Xeroderma pigmentosum in Adult
Patients with XP present within the first several years of life with UV-induced changes including lentigines, dyspigmentation, and xerosis. These patients later develop squamous cell carcinomas (SCCs), basal cell carcinomas (BCCs), melanomas, and ocular tumors at significantly increased rates. Progressive neurologic degeneration is present in 20%-30% of patients with variable severity.
Patients may have mutations that result in defective global genome repair (GGR) or both GGR and transcription-coupled repair (TCR). When only GGR is defective, there is milder skin involvement and no neurologic abnormalities. There are 8 known complementation groups associated with XP, each with distinctive genetic loci and phenotypic variants:
XPA – DDB1 protein, common in Japan
XPB – ERCC3 gene, associated with Cockayne syndrome and trichothiodystrophy
XPC – Endonuclease, most common in the United States, no neurologic sequelae
XPD – ERCC2, associated with trichothiodystrophy and XP-Cockayne complex
XPE – only GGR defect, thus mild phenotype, no neurologic sequelae
XPF – More common in Japan, only GGR defect, no neurologic sequelae
XPG – Very rare, associated with Cockayne syndrome
XPV – 30% of all cases, no neurologic sequelae
Cockayne syndrome and trichothiodystrophy are also disorders of nucleotide excision repair and usually result in neurodegeneration; however, patients with XP may exhibit overlapping phenotypic features of both syndromes.
Early diagnosis and vigilant sun protection can reduce the morbidity associated with this disease. Compliance with sun-protective measures and lifestyle modifications can have psychosocial implications. Overall, life expectancy with XP is dependent on phenotype and level of photoprotection.
Q82.1 – Xeroderma pigmentosum
44600005 – Xeroderma pigmentosum
- Erythropoietic protoporphyria (EPP) – Can have similar clinical features to XP with photosensitivity beginning in childhood. Definitive diagnosis can be gained from erythrocyte porphyrins, or late changes can be diagnosed via skin biopsy.
- Congenital erythropoietic porphyria (CEP) – Infants will have extreme photosensitivity and dark urine. Patients will have elevated uroporphyrin I and coproporphyrin I.
- Bloom syndrome – Photosensitivity with short stature, characteristic facies.
- Cockayne syndrome – Can have overlap syndromes as mentioned above. Characterized by dwarfism and beaked nose but will lack key features of XP including freckling and skin cancer.
- Rothmund-Thomson syndrome – Photosensitivity with poikiloderma. Will lack freckling and skin cancer as seen in XP.