Xeroderma pigmentosum (XP) is a rare autosomal recessive disease (frequency, one to four per million) in which affected individuals exhibit sun sensitivity, cutaneous pigmentary abnormalities, and a high incidence of skin cancer.1-4 In addition, some patients with XP have neurologic abnormalities such as mental deterioration or sensorineural deafness. The disease is one of progressive and accelerated degeneration of the skin, eyes, and nervous system. Many of these symptoms may be manifestations of repeated environmental insults on a defective DNA repair system.
The earliest cutaneous abnormalities in XP often include an exaggerated sunburn reaction1 and delayed erythema on phototesting.5 Interestingly, some patients with XP tan without this acute photosensitivity reaction.1 However, before 2 years of age, virtually all patients with XP have marked freckling on sun-exposed areas. With continued sun exposure, a poikilodermatous appearance develops in the skin, showing areas of increased pigment, decreased pigment, marked atrophy,
Kraemer KH. Xeroderma PigmentosumA Prototype Disease of Environmental-Genetic Interaction. Arch Dermatol. 1980;116(5):541-542. doi:10.1001/archderm.1980.01640290051009