Ultrastructural studies of xeroderma pigmentosum.

Electron microscopic observations of both sun-exposed and sun-protected skin from a black patient with xeroderma pigmentosum (XP) revealed abnormal ultrastructural changes in the melanin pigmentary system, tonofibrillar-desmosome complexes, endoplasmic reticulum, mitochondria, and nucleoli of all keratinocytes. The difference between the cellular changes in the sun-exposed skin and that protected from sunlight was quantitative rather than qualitative in character. The most salient changes were seen in sun-exposed specimens: melanosomes limited by a membrane showed a high degree of polymorphism with a tendency to form large complexes, and many fibroblast-like cells displayed an intense phagocytic activity for melanosomes, the latter finding not previously reported. The present study supports the conclusions of other investigators that XP is a heterogeneous disease. Clarification of the XP entities by continued research may identify the defective gene and lead to methods of correction by the molecular biologist.