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 the development of cutaneous melanoma (CM). Sun exposure seems to increase the number of MN. This study was designed to determine the influence of genetic and environmental factors on the development of MN. In November 1992, moles were counted by a dermatologist in 20 monozygotic (MZ) and 20 dizygotic (DZ) twins (Budapest, Hungary). All MN were recorded in a schematic figure and classified according to size, colour and clinical criteria of atypia. All subjects completed a standard questionnaire 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) of MN ≥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 (≥ 2- < 5 mm) (p < 0.01), total nevus count for large (≥ 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 environmental factors. Laterality correlations of MN counts on the arms within and between monozygotic twins showed a positive trend regarding the influence of environmental factors. We could not find a significant correlation between sun exposure history (childhood, adolescence) and the number of pigmented lesions. In summary, there is a significant genetic influence on the incidence of benign melanocytic lesions ; the association with environmental influences, especially ultraviolet rays, requires further investigations.