.10. CS type II and COFS

In type II, growth failure is present at birth, there is little or no postnatal neurological development, early contractures of the spine and joints, and death usually by 5 years [1]. On the severity score, type II patients already have a slightly reduced score at birth and a rapid fall to a low plateau [35]. COFS adds neurogenic arthrogryposis, extreme congenital microcephaly, congenital cataracts, microphthalmia, microcornea, iris hypoplasia, optic atrophy and blepharophimosis [1, 26]. Neuropathological examination and imaging show reduced white matter, gliosis, focal microgyria, hypoplasia of the optic tracts, agenesis of the corpus callosum and calcifications of the lenticular nuclei and white matter [26]. The limbs show camptodactyly, flexion contractures of the elbows and knees, rocker-bottom feet with vertical talus and a longitudinal plantar crease; the face has a prominent nasal root, large ears and an upper lip overlapping the lower lip [26]. Children have axial hypotonia and peripheral hypertonia, hypo- or areflexia, occasional infantile spasms, severe neonatal feeding difficulties, virtually no growth and progressive cachexia despite apparently adequate caloric intake, with death usually from pulmonary infection before 5 years [26, 28]. In COFS due to ERCC2, severe cutaneous photosensitivity is added; OMIM records a single patient, the child of Ashkenazi Jewish parents, compound heterozygous for a null variant known in XP-D and a novel variant [26, 61]. In COFS3, due to ERCC5, there is marked cutaneous photosensitivity and survival beyond 6 years is rare; a boy born to Moroccan cousins died at 7 months, and in a Pakistani family five fetuses of three cousin couples had contractures and microcephaly detected in the second trimester [62]. In COFS4, due to ERCC1, the cells have a combined defect of TC-NER and GG-NER [63].

3.11. CS type III and adult-onset forms

In type III, the main features only become evident after 2 years and growth or cognition exceed what is expected for type I; sequencing has confirmed the diagnosis in patients with this profile [1]. Criteria for suspicion include short stature, mild neurological impairment and progressive ataxia in children or adolescents, particularly with photosensitivity [1]. The severity score remains normal in the first years and then declines slowly [35]. In Natale's mild group, the mean age at death was 30.3 years, and the “UV sensitivity only/adult onset” group described in the same study overlaps with UVSS [34]. Two siblings with biochemically confirmed Cockayne syndrome type B survived to 42 and 55 years, with mild intellectual disability, slowly progressive gait disturbance, tremor, cataracts, mild deafness and cerebral calcifications [64]. Reproductive capacity has only been documented in this form [1]. Laugel distinguishes from type III the adult-onset forms linked to ERCC6, asymptomatic until adulthood apart from short stature or photosensitivity in some cases, with normal intellectual development and presenting with progressive ataxia, early dementia and deafness between 30 and 40 years of age [49].

3.12. Ultraviolet-sensitive syndrome

UVSS, in its three types, presents in childhood with cutaneous photosensitivity with easy sunburn and mild dyspigmentation or freckling, sometimes telangiectasias, without skin tumours, without growth or developmental abnormalities and without neurological disease [4, 15, 36, 65]. The cellular defect is indistinguishable from that of Cockayne syndrome, and the disease is probably underdiagnosed [36]. The first patient, a Japanese boy described in 1981, had at 8 years freckles, hypopigmented macules, telangiectasias and dry skin in exposed areas, without growth delay or neurological disease; his fibroblasts were five times more sensitive to UV, and at 33 years he was 183 cm tall and healthy apart from photosensitivity; he was homozygous for ERCC6 p.(Arg77Ter) [38, 66]. UVSS2 was described in a French girl with sunburn from 4 months and facial freckles, with normal development [67]. Orphanet records about seven cases, and consanguineous families from Pakistan and Iran with UVSSA variants have been described [4, 15].

3.13. XP/CS complex

The XP/CS complex combines the extreme photosensitivity, freckling and skin cancer risk of xeroderma pigmentosum with the systemic and neurological features of Cockayne syndrome [3, 5]. In a review of 43 patients, the clinical picture was very similar to that of Cockayne syndrome without xeroderma pigmentosum, except for skin cancers; the incidence of cancer was lower than in classic or neurological xeroderma pigmentosum and higher than in Cockayne syndrome, and the most severely affected patients reached fewer milestones and died earlier [10]. Unlike Cockayne syndrome, XP/CS cells have reduced UDS and RRS [35]. A “pellagra-like” condition described about three decades ago, partially responsive to niacin, was reassigned by exome sequencing to XP/CS due to an ERCC5 variant [68].

4. Clinical Recognition and Red Flags

4.1. When to suspect

CoSyNH proposes suspecting Cockayne syndrome in any child with postnatal growth failure and microcephaly who also has two of the following features: persistently cold hands and feet, bilateral deafness, cutaneous photosensitivity, (intention) tremor, joint contractures, progressive loss of body fat, cataracts or typical facies [18]. With this rule, clinical recognition in the cohort rose to about 90%, whereas the previously published criteria, which required developmental delay, would have identified only 36% of patients, and only 20% if mild forms of photosensitivity were not recognised [18]. Developmental delay discriminates poorly in the first years, because early development may be normal [18].

The pattern by age guides suspicion. In the prenatal and neonatal period, the combination of arthrogryposis, microcephaly, congenital cataracts and microphthalmia suggests COFS, and growth restriction at birth with congenital cataracts suggests type II [1]. In the first 2 years, deceleration of head growth, weight and height, photosensitivity and language delay are the first signs; deafness, sunken eyes and basal ganglia calcifications appear later [17, 57]. In older children and adolescents, short stature with progressive ataxia and mild neurological deficit suggests type III [1].

Clinical genetics textbooks place Cockayne syndrome in the differential diagnosis of several presenting signs: cataracts in childhood with deafness, sun sensitivity or failure to thrive; intracranial calcifications with photosensitivity; hypomyelinating leukoencephalopathy with growth failure; developmental regression with deceleration of head circumference; pigmentary retinopathy with deafness; and microcephaly with short stature [69–74]. Early spasticity often leads to an initial diagnosis of cerebral palsy: the eight CSA patients of a Chinese series were classified in this way before genetic testing [56].

4.2. Clues against the diagnosis

Laugel adds that brain malformations, in particular anomalies of cortical gyration, have not been described in confirmed cases and should count as a sign against the diagnosis, as should cardiac or renal malformations [49]. GeneReviews lists as signs of an alternative diagnosis congenital anomalies of the face, limbs, heart or viscera; recurrent infections beyond otitis and respiratory infections; metabolic or neurological crises; haematological abnormalities such as anaemia or leucopenia; and cancer of any type [1]. The presence of freckles, lentigines or early skin cancer in a patient with Cockayne features points to the XP/CS complex [3, 10].

4.3. Red flags in diagnosed patients

Acute liver failure in the days following treatment with metronidazole is a potentially fatal emergency: in the CoSyNH cohort, eight patients (8%) had acute liver failure after metronidazole, three died, with intervals of 6 to 11 days between the first dose and death, and two also had an acute neurological deficit [19]. The picture resembles untreated paracetamol poisoning, with very high transaminases and coagulopathy [18]. Recurrent respiratory infections suggest aspiration and should prompt swallowing assessment [18]. Hypothermia or unexplained symptoms warrant thyroid function testing [18]. After sedatives or opioids, respiratory depression or flattened affect may occur for several days [18].

4.4. Newborn screening

There is no newborn screening for Cockayne syndrome in the sources consulted; in the Christian Arab community of Israel, the ERCC8 founder variant has been included in a carrier screening programme [47].

5. Diagnosis: Criteria, Testing, and Algorithms

5.1. Clinical criteria

The GeneReviews criteria, derived from Nance and Berry (1992) and revised by Natale (2011) and Laugel (2013), comprise two major and six minor criteria [1]. The major criteria are postnatal growth failure, with height and weight below the 5th centile at 2 years, and progressive microcephaly with neurological dysfunction, documented by early delay and later deterioration and by MRI showing dysmyelination and cerebral and cerebellar atrophy [1]. The minor criteria are cutaneous photosensitivity, demyelinating peripheral neuropathy, pigmentary retinopathy and/or cataracts, sensorineural deafness, dental anomalies, and a “cachectic dwarfism” appearance with sunken eyes [1].

Source: GeneReviews [1].

For COFS, Laugel and colleagues proposed stricter criteria in 2008, based on genetically confirmed cases: congenital microcephaly, congenital cataracts and/or microphthalmia, arthrogryposis, severe developmental delay, severe postnatal growth failure and facial dysmorphism with a prominent nasal root and/or an upper lip overlapping the lower lip, together with a defect of transcription-coupled repair [28, 75].

Laugel's 2013 review underlies the revision of the criteria. In a personal series of 120 consecutive cases referred to the Strasbourg laboratory on clinical suspicion, of which 29 had cellular and molecular confirmation, the Nance and Berry criteria had a specificity of 88%, sensitivity of 90%, negative predictive value of 96% and positive predictive value of 70% [49]. To reduce false positives, Laugel proposed making progressive microcephaly a third major criterion, requiring progressive growth failure, replacing caries with enamel hypoplasia and “cachectic dwarfism” with progressive bilateral enophthalmos; applied to the same series, the modified criteria would have had a specificity of 98%, sensitivity of 90% and positive and negative predictive values of 97% [49]. These values come from unpublished data from a single reference laboratory, in a preselected sample, and have not been independently validated.

Source: Laugel (2013), Table 1 [49].

The modified criteria apply to types I, II and III and leave out the extremes of the spectrum: COFS has its own criteria and, for adult-onset forms, Laugel proposes that the combination of short stature or photosensitivity with progressive cognitive decline, ataxia or deafness is enough to request DNA repair studies [49]. Because the disease is progressive and the criteria may only be met months or years after the first signs, requiring two minor criteria instead of three in the early stages increases the sensitivity of suspicion at the expense of specificity [49]. On imaging, hypomyelination and white matter atrophy, cerebellar atrophy or hypoplasia and bilateral putaminal calcifications had diagnostic value in the same series [49].

5.2. Spitz diagnostic scores

The system of Spitz and colleagues was built by logistic regression in 69 molecularly confirmed patients and 81 patients with a similar phenotype in whom Cockayne syndrome had been excluded, all referred to the Strasbourg laboratory [35]. Microcephaly, although constant, was not included in the score because it does not discriminate between neurodegenerative diseases, and pigmentary retinopathy, specific but difficult to detect in young children, was also left out [35].

Source: Spitz and colleagues, table 2 [35].

At the optimal threshold of 8.5, the clinical score had a sensitivity of 95.7% and specificity of 86.4%; the median was 12 in patients with Cockayne syndrome and 6 in controls [35]. The clinical-radiological score, which requires CT and MRI, had a sensitivity of 96.2% and specificity of 96.8% at a threshold of 15.5 (52 patients and 63 controls) [35]. In the same cohort, the Nance and Berry criteria had a sensitivity of 78.8%, specificity of 88.7%, positive predictive value of 85.9% and negative predictive value of 82.7% [35]. The authors stress that the score does not replace clinical expertise or molecular confirmation, that it was derived retrospectively in a single centre, that it needs prospective validation and that the appropriate threshold may depend on disease duration [35].

5.3. Molecular testing

The molecular diagnosis is established by identifying biallelic pathogenic or likely pathogenic variants in ERCC6 or ERCC8 [1]. CoSyNH adopted molecular testing of CSA and CSB as first line, on DNA from blood, mouthwash or dried blood spot, because it avoids the uncertainty of equivocal cellular assays, provides the recurrence risk and enables prenatal diagnosis and carrier testing; if CSA and CSB are normal in a COFS phenotype, it recommends studying ERCC5 [18]. GeneReviews proposes two options: a multigene panel including ERCC6, ERCC8 and the genes of the differential diagnosis, when the phenotype and imaging suggest the disease; or exome or genome sequencing, when the phenotype is atypical [1]. The panel should include the xeroderma pigmentosum and COFS genes to cover the overlapping forms [1, 2].

The limits of testing must be known. Deletions and duplications of one or more exons account for about 10% of ERCC6 variants and 12% of ERCC8 variants and are missed by sequencing alone [1]. Non-coding ERCC8 variants may require genome sequencing [1, 45]. A synonymous variant at the exon-intron boundary can alter splicing, as in the case described in section 10, in which the initial exome was negative and targeted reanalysis, with RNA studies, established the diagnosis [48]. When the exome is not diagnostic, an exome array can detect exonic deletions or duplications [1]. Two variants of uncertain significance, or one pathogenic variant and one of uncertain significance, neither establish nor exclude the diagnosis [1]. A biallelic result in ERCC6 or ERCC8 does not by itself distinguish Cockayne syndrome from UVSS, which has the same cellular defect, and the phenotype must be established clinically [9]. Apparent homozygosity requires consideration of an undetected deletion on the other allele or uniparental isodisomy [1]. The report should state the gene, the versioned transcript (NM_000124.4 for ERCC6, NM_000082.4 for ERCC8), the Human Genome Variation Society (HGVS) designation, the zygosity, the American College of Medical Genetics and Genomics and Association for Molecular Pathology (ACMG/AMP) classification and parental segregation testing [1, 37].

5.4. Functional assays in fibroblasts

Assays in cultured skin-biopsy fibroblasts show, in Cockayne syndrome, marked UV sensitivity and defective recovery of RNA synthesis after irradiation, with normal UDS [1, 35]. In classic xeroderma pigmentosum UDS is reduced, and in the XP/CS complex both UDS and RRS are reduced [35, 36]. The assays confirm the cellular phenotype but do not identify the gene, because ERCC6, ERCC8 and UVSSA give the same result, nor do they separate Cockayne syndrome from UVSS [4, 6, 9]. GeneReviews reserves them for strong suspicion with negative molecular testing [1]. CoSyNH adds that biopsy is usually unnecessary because, whenever there was a clear TC-NER defect, a molecular diagnosis could be reached, and that sequencing can resolve equivocal cellular results [18].

5.5. Imaging and other investigations

MRI shows dysmyelination or hypomyelination of the white matter and cerebellar atrophy, and CT detects basal ganglia and cortical calcifications with greater sensitivity [1, 70]. The clinical-radiological score scores leukoencephalopathy and calcifications [35]. CoSyNH considers that the intracranial findings are not pathognomonic, have no prognostic value and do not change management, and does not recommend routine imaging without a clinical indication; GeneReviews includes MRI in the initial evaluation [1, 18]. The electroretinogram is abnormal in classic disease [1].

5.6. Practical algorithm

5.7. Prenatal and preimplantation diagnosis

Once the familial variants have been identified, prenatal diagnosis and preimplantation genetic testing are possible [1]. The 2010 mutation update described cases of molecular prenatal diagnosis and discussed the strategy [33]. Prenatal ultrasound mainly identifies the COFS forms; in the classic forms, fetal parameters are usually normal [1, 18].

6. Differential Diagnosis

6.1. Comparison table

AR: autosomal recessive; AD: autosomal dominant; XL: X-linked; CSF: cerebrospinal fluid; SCE: sister chromatid exchanges; CMV: cytomegalovirus.

6.2. Excision repair disorders

The most important distinction is from xeroderma pigmentosum. In Cockayne syndrome there are no lentigines or skin cancer, neurodegeneration is demyelinating, with tendon reflexes often increased and calcifications, and cells have normal UDS; in neurological xeroderma pigmentosum there is pigmentation and early skin cancer, neuronal degeneration with hyporeflexia and reduced UDS [1, 36, 43]. The XP/CS complex combines both profiles, including the cutaneous and oncological aspects of xeroderma pigmentosum [10]. UVSS shares genes and cellular phenotype with Cockayne syndrome but has no systemic disease; the distinction is clinical, and a young patient with biallelic variants and photosensitivity only requires follow-up before a late-onset form is ruled out [9, 34, 36]. Trichothiodystrophy shares photosensitivity, growth failure and neurology, but is distinguished by the hair [36].

6.3. Leukodystrophies and intracranial calcifications

Cockayne syndrome enters the differential diagnosis of leukoencephalopathies with calcifications, alongside Aicardi-Goutières syndrome, band-like calcification with polymicrogyria due to OCLN, Coats plus disease due to CTC1, COL4A1-related disorders and leukoencephalopathy with calcifications and cysts [70]. Most leukodystrophies are not accompanied by growth restriction, with the exception of the severe connatal form of Pelizaeus-Merzbacher disease [1]. Skin clues are useful: photosensitivity in Cockayne syndrome, chilblains in Aicardi-Goutières syndrome, signs of adrenal insufficiency in X-linked adrenoleukodystrophy [71]. In the tables for the approach to inborn errors of metabolism, Cockayne syndrome appears among the hypomyelinating disorders, the leukodystrophies with calcifications and the genetic causes of cataracts with deafness [76].

6.4. Growth restriction and progeroid syndromes

In the infant with faltering growth, the combination of short stature, microcephaly and developmental delay brings DNA repair disorders, including Cockayne syndrome, into the differential diagnosis [77]. In profound growth restriction (Seckel, Cornelia de Lange, Rubinstein-Taybi, Wiedemann-Rautenstrauch, Silver-Russell, Dubowitz and Hallermann-Streiff), the distinctive physical appearance of Cockayne syndrome is the main discriminating element [1]. In progeroid and genomic instability syndromes (Rothmund-Thomson, Bloom, Hutchinson-Gilford progeria, Werner), photosensitivity or thinning of skin and hair can be confusing, but white matter changes, calcifications and neurodegeneration are absent [1]. Primary mitochondrial diseases share early pigmentary retinopathy, calcifications and neurodegeneration, and Cockayne syndrome may have lactic acidaemia and muscle mitochondrial DNA depletion [1, 42].

6.5. Conditions mimicking COFS and type II

At birth, RAB18 deficiency (Warburg micro syndrome and Martsolf syndrome) may resemble COFS or type II, because of microcephaly, microcornea and cataracts, but it lacks rapidly progressive neurodegeneration and NER is normal [1]. Arthrogryposis with microcephaly and ocular anomalies includes other genetic causes, and COFS should only be accepted with molecular confirmation, because many cases described outside the Manitoba population have not been confirmed [28, 78]. In the fetus with akinesia (severe reduction or absence of spontaneous movements), COFS is among the genetic causes to consider [79]. MORC2-related disease can closely reproduce the clinical picture, but has normal NER and no photosensitivity [1].

7. Treatment and Risk Management Strategies

7.1. Evidence base and recommendation documents

There is no disease-modifying therapy and no treatment of proven efficacy [1]. There are no guidelines from scientific societies; the reference documents are the CoSyNH care recommendations (2016), derived from the cohort of 102 patients and presented by the authors as the first simple guidance for the disease, and the GeneReviews chapter (2024 update), whose recommendations rest on the author's experience and on CoSyNH [1, 18]. No recommendation comes from a randomised trial. The aim of care is to maximise quality of life and avoid preventable harm [9, 18].

7.2. Organisation of care

Each patient should have a named, accessible coordinating clinician, usually a paediatrician, and a geneticist in adults [18]. CoSyNH also recommends a dietitian involved before supplementary feeding is needed and a physiotherapist or occupational therapist [18]. Many patients remain well and only need unplanned admission in the late stages, so they should be known to local services before then [18]. The team includes a speech and language therapist, because swallowing and communication show initial delay and later decline [80].

7.3. Management by manifestation

7.4. Nutrition and growth

The specific growth charts make it possible to distinguish the expected course from undernutrition and to avoid abrupt overhydration and overfeeding [57]. In CoSyNH, 63% (15/24) of patients who started nasogastric feeding moved to gastrostomy, with a mean interval of 7 months [18]. Because subcutaneous fat loss does not respond to increased calories and the stomach tolerates increasing volumes poorly, the authors advise modest increases with weight monitoring [18]. A metabolic study using indirect calorimetry to measure resting energy expenditure was terminated in Strasbourg because of insufficient recruitment [83].

7.5. Symptomatic medication

The drugs used (carbidopa-levodopa, baclofen, amlodipine, ACE inhibitors, proton pump inhibitors) are in common use and are prescribed at the usual paediatric doses, with no Cockayne syndrome-specific dosing in the sources [1, 18]. Carbidopa-levodopa reduced tremor and improved handwriting and handling of utensils in three patients, in a 2008 case report that proposed a clinical trial that was never conducted; in CoSyNH, few patients with tremor received treatment [18, 81]. In hypertension, one patient was controlled with a beta-blocker alone, at least one was refractory to this class and the rest were controlled with amlodipine, alone or combined with an ACE inhibitor or angiotensin II receptor antagonist [18]. For all these drugs, the heightened vigilance for sedation and the liver monitoring described below apply.

7.6. Agents and circumstances to avoid

Metronidazole. This is the only drug with a specific contraindication. In the CoSyNH cohort, eight patients (8%) had acute liver failure after metronidazole, three fatal, with 6 to 11 days between the first administration and death, and two had an acute neurological deficit; the authors identified no exposed patient without a serious adverse effect and recommend regarding the diagnosis of Cockayne syndrome as an absolute contraindication [19]. CoSyNH adds that antibiotics of the same class should be avoided or used with extreme caution and liver monitoring, and states that there is no evidence of toxicity of hepatically metabolised drugs in general [18]. GeneReviews recommends avoiding metronidazole under any circumstances [1]. Metronidazole is frequently prescribed for dental infections, aspiration pneumonia, abdominal sepsis and Clostridioides difficile infection, situations that are common in these patients, so the alert must reach paediatricians, general practitioners and dentists [9]. A 2026 letter again described metronidazole hepatotoxicity in children with Cockayne syndrome [84].

The divergence between labels does not change management: the reference is the clinical recommendation, and the labels serve for comparison. If, in an exceptional situation with no alternative, metronidazole is administered, the liver monitoring scheme in the labels is the only one described [85, 86].

Opioids and sedatives. Five CoSyNH patients had an exaggerated response, ranging from respiratory depression to flattened affect lasting several days after codeine; CoSyNH recommends considering starting opioids at one-third of the usual dose and monitoring sedatives [18]. GeneReviews recommends heightened vigilance with both [1].

Growth hormone. Growth hormone levels may be raised or reduced; because the absence of cancer risk may depend on the concurrent deficit in transcription and proliferation, growth hormone could theoretically promote tumour growth and, in the absence of safety and efficacy data, cannot be recommended [1].

Sun exposure. Excessive sun exposure should be avoided [1].

7.7. Regulatory status

7.8. Registered trials and studies

The only registered interventional study, that of Prodarsan®, has no public results and the sponsor has ceased operating; the others are observational [83]. There are therefore no comparative trials with confidence intervals to report, and none of the studies of symptomatic treatment (carbidopa-levodopa, cochlear implant, contracture rehabilitation) goes beyond the level of a case series [56, 58, 81]. A search of ClinicalTrials.gov found no active trials of targeted therapy; this absence does not exclude unregistered studies [83]. The Spitz severity score has been proposed as an outcome for future trials, similar to the scales used in neuronal ceroid lipofuscinosis and in gene therapies for spinal muscular atrophy [35].

7.9. Developments in the past 12 months

No marketing applications, opinions or authorisations for Cockayne syndrome were found in the sources consulted [83]. Niacin, which protected XP/CS fibroblasts from UV-induced damage and improved skin lesions in one family, remains an untested hypothesis [68].

7.10. Anaesthesia and surgery

The main anaesthetic concerns are the difficult airway and the risk of gastric aspiration: in three patients, tracheal intubation was difficult in two and the laryngeal mask airway was useful [88]. Subglottic stenosis, myocardial ischaemia and delayed recovery after anaesthesia have been described, as well as an unusual blood pressure response to local anaesthetic in dental surgery [89–91]. During induction with 8% sevoflurane, the bispectral index fell to single digits with a suppression ratio above 40% and stable haemodynamics, which led the authors to recommend titrating anaesthetics by electroencephalography [92]. Venous access is difficult in 70% and should be performed by experienced staff [18]. In a 10-year-old boy with very high transaminases, orthopaedic surgery proceeded without complications after multidisciplinary review, avoidance of hepatotoxic agents, choice of volatile anaesthetics and conservative titration of opioids and sedatives [82]. Metronidazole must be excluded from surgical antibiotic prophylaxis [19].

7.11. Pregnancy and lactation

There is no record of reproduction in types I and II [1]. A successful but very difficult pregnancy has been described in a young woman with a mild form; the small pelvis and abdomen limit fetal growth, and prevention of preterm delivery and caesarean section under spinal anaesthesia are usually required [1, 93, 94]. In Brazil, a pregnant woman with Cockayne syndrome underwent caesarean section for cephalopelvic disproportion under spinal anaesthesia, in a decision that weighed the difficult airway against cardiovascular, respiratory and neurocognitive limitations [89]. The sources consulted do not describe lactation data.

7.12. Transition to adult services

Transition is difficult, because adults with Cockayne syndrome are small and many adult services are not equipped for patients of this stature; where this is the case, CoSyNH recommends negotiating continuity in paediatric services locally, and the geneticist can coordinate adult care [18].

7.13. Divergences between recommendations

8. Reproductive Options and Family Counselling

8.1. Recurrence risks

All forms of the spectrum are autosomal recessive [1]. The parents of a patient are presumed to be heterozygous, and parental testing is recommended to confirm the phase of the variants and to calculate the recurrence risk reliably [1]. If both are carriers, each sibling has, at conception, a 25% chance of being affected, 50% of being an asymptomatic carrier and 25% of being neither affected nor a carrier; affected siblings usually become recognisable in the first years of life [1]. Carriers are asymptomatic and do not develop the disease [1]. Heterozygosity for variants affecting the CSB-PGBD3 fusion has been associated, in one study, with premature ovarian insufficiency, a distinct dominant phenotype that Cockayne syndrome counselling sources do not incorporate into carrier risk [1, 6, 7].

8.2. Cascade and carrier testing

Carrier testing of relatives requires prior identification of the familial variants [1]. Testing the reproductive partner of a known carrier should be considered, particularly when they share the same ancestry, because there are founder variants in Druze, Amish, Christian Arab and Finnish communities [1, 46, 47]. In the Christian Arab community of northern Israel, the carrier frequency of the ERCC8 p.(Tyr322Ter) variant was 6.79% (95% CI 3.84–9.74%), and the variant was included in the genetic screening programme offered to this community [47]. CoSyNH reports carrier frequencies of up to 1 in 15 in genetically isolated communities in Israel; in a Druze village with an extended family affected by severe disease, the familial ERCC6 variant was found in 7 of 106 healthy Druze (about 1 in 15); the six patients in that family had the severe congenital form and died before 5 years [18, 64].

8.3. Prenatal and preimplantation diagnosis

The ideal time to assess risk and discuss prenatal or preimplantation diagnosis is before pregnancy, and counselling should be offered to young adults who are affected, carriers or at risk of being carriers [1]. With the familial variants known, molecular prenatal diagnosis is possible and has been described [1, 33]. Without known variants, ultrasound is of little help in the classic forms, because fetal growth and head circumference are usually normal; anomalies such as growth restriction, ventriculomegaly or microcephaly were detected in 21 of 87 pregnancies studied in CoSyNH [18]. In COFS, ultrasound may detect microcephaly, cataracts and arthrogryposis, and the disease causes fetal deaths [1]. Views on the use of these tests vary among professionals and families [1].

8.4. Counselling of minors and the family

Carrier testing in asymptomatic minor siblings has no immediate clinical benefit, because carriers do not become ill, and the sources consulted do not propose a specific protocol; diagnostic testing of siblings with suggestive signs is distinct and is useful [1]. GeneReviews recommends assessing the family and social structure, drawing on social support, home nursing and patient associations [1]. CoSyNH advises against classification into types in conversations with families, because it is confusing, and prefers descriptive information about what they can expect [18].

9. Special Considerations: Population Diversity and Epidemiology

9.1. Europe

The study by Kleijer and colleagues pooled data from the DNA repair diagnostic centres of France, (West) Germany, Italy, the Netherlands and the United Kingdom, which have performed laboratory diagnosis of Cockayne syndrome since the mid-1980s, and estimated the incidence at 2.7 per million live births, including the XP/CS complex [16]. Because immigrant populations were over-represented among patients, the authors also calculated the incidence in the native population, 1.8 per million, slightly higher than that of xeroderma pigmentosum (0.9 per million) [16]. Orphanet records, from that study, birth prevalences per 100,000 of 0.45 in the Netherlands, 0.38 in the United Kingdom, 0.2 in Italy, 0.18 in France and 0.09 in Germany, a birth prevalence of 0.2 per 100,000 in Europe according to EUROCAT (2005–2012) and an annual incidence of 0.5 per 100,000; worldwide point prevalence is unknown [11]. The fivefold variation between countries reflects diagnostic capacity as much as biology [9]. These estimates are minimum figures, because the disease is probably underdiagnosed, partly because of reliance on photosensitivity for diagnosis [1, 18].

9.2. Japan, Russia and other regions

The Japanese national survey estimated an incidence of 2.77 per million births (95% CI 2.19–3.11) and a prevalence of about 1 in 2,500,000, with 47 patients: 41 type 1, 2 type 2, 3 type 3 and 1 CS/XP-D [17]. The first Russian cohort, of seven patients followed between 2023 and 2025, cites a frequency of 1 in 2.5 million [51]. The sources consulted provide no estimates for the USA. The predominance of type 1 patients in the Japanese series differs from the French series, in which one-third were type II, which may reflect differences in referral [17, 35].

9.3. Founder populations

The original COFS was described in an Aboriginal population of Manitoba, homozygous for an ERCC6 variant [25, 27]. In northern Finland, six COFS patients from four sibships of a consanguineous family shared a homozygous ERCC6 variant, inherited from a common ancestor who lived in a village in the north-east of the country in the 18th century; two of them, published in 1982, were the first COFS cases with cerebral calcifications [46]. The ERCC6 variant c.1034_1035insT is a founder variant in the Druze population of northern Israel, where it is associated with the severe congenital form [64], and c.2709+1G>T in the Amish population [1]. The ERCC8 variant p.(Tyr322Ter) is an ancient founder mutation in Christian Arabs of northern Israel, probably originating in the Lebanese Christian community [47].

9.4. Portugal and Brazil

The sources consulted include no epidemiological data from Portugal or Brazil, and no Portuguese centre appears in the ERN-Skin list of centres specialised in DNA repair disorders [21]. Laugel's 2013 review describes the ERCC8 variant c.618-1G>A as a founder variant in Portuguese and Brazilian patients and c.313_314del in Brazilian families, without stating the number of patients or the frequency in each country [49]. In Brazil, Bertola and colleagues studied, in 2006, eight patients from six families with typical Cockayne syndrome type A, all with biallelic ERCC8 variants and with no evident genotype–phenotype correlation, according to the OMIM description [60]. A report of caesarean section under spinal anaesthesia in a pregnant woman with Cockayne syndrome has also been published from Brazil [89].

9.5. European networks, centres and associations

Cockayne syndrome falls within the scope of ERN ITHACA (rare congenital malformations and intellectual disability), whose publications include the specific growth charts, and of ERN-Skin, whose GeneSkin platform lists centres specialised in DNA repair disorders, such as Rostock (ERN-Skin centre), Berlin (Charité), Rotterdam (Erasmus MC), Paris (Necker-Imagine), Bordeaux, Milan, Bologna, Florence, Rome, Innsbruck, Brno, Groningen, Lausanne, Dublin, Budapest and the national xeroderma pigmentosum service in London [20, 21, 57]. The French reference laboratory in Strasbourg holds the largest published clinical and cellular database [35]. Patient associations include Amy and Friends (United Kingdom and the Netherlands), Cockayne Syndrome Network (USA), Les P'tits Bouts (France) and the XP Society; the GenIDA registry has a module specific to Cockayne syndrome and the Myelin Disorders Bioregistry Project collects data from patients with leukodystrophies [1].

10. Illustrative Clinical Case

Bie and colleagues published in 2025 the case of a Chinese girl, the first child of healthy parents, born at term by caesarean section weighing 3.25 kg [48]. She had motor delay from the first year (head control at 4 months, sat at 8, stood at 15 and walked independently at 1 year and 8 months), abnormal gait, learning difficulties, slow speech, progressive dwarfism and microcephaly, and began rehabilitation at 3 years [48]. At 7 years she was admitted to the emergency department with 4 days of fever and thrombocytopenia, prostration, pneumonia, bilateral pleural effusion and right pneumothorax; she measured 98 cm (−5 SD), weighed 13 kg (< −3 SD) and had a head circumference of 47.5 cm (< −2 SD), wasting, sunken eyes, a beaked nose, limb hypertonia, brisk knee reflexes, bilateral Babinski sign, cutaneous photosensitivity and an aged appearance [48]. Tests showed platelets of 33 × 10⁹/L, proteinuria of 8.611 g/24 h, alanine aminotransferase of 117.2 U/L, urea of 21.05 mmol/L, creatinine of 124.9 µmol/L and uric acid of 466.3 µmol/L, with hepatosplenomegaly and ascites on ultrasound [48]. MRI was normal at 1 year and 7 months, showed reduced white matter and hypomyelination at 3 years and 8 months and, at 7 years, widened sulci in the cerebral and cerebellar hemispheres, hypomyelination and periventricular FLAIR hyperintensity (Figure 1) [48].

The exome performed at 3 years was considered negative [48]. Reanalysis at 7 years, targeted at ERCC6 and ERCC8, identified the maternal synonymous variant ERCC8 NM_000082.4:c.1041G>A p.(Gln347=), at the last base of exon 10, absent from population databases, and a paternal deletion including exon 1, confirmed by quantitative PCR and extending from intron 1 of ERCC8 to ZSWIM6 [37, 48]. RNA studies showed a product 198 base pairs shorter, corresponding to exon 10 skipping, which led to reclassification of the synonymous variant from uncertain significance to pathogenic (PVS1, PM2_supporting, PM3, PP4) [48].

The case brings together several features described in the cohorts: early development only mildly delayed, deceleration of head growth, weight and height, hepatic and renal involvement with nephrotic-range proteinuria and hyperuricaemia, and imaging progression from a normal initial MRI to hypomyelination and atrophy [1, 18, 59]. It also shows the limits of molecular diagnosis: a negative exome does not exclude the disease when the phenotype is suggestive, and targeted reanalysis with RNA studies can resolve splicing variants and deletions including the first exon [1, 48]. The report does not describe therapeutic management beyond admission nor the subsequent course; in a child with pneumonia and liver dysfunction, antibiotic choice must exclude metronidazole [19].

11. Prognosis and Long-Term Follow-Up

11.1. Survival

The mean age at death was 5.0 years in the severe group, 16.1 years in the moderate group and 30.3 years in the mild group, according to Natale's study, which combined 45 surveyed patients with literature data [34]. GeneReviews reports for type I death usually in the first or second decade, with a mean of 16 years and survival described into the third decade; for type II and COFS, death usually in the first decade, with prolonged survival in some cases; and for type III, survival into adulthood [1]. COFS usually has survival of less than 5 years [26]. In CoSyNH, with a mean age of 11.5 years at inclusion, 28 of the 102 patients had died, with a mean age at death of 8.4 years [18]. The most frequent causes of death are pneumonia, followed by renal failure, seizures, cardiac arrest, liver failure and stroke [5]. In the Japanese series, 9 of the 20 deceased type 1 patients had severe renal failure in the terminal phase, and stagnation of weight and height, language delay, tube feeding and renal failure were more frequent in deceased patients than in survivors [17].

11.2. Prognostic factors

Cataracts before 3 years are the strongest prognostic factor: in CoSyNH, 5-year survival was about 60% in patients with early cataracts and 95% in the others (P = 1.36 × 10⁻⁶), and early cataracts were also associated with earlier deafness (P = 4.43 × 10⁻⁷) and contractures (P = 0.028), but not with tremor or fat loss [18]. One dysmorphology textbook states that cataracts do not distinguish the severity groups, a position that CoSyNH contradicts with survival data [5, 18]. The degree of photosensitivity was not associated with survival (P = 0.23), but severe photosensitivity was associated with earlier contractures (P = 8.31 × 10⁻⁵) [18]. CSB variants were associated, at the threshold of significance, with shorter survival (P = 0.045) [18]. Age at symptom onset correlated positively with the severity score (ρ = 0.41; p < 0.01), and onset before 1 year was associated with faster progression in the Russian cohort [35, 51]. The most profound intellectual disability occurs in the earliest-onset cases, with a smaller head and more severe growth failure [5].

11.3. Severity score

Source: Spitz and colleagues, table 1; total score from 0 (most severe) to 15 [35].

In 65 patients, the median at diagnosis was 6 in type I, 3 in type II and 7 in type III; longitudinal follow-up of 19 patients showed that in type I the score is normal at birth and falls steadily from the first year, in type II it falls rapidly to a low plateau and in type III it maintains a normal plateau in the first years before a slow decline [35]. The score may help to tailor follow-up and has been proposed as a trial outcome, but it needs prospective validation [35].

11.4. Initial evaluation after diagnosis

The initial evaluation includes growth on specific charts and nutritional status; developmental assessment; brain MRI and neurological examination including tone; ophthalmological assessment, possibly with electroretinography; an audiogram; dermatological and dental assessments; radiographs if there are signs of skeletal dysplasia; renal and liver function; blood pressure; genetic counselling; and assessment of family and social needs [1]. CoSyNH adds early referral to a dietitian and physiotherapy and recording the metronidazole alert [18].

11.5. Surveillance table

11.6. Follow-up in UVSS and XP/CS

In UVSS, follow-up is limited to strict lifelong photoprotection and dermatological observation of dyspigmentation; the intensive cancer surveillance of xeroderma pigmentosum and the neurological surveillance of Cockayne syndrome are not indicated on the same basis [4]. In the XP/CS complex, the cutaneous and ophthalmological surveillance of xeroderma pigmentosum is added to the surveillance for Cockayne syndrome [10].

12. Summary and Concluding Remarks

Cockayne syndrome is an autosomal recessive disorder of transcription-coupled nucleotide excision repair, caused in about two-thirds of cases by ERCC6 variants and in one-third by ERCC8 variants, with a minimum European incidence of 2.7 per million live births. It forms a continuous spectrum ranging from COFS, of fetal onset, through types II, I and III, to UVSS, which shares genes and cellular defect but is confined to the skin; the XP/CS complex adds the skin cancer risk of xeroderma pigmentosum. The classic presentation is that of a child with normal growth and head circumference at birth who, between the first and second year, stops growing and develops microcephaly, sunken eyes, fat loss, deafness, cataracts, retinopathy, tremor, spasticity, contractures and variable photosensitivity, with leukodystrophy and calcifications on imaging and renal, hepatic and blood pressure involvement over the course of the disease.

Clinical recognition improves with the CoSyNH rule (postnatal growth failure and microcephaly with two accessory features) and with the Spitz score. The diagnosis is confirmed by sequencing of ERCC6 and ERCC8 with deletion/duplication analysis, extended to exome or genome and RNA studies when the panel is negative, and DNA repair assays in fibroblasts are reserved for cases without molecular resolution. A biallelic result does not by itself distinguish Cockayne syndrome from UVSS.

There is no targeted therapy. Care rests on a coordinating clinician, nutrition guided by specific growth charts and clinical status, physiotherapy, sensory and dental treatment, control of hypertension, reflux and tremor, and annual surveillance of renal and liver function, blood pressure, blood glucose from 10 years, hearing and vision. Metronidazole is contraindicated by the clinical recommendation, although several labels, including the Portuguese SmPC, treat it only as a warning; opioids and sedatives should be started at reduced doses, and growth hormone is not recommended. Cataracts before 3 years are the main marker of poor prognosis. Preclinical research in 2025–2026, with AAV9-CSA gene therapy in mice and studies of RNA polymerase II processing, NAD+ metabolism and mitochondrial function, has not yet reached trials in patients.

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