From OMIM
Cockayne syndrome (CS) is characterized by abnormal and slow growth and development that becomes evident within the first few years after birth. 'Cachectic dwarfism' describes the outward appearance of afflicted individuals. Other features include cutaneous photosensitivity, thin, dry hair, a progeroid appearance, progressive pigmentary retinopathy, sensorineural hearing loss, dental caries, and a characteristic stance in the ambulatory patient. Patients often show disproportionately long limbs with large hands and feet, and flexion contractures of joints are usual skeletal features. Knee contractures result in a 'horse-riding stance.' There is delayed neural development and severe progressive neurologic degeneration resulting in mental retardation. The mean age at death in reported cases is 12.5 years, although a few affected individuals have lived into their late teens or twenties. Remarkably, in striking contrast with xeroderma pigmentosum, patients with CS have no significant increase in skin cancer or infection (Nance and Berry, 1992). Lowry (1982) noted that there is an early-onset form of Cockayne syndrome in which patients may show abnormalities at birth and have a shorter survival. Lowry (1982) thus suggested that CS could be divided clinically into the more common type I, with classic CS symptoms that manifest within the first few years or life, and the less common type II, with more severe symptoms that manifest prenatally. Mallery et al. (1998) found no correlation between genotype and phenotype among 16 patients with CS of varying severities, and concluded that clinical differences were based on other genetic backgrounds or the intrauterine environment. Genetic Heterogeneity of Cockayne Syndrome Cockayne syndrome is a genetically heterogeneous disorder, and certain types show some overlap with certain forms of xeroderma pigmentosum (XP), another disorder caused by defective DNA repair. See also Cockayne syndrome B (133540), caused by mutation in the ERCC6 gene (609413) on chromosome 10q11; XPG/CS (see 278780), caused by mutation in the ERCC5 gene (133530) on chromosome 13q33; XPB/CS (see 610651), caused by mutation in the ERCC3 gene (133510) on chromosome 2q21; and XPF/CS (see 278760), caused by mutation in the ERCC4 gene (133520) on chromosome 16p13. Rapin et al. (2000) reviewed the clinical, pathologic, and molecular features of Cockayne syndrome, xeroderma pigmentosum, and the XP-CS complex.  http://www.omim.org/entry/216400