INFLUENCE OF SUN EXPOSURE AFTER CHILDHOOD ON THE DEVELOPMENT OF NEVI - A STUDY IN MONOZYGOTIC TWINS

Childhood has been shown to be a crucial period for the effect of sun exposure on the development of melanoma and melanocytic nevi. Whether or not sun exposure after childhood still promotes the genesis of nevi is sti II unclear. Theoretically, adult monozygotic twins represent a perfectly controlled model to answer this question. Twenty eight pair s of monozygotic twins over 30 years of age were examined and question ed about their sun exposure. As expected there was good intrapair corr elation for nevus density. However most twins exhibited at least a 20% difference in the number of nevi, which can be attributed to a differ ent exposure to environmental factors after childhood. Within a pair, the twin who was more sun-exposed between 15 and 30 years of age had a twice higher risk of having more nevi. The shows that the influence o f sun exposure on the development of nevi is not limited to the first years of life. Intrapair differences in the number of nevi on never-ex posed areas raises the possibility of either a systemic effect of sun exposure or other yet unidentified environmental risk factors for the development of nevi.