Hair Foundation
Genetics of Female Androgenetic Alopecia

Hair loss is typically thought to only afflict males, however the reality is women constitute forty percent of hair loss sufferers in the U.S. Female pattern hair loss (androgenetic alopecia) is an emotionally devastating condition and 50% of women suffer from some degree of hair loss by the age of 60. The most common form of hair loss in women, androgenetic alopecia, occurs in women that are genetically predisposed. Like any medical condition, early detection is the best practice for prevention.

The cause of female hair loss is often elusive and at times misdiagnosed. Androgenetic alopecia is the most common form hair loss in both males and females, and appears to follow a polygenetic inheritance pattern (many genes are involved in the cause of hair loss). Strong genetic markers have been identified for this form of hair loss. In particular, certain variations in the androgen receptor have been associated with a higher risk for developing female pattern hair loss. Furthermore, these androgen receptor variations have been correlated with elevated plasma testosterone and androgen (male sex hormones) levels in women. These androgens have a profound affect on hair loss and are the basis for certain hair loss treatments.

One marker that can assess the risk for female androgenetic alopecia is a variation in the androgen receptor (AR) gene. Individuals have a variable length CAG repeat in the AR gene. Differences in the number of CAG repeats affect the AR sensitivity to androgens. A shorter CAG repeat is associated with a higher risk for female androgenetic alopecia, conversely a longer repeat is associated with a lower risk for female androgenetic alopecia. Furthermore, one study of a female population found that for a CAG repeat length of 15 or less, 97.7% suffered from moderate to severe hair loss (Ludwig Type II and III). Similarly, among women with androgenetic alopecia only 2.3% had a CAG repeat length over 23. This marker for female androgenetic alopecia provides women with their CAG repeat score and allows them to compare their results to the current scientific literature.

The medical diagnosis and prediction of female pattern hair loss remains a challenge that was met with limited success. Unlike male pattern hair loss, "pattern distribution" is not typical for most women with androgenetic alopecia. Hair loss in women typically occurs with diffuse thinning without a defined pattern. Often the frontal hair line is intact, but behind this the scalp becomes visible in the midline. Progressive thinning over time may extend back to the crown area, and often impacts areas on the sides and back of the head, leaving the scalp covered with diffusely thinning hair, but usually no bare areas. Because of this lack of a defined pattern one cannot distinguish female pattern hair loss from other causes of hair loss just by looking at it. It is important to exclude other causes of hair thinning, which can mimic androgenetic alopecia in women, for selection of the most beneficial hair loss therapy.