Male Pattern Baldness and Your Genes (from 23andMe)

Male pattern baldness, or androgenetic alopecia, occurs when hair follicles begin to shrink. Small follicles give rise to shorter, finer hairs. Eventually a very small follicle is left with no hair inside at all. Male pattern baldness usually proceeds in a familiar pattern: it begins on the crown of the head and/or with a receding frontal hairline, and then progresses rearward.

The importance of male hormones in male pattern baldness is supported by the finding that a variation in the androgen receptor gene can lower the age at which a man starts to lose hair and the degree of baldness.

The androgen receptor responds to signals from male hormones like testosterone and dihydrotestosterone (DHT). It is turned on in hair follicles located on parts of the body that have thick, terminal hair; it is off in follicles that make the wispier, less pigmented vellus hair (i.e. "peach fuzz") which is found all over the body.

The androgen receptor is encoded by the AR gene, which resides on the X chromosome. The influence of this SNP on male pattern baldness is reflected in the common wisdom that baldness is often passed down from mother to son.

A man has only one X chromosome, which he inherits from his mother. So if a man has the baldness-promoting version of the androgen receptor SNP, he must have received it from mom. But his mother got one X chromosome from her mother and one from her father. This means that the baldness SNP could have originated with the man's maternal grandfather.

Another SNP, on chromosome 20, has also been repeatedly associated with male pattern baldness. No one knows yet what gene this SNP is influencing. Research has shown, however, that this SNP acts independently of the androgen receptor SNP on the X chromosome and has no obvious connection to male hormones. More research will be needed to more fully understand how this variation impacts male pattern baldness.

The variations reported here have been shown to have an association with male pattern baldness only in men with European ancestry. Male pattern baldness is relatively uncommon in those of African ancestry; this may be due to the relative rareness of the baldness version of the androgen receptor gene SNP in this population. Studies have shown that male pattern baldness in Asians has been relatively rare in the past, but is approaching the rates seen in those of European ancestry. This suggests that environmental factors such as socioeconomic environment and westernized diet may contribute to baldness.