Answer:
Xeroderma pigmentosum: a rare, systemic genetic disease transmitted by a sex-linked recessive gene. It is characterized by extreme sensitivity to sunlight from an early age. Associated metabolic abnormalities include elevation of serum copper and gamma globulin levels, increased excretion of urinary amino acids and decreased excretion of 17-ketosteroids and 17-hydroxycorticosteroids. Beginning in early childhood, affected individuals show an unusual sensitivity to sun exposure with diffuse freckling initially followed by progressive drying and thinning of the skin. Keratoses later appear and by early adulthood, malignant changes in the skin occur in the form of basal cell carcinoma, squamous cell carcinoma, or melanoma. Most individuals eventually die from metastatic skin cancer, though a few cases of long-term survival have been reported. Increased survival has been reported by following a strict management regime consisting of absolute protection from sun exposure, frequent and regular skin observation, and early aggressive treatment of skin tumors as they occur.