ERCC6

Cockayne Syndrome, Type B

Clinical Characteristics
Ocular Features: 

The eyes are deep-set.  Congenital cataracts are present in 30% of infants.  The aggressive course of this form of CS has precluded full delineation of the ocular features but infants have been described with microphthalmos, microcornea and iris hypoplasia. 

Systemic Features: 

Evidence of somatic and neurologic delays is present at birth or shortly thereafter with microcephaly and short stature.  Infants never develop normal milestones and may not grow in size beyond that of a 6 month-old child.  Communication skills are minimal.  They have a progeroid appearance, age rapidly, and most do not live beyond 5 years of age.   Feeding problems are common with considerable risk of aspiration, a common cause of respiratory infections and early death.  Severe flexion contractures develop early and may interfere with motor function.  Tremors and weakness contribute as well.  The skin is sensitive to UV radiation in some but not all patients.  However, the frequency of skin cancer is not increased.  Endogenous temperature regulation may be a problem. 

At least some cases with what has been called cerebro-oculo-facio-skeletal syndrome have been genotypically documented to have type B CS, the severe form of Cockayne syndrome.

Genetics

This is an autosomal recessive disorder resulting from mutations in ERCC6 (10q11) rendering the excision-repair cross-complementing protein ineffective in correcting defects during DNA replication.  Mutations in this gene account for about 75% of CS patients.  However, using date of onset and clinical severity, type A CS (216400) disease is far more common even though the ERCC8 mutations are found in only 25% of individuals.  Type A CS (216400) also has a somewhat later onset and is less severe in early stages.

Type III (216411) is poorly defined but seems to have a considerably later onset and milder disease.  The mutation is type III is unknown.

Some patients have combined  phenotypical features of cerebrooculofacioskeletal syndrome (214150) and xeroderma pigmentosum (XP) known as the XP-CS complex (216400).  Defective DNA repair resulting from mutations in excision-repair cross-complementing or ERCC genes is common to both disorders.  Two complementation groups have been identified in CS and seven in XP.  XP patients with CS features fall into only three (B, D, G) of the XP groups.  XP-CS patients have extreme skin photosensitivity and a huge increase in skin cancers of all types.  They also have an increase in nervous system neoplasms. 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Feeding tubes may be necessary to maintain nutrition.  Protection from the sun is important.  Physical therapy can be used to minimize contractures.  Cataract surgery might be considered in selected cases as well as assistive devices for hearing problems but the limited lifespan should be considered. 

References
Article Title: 

The Cockayne Syndrome Natural History (CoSyNH) study: clinical findings in 102 individuals and recommendations for care

Wilson BT, Stark Z, Sutton RE, Danda S, Ekbote AV, Elsayed SM, Gibson L, Goodship JA, Jackson AP, Keng WT, King MD, McCann E, Motojima T, Murray JE, Omata T, Pilz D, Pope K, Sugita K, White SM, Wilson IJ. The Cockayne Syndrome Natural History (CoSyNH) study: clinical findings in 102 individuals and recommendations for care. Genet Med. 2015 Jul 23. doi: 10.1038/gim.2015.110. [Epub ahead of print].

PubMed ID: 
26204423

Cockayne syndrome and xeroderma pigmentosum

Rapin I, Lindenbaum Y, Dickson DW, Kraemer KH, Robbins JH. Cockayne syndrome and xeroderma pigmentosum. Neurology. 2000 Nov 28;55(10):1442-9. Review. PubMed PMID:

PubMed ID: 
11185579

Cerebrooculofacioskeletal Syndrome

Clinical Characteristics
Ocular Features: 

Congenital cataracts and microphthalmia are frequent findings in this disorder.  Delayed mental development and early death in childhood have limited full delineation of the ocular phenotype.  Photosensitivity, nystagmus, optic nerve atrophy, and pigmentary retinopathy have been reported.  The eyes may appear deeply-set.

Systemic Features: 

Microcephaly, flexion contractures, prominent nasal root and an overhanging upper lip are common features.  Severe developmental and growth delays are evident early followed by progressive behavioral and intellectual deterioration.  Both hypotonia and hyperreflexia have been described.    Kyphosis and scoliosis are common.  CT scans may show intracranial calcifications and brain histology shows severe neurodegeneration with neuronal loss and gliosis.  Respiratory distress may also occur and some individuals have died in the first decade of life.

Genetics

Homozygous mutations in the ERCC6 gene (10q11) seem to be responsible for this autosomal recessive disorder.  Several sets of parents have been consanguineous.  Mutations in the same gene are responsible for Cockayne type B syndrome (133540) and some suggest that the variable phenotype represents a spectrum of disease rather than individual entities. Cerebrooculofacioskeletal syndrome represents the more severe phenotype in this spectrum.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for this disorder.

References
Article Title: 
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