P1 FINGER LENGTH RATIOS IN MALE ANDROGENETIC ALOPECIA: EVIDENCE FOR AN INTRA-UTERINE EFFECT OF ANDROGENS?
Birch MP, Messenger AG
Department of Dermatology, Royal Hallamshire Hospital, Sheffield, UNITED KINGDOM

The ratio between the lengths of the second and fourth finger digits (2D:4D) shows sexual dimorphism, being lower in men than in women, and is thought to be determined by in utero exposure to androgens. Differences in 2D:4D ratios between members of the same sex have been linked to a variety of characteristics including reproductive success, aggressive behaviour, athletic prowess and sexual orientation. The aim of this study was to test the idea that in utero exposure to androgens is involved in the aetiology of male androgenetic alopecia (MAGA). We measured 2D:4D ratios on both hands in 132 men, of whom 44 were non-bald (Norwood-Hamilton I or II) and 53 had significant vertex balding (Norwood-Hamilton IV or greater). Mean 2D:4D ratios were similar in non-bald men (Right Hand 0.978 SD 0.049, Left Hand 0.974 SD 0.032) and bald men (Right Hand 0.971 SD 0.055, Left Hand 0.970 SD 0.050). However, in non-bald men aged over 50 (n=19) the 2D:4D ratios (Right Hand 0.992 SD 0.053, Left Hand 0.981 SD 0.032) were higher than in non-bald men. The difference was statistically significant in the right hand (t test p<0.05) but not in the left hand (p=0.12). It is generally thought that MAGA is due to the post-pubertal effect of androgens in genetically predisposed men. However, although confirmation in a larger study is needed, these results suggest that in utero exposure to androgens may also contribute to the subsequent development of scalp hair loss.