Phenotypic variation in the familial atypical multiple mole-melanoma syndrome (FAMMM).

The familial atypical multiple mole-melanoma syndrome (FAMMM) is characterised by an autosomal dominantly inherited susceptibility to multiple atypical moles which show variable colouration ranging from black to brown, tan, red, or pink, with occasional variegation. These compound naevi may be macular or papular, with regular or irregular borders, and measure 1 cm or more in size. They may be few in number or absent or may exceed 100 in a given patient. They are located predominantly on areas not exposed to the sun. Dysplastic changes in melanocytes, fibroplasia, focal chronic inflammatory cell infiltrate, and new blood vessel formation of the papillary dermis characterise their histopathology. These findings are not uniformly present. Because of these distinctive features, coupled with their propensity for transformation to cutaneous malignant melanoma, little attention has been given to the possibility of either minimal or absent cutaneous expression of the phenotype or more diverse neoplastic involvement in this disease. These latter phenomena, which we ascribe to the pleiotropic effects of the cancer-prone FAMMM genotype, were observed in a single FAMMM kindred, the subject of this report.