Genetic and environmental contributions to size, color, shape, and other characteristics of melanocytic naevi in a sample of adolescent twins

The presence of melanocytic naevi is the strongest known risk factor for ma lignant melanoma. We have developed a computer imaging system with which it is possible to make quantitative measures of the size, color, and shape of pigmented lesions. The objective of this study was to examine the genetic and environmental contributions to these characteristics of naevi as measur ed by computer image analysis in a sample of adolescent twins. We captured video images of the 5 most atypical pigmented skin lesions (i.e., the large st, darkest, or most irregularly shaped) on each individual from 322 Austra lian adolescent twin pairs. Features extracted by computer image analysis f or each lesion included color, size, symmetry, elongation, boundary irregul arity, and edge distinctness. We found major genetic influences on the colo r and size of lesions accounting for between 40 and 80% of total variance. There were significant components of shared environmental influence (22-45% of total variance) for the color variables, with sun exposure the most obv ious explanation. Differences between individuals in naevus color and size are largely genetic in origin although there are significant environmental contributions to color as well. (C) 1999 Wiley-Liss, Inc.