Café au lait spots in ataxia-telangiectasia (A.T.). Histochemical and ultrastructural study in one case.

Café au lait spots appear to represent one of the cutaneous features of Ataxia-telangiectasia (A.T.). At the cellular level, they are characterized by an epidermal hypermelanosis with a normal number of melanocytes. At the subcellular level, two basic abnormalities are observed: (1) an increase in the synthesis of melanosomes; (2) a modification of their distribution within the epidermal keratinocytes. Numerous pendulous melanocytes project into the upper dermis. Altered melanocytes are also observed. These show mitochondrial dilatation, melanosomal autophagic vacuoles, as well as lipid droplets. These abnormalities are not observed in the normal surrounding skin. The significance of these observations is discussed and stress is placed on the difficulty in establishing a differential diagnosis of café au lait spots, based on their histoenzymological and ultrastructural features.