Xeroderma pigmentosum-Cockayne syndrome complex

Xeroderma pigmentosum-Cockayne syndrome complex (XP-CS complex, also known as XP/CS overlap syndrome) is an extremely rare autosomal recessive disorder that combines features of two distinct DNA repair conditions: xeroderma pigmentosum (XP) and Cockayne syndrome (CS). This overlap syndrome arises from mutations in genes involved in nucleotide excision repair (NER), most commonly XPB (ERCC3), XPD (ERCC2), and XPG (ERCC5). Because these gene products play roles in both transcription-coupled and global genome NER pathways, mutations can produce the combined phenotype. Patients typically present in infancy or early childhood with the hallmark sun sensitivity and freckling of xeroderma pigmentosum, along with a markedly increased risk of ultraviolet-induced skin cancers including melanoma, squamous cell carcinoma, and basal cell carcinoma. Simultaneously, they develop features characteristic of Cockayne syndrome, including progressive growth failure (dwarfism), microcephaly, intellectual disability, progressive neurological deterioration with sensorineural hearing loss, retinal degeneration (pigmentary retinopathy), cataracts, and characteristic facial features sometimes described as a cachectic or bird-like appearance. The neurological involvement tends to be progressive and debilitating, affecting both the central and peripheral nervous systems. There is currently no cure or disease-modifying therapy for XP-CS complex. Management is supportive and multidisciplinary, focusing on rigorous sun protection (including UV-blocking clothing, sunscreen, and environmental modifications) to reduce skin cancer risk, regular dermatological surveillance with early excision of skin malignancies, ophthalmological monitoring, hearing aids for sensorineural hearing loss, nutritional support for growth failure, and neurological and developmental support. Prognosis is generally poor, with many patients experiencing significant morbidity in childhood due to the combined effects of neurodegeneration and cancer predisposition, and life expectancy is often significantly shortened compared to either condition alone.

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