Xeroderma Pigmentosum: UV Sensitivity and Cancer Prevention
Xeroderma Pigmentosum (XP) is a rare, autosomal recessive disorder characterized by extreme sensitivity to ultraviolet (UV) light and a significantly increased risk of skin cancer. Due to a defect in nucleotide excision repair, patients with XP are unable to effectively repair UV-induced DNA damage, leading to early onset of cutaneous malignancies and other complications.
Topics: XP, genodermatosis, DNA repair
Overview / Definition Xeroderma Pigmentosum (XP) is a genetic disorder resulting from mutations in genes responsible for the nucleotide excision repair (NER) pathway, which is crucial for repairing DNA damage caused by UV radiation. Patients with XP display a heightened sensitivity to sunlight, leading to a range of clinical manifestations, primarily skin cancers, at an early age. Epidemiology XP is an extremely rare disorder, with an estimated incidence of 1 in 250,000 to 1 in 1,000,000 live births in the general population. The prevalence is higher in certain populations, particularly in regions with a high rate of consanguinity, such as North Africa and Japan. More common in individuals of North African and Japanese descent. Approximately 8 different complementation groups (XP-A to XP-G) have been identified. Patients often present in childhood, typically before the age of 10. Pathophysiology / Mechanism The pathophysiology of XP is rooted in defects in the nucleotide excision repair mechanism, which normally recognizes and removes UV-induced DNA lesions, including pyrimidine dimers. Mutations in the XP genes impair this repair process, leading to: Accumulation of DNA damage due to UV exposure. Increased risk of mutations and, consequently, malignancies. Multiple genes involved, including XP-A, XP-B, XP-C, XP-D, XP-E, XP-F, XP-G, and XP-V, each affecting different aspects of the NER pathway. Clinical Presentation Patients with XP typically exhibit the following clinical features: Photophobia and severe sunburns upon minimal UV exposure. Development of freckles and pigmented lesions on sun-exposed areas, including the face, neck, and arms. High incidence of skin cancers (basal cell carcinoma, squamous cell carcinoma, and melanoma) by the age of 20. Possible neurological manifestations in some XP types, including progressive neurological decline in XP-C and XP-D. Diagnosis / Workup The diagnosis of XP is primarily clinical but can be confirmed through genetic testi