New research shows that heredity plays an important role in the likelihood of developing moles. This observation is of interest because a large number of moles is believed to be a risk factor for melanoma.
This study is the first to investigate the role of genetic and environmental factors on the development of moles in adult twins. The results are presented by Veronique Bataille, M.D., Twin Research and Genetic Epidemiology Unit, St. Thomas Hospital, London, and colleagues, in the March 15 issue of the Journal of the National Cancer Institute.
The authors worked with 127 pairs of identical twins and 323 pairs of fraternal twins recruited from the St. Thomas U.K. Adult Twin Register. All twins were Caucasian females, aged 18 through 72 years. Each participant completed a detailed sun exposure questionnaire and underwent a standardized skin examination, during which the numbers of moles and freckles were recorded.
The mean number of moles was 35, a number that decreased with age. Fifty-five percent of the twins had fewer than 25 moles, and 22% had more than 100. Identical twins were more likely to have similar mole counts (correlation 83%) than were fraternal twins (correlation 51%), demonstrating the importance of genetic factors in the expression of moles. For younger twins (less than 45 years old), 36% of the variation in the total mole count was attributed to genetic factors, with the remaining variation in mole count attributed to environmental factors. In older twins (45 years or older), environmental effects on total mole count became negligible, with 84% of the variation in mole counts attributed to genetic factors.
Freckles are associated with a fair skin type, which is also a known risk factor for melanoma. The authors found freckle counts to be under strong genetic control (91% heritable).
According to the authors, their study showed that genetic factors are important in the expression of moles and that these factors become more important as age increases. Sun exposure also affects the heritability estimates of moles. Estimates of a genetic component were larger for moles on sun-protected skin compared with sun-exposed areas of the skin. The authors note that studying the relative contribution of genes and environment in the expression of moles at different body sites may help in the future to uncover genes important in melanoma. However, they add that the results of this study highlight the need to account for age and site of mole counts in future genetic linkage or association studies.
Contact: Claire Barber, St. Thomas Hospital, London, 171-922-8120; fax: 171-633-0347.
Note: This memo to reporters is from the Journal staff and is not an official release of the National Cancer Institute (NCI) or Oxford University Press (OUP) nor does it reflect NCI or OUP policy. In addition, unless otherwise stated, all articles and items published in the Journal reflect the individual views of the authors and not necessarily the official points of view held by NCI, any other component of the U.S. government, OUP, or the organizations with which the authors are affiliated. Neither NCI nor any other component of the U.S. government nor OUP assumes any responsibility for the completeness of the articles or other items or the accuracy of the conclusions reached therein.
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