Clinical characteristics: Xeroderma pigmentosum (XP) is characterized by:

1. Acute sun sensitivity (severe sunburn with blistering, persistent erythema on minimal sun exposure) with marked freckle-like pigmentation of the face before age two years;

2. Sunlight-induced ocular involvement (photophobia, severe keratitis, atrophy of the skin of the lids, ocular surface neoplasms);

3. Greatly increased risk of sunlight-induced cutaneous neoplasms (basal cell carcinoma, squamous cell carcinoma, melanoma) within the first decade of life.

Approximately 25% of affected individuals have neurologic manifestations (acquired microcephaly, diminished or absent deep tendon stretch reflexes, progressive sensorineural hearing loss, progressive cognitive impairment, and ataxia). The most common causes of death are skin cancer, neurologic degeneration, and internal cancer. The median age at death in persons with XP with neurodegeneration (29 years) was found to be younger than that in persons with XP without neurodegeneration (37 years).

Diagnosis/testing: The diagnosis of XP is established in a proband on the basis of clinical findings and family history and/or by the identification of biallelic pathogenic variants in DDB2, ERCC1, ERCC2, ERCC3, ERCC4, ERCC5, POLH, XPA, or XPC.

Management: Treatment of manifestations: Premalignant skin lesions such as actinic keratoses can be treated by freezing with liquid nitrogen; larger areas can be treated with field treatments such as topical 5-fluorouracil or imiquimod preparations. Rarely, therapeutic dermatome shaving or dermabrasion has been used; skin neoplasms can be treated (as in persons without XP) with electrodesiccation and curettage or surgical excision; skin cancers that are recurrent or in locations at high risk for recurrence are best treated with Mohs micrographic surgery. Oral isotretinoin or acitretin can prevent new skin neoplasms but have many side effects. Neoplasms of the eyelids, conjunctiva, and cornea can be treated surgically; corneal injury associated with eyelid abnormality can be decreased with eye drops or soft contact lenses; corneal transplantation may improve the visual impairment resulting from severe keratitis. Hearing loss may be treated with hearing aids.

Prevention of primary manifestations: Avoid sun and other UV exposure to the skin and eyes. Measure UV light with a light meter in an affected individual's home, school, and/or work environment so that high levels of environmental UV can be identified and eliminated.

Surveillance: Skin examinations by a physician every three to 12 months; eye exams for signs of UV exposure and damage every six months; routine eye and neurologic examinations for progressive neurologic abnormalities every 12 months; audiograms every six to12 months.

Agents/circumstances to avoid: UV exposure from sunlight and artificial sources of UV radiation; cigarette smoke.

Evaluation of relatives at risk: If family-specific pathogenic variants have been identified, molecular genetic testing of at-risk sibs can permit early diagnosis and rigorous sun protection from an early age.

Pregnancy management: Systemic retinoids (isotretinoin, acitretin) may be used as skin cancer chemopreventive agents. These drugs are known to be teratogenic to a developing fetus and pose a high risk for birth defects. Women of reproductive age who are taking a systemic retinoid must use effective contraception and be monitored with regular pregnancy tests.

Genetic counseling: XP is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an XP-related pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the XP-related pathogenic variants have been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for XP are possible.