Xeroderma Pigmentosum Overview

Xeroderma pigmentosum (XP) is a rare autosomal recessive disorder of DNA repair characterized by extreme photosensitivity and markedly increased risk of skin cancer. Affected individuals show severe burning and blistering with minimal sun exposure, followed by premature aging and numerous skin cancers. The condition results from defects in nucleotide excision repair (NER), preventing removal of UV-induced DNA damage. Individuals with XP require comprehensive sun protection and intensive skin surveillance to detect and treat skin cancers early. This devastating condition dramatically limits outdoor activity and normal childhood activities, requiring extensive family support and adaptation.

Clinical Features and Presentation

XP presents with extreme photosensitivity manifesting as severe burning, erythema, and blistering with minimal sun exposure, often appearing after just minutes in the sun. Affected individuals develop freckling and poikiloderma (irregular pigmentation) in sun-exposed areas during childhood, even with careful sun protection. Progressive xerosis (dryness) and atrophy develop on sun-exposed skin. Photophobia and ocular involvement including progressive keratitis are common. Premature aging of sun-exposed skin is characteristic and striking. The incidence of skin cancers is dramatically increased, with many XP patients developing multiple melanomas and nonmelanoma skin cancers by the second or third decade of life. Some patients develop hundreds of skin cancers by adulthood. Disease severity varies; some patients show earlier and more aggressive skin cancer development than others.

Neurological Involvement and Complications

Neurological features occur in 20-30% of XP patients, representing a more severe phenotype with significantly worse prognosis. Progressive neurological decline includes progressive hearing loss, progressive ataxia (loss of coordination), and cognitive decline. The mechanism of neurological involvement is incompletely understood but relates to accumulation of DNA damage in the central nervous system due to defective NER. Progressive neurological disease may eventually result in wheelchair dependence and severe disability. Some patients develop peripheral neuropathy affecting sensation and motor function. The presence of neurological involvement substantially worsens long-term prognosis and quality of life.

DNA Repair Defects and Pathophysiology

XP results from defects in nucleotide excision repair (NER), the primary pathway for removing UV-induced DNA lesions including thymine dimers. Seven genes (XPA through XPG) have been identified in XP, each involved in different steps of NER. These genes encode proteins that recognize damaged DNA, unwind the DNA double helix, excise the damaged segment, and allow DNA polymerase to synthesize replacement DNA. Defective NER in XP patients allows accumulation of UV-induced mutations, causing progressive cell death, cancer initiation, and in some cases, neurological degeneration. Understanding the specific genetic mutation helps predict disease severity and neurological involvement risk.

Diagnosis and Testing

Diagnosis is established through cellular hypersensitivity testing showing impaired DNA repair after UV exposure. Specialized testing measures DNA repair capacity and hypersensitivity to UV-induced cell killing. Genetic testing identifying specific NER gene mutations confirms XP diagnosis and the causative gene variant. Knowing the specific genetic variant helps predict disease severity and complications. Prenatal diagnosis is available through genetic testing of fetal DNA. Carrier screening identifies heterozygous relatives who are unaffected but can pass the mutation to offspring.

Management and Sun Protection

Management centers on aggressive sun protection including protective clothing (UV-protective), broad-spectrum sunscreen with SPF 50+, and limiting sun exposure. Outdoor activity requires complete protective gear. Schools must provide UVA/UVB-filtered or indoor spaces for classes and activities. Most XP patients must remain indoors during daylight hours, attending school and work in evening or night shifts. This dramatic lifestyle limitation creates significant psychosocial burden. Dietary antioxidants and experimental protective agents may have modest protective effects but cannot substitute for sun avoidance. Regular dermatologic surveillance with examination and photography aids early skin cancer detection. All suspected skin cancers require prompt biopsying and treatment.

Frequently Asked Questions

Can my child go outside? Outdoor activity requires complete sun protection including protective clothing and high-SPF sunscreen, and is best limited to early morning, late evening, or completely avoided.

Will my child develop cancer? Dramatically increased cancer risk (estimated 10,000-fold higher than general population) necessitates close surveillance and early intervention.

How is XP diagnosed? Cellular hypersensitivity testing and genetic testing confirm diagnosis.

Is there treatment? No cure exists; management focuses on sun protection and cancer surveillance.

What about neurological disease? Approximately 20-30% of XP patients develop progressive neurological disease; regular neurological monitoring is essential.

References

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  3. Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 6th ed. Elsevier; 2016.
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