A STUDY OF HUNGARIAN TWINS INVOLVING THE INFLUENCE OF GENETIC AND ENVIRONMENTAL-FACTORS ON BENIGN, MELANOCYTIC LESIONS

Multiple, benign, melanocytic nevi (MN) are a major risk factor for th e development of cutaneous melanoma (CM). Sun exposure seems to increa se the number of MN. This study was designed to determine the influenc e of genetic and environmental factors on the development of MN. In No vember 1992, moles were counted by a dermatologist in 20 monozygotic ( MZ) and 20 dizygotic (DZ) twins (Budapest, Hungary). All MN were recor ded in a schematic figure and classified according to size, colour and clinical criteria of ''atypia'' All subjects completed a standard que stionnaire for sun exposure history. Standard intrapair correlations, heritability and laterality correlations in MZ twins were calculated. In MZ twins, the total nevus count correlated significantly (p < 0.005 ). In contrast, there was only a significant correlation (p < 0.001) o f MN greater than or equal to 2 mm with irregular borders in DZ twins. The difference between standard intrapair correlations for MZ and DZ twins was significant regarding the total nevus count for all MN (p < 0.05), total nevus count of ''small'' common MN (greater than or equal to 2- < 5 mm) (p < 0.01), total nevus count for large (greater than o r equal to 5 mm) MN (p < 0.01) and with irregular borders (p < 0.01). Heritability was calculated at around 60%, thus 40% may be linked to e nvironmental factors. Laterality correlations of MN counts on the arms within and between monozygotic twins showed a positive trend regardin g the influence of environmental factors. We could not find a signific ant correlation between sun exposure history (childhood, adolescence) and the number of pigmented lesions. In summary, there is a significan t genetic influence on the incidence of benign melanocytic lesions; th e association with environmental influences, especially ultraviolet ra ys, requires further investigations.