Genetics of androgenetic alopecia

Androgenetic alopecia (AGA, male pattern baldness [MIM 109200; MIM 300710; MIM 612421]) is the commonest form of hair loss in humans, and the its prevalence is highly age-dependent. Eight percent of European men above the age of 70 are affected by AGA, but only 30-40% of women. In many affected individuals, particularly women, AGA causes clinically significant psychological distress. Hair loss is attributable to an altered hair cycle and miniaturization of the hair follicles. The pathogenesis is androgen dependent, and genetic predisposition is an essential pre-requisite of the phenotype. Several studies have identified the androgen receptor (AR)/ectodysplasin A2 receptor (EDA2R) locus on the X-chromosome as the strongest contributing factor. Genome wide association studies have identified a further locus on chromosme 20p11. The neares scalp expressed gene to the association signal is paired box 1 (PAX1). Although there is no obvious connection between PAX1 and the androgen signalling pathway, the pathophysiological processes underlying the association signal for chromosome 20p11 have not yet been explained. At best, currently available therapies for AGA permit the arrest of hair loss. The identification of AGA associated genes and the elucidation of their function will gradually reveal the biological causes of AGA and offer hope for the development of new therapies.