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A genetic test for androgenetic alopecia: polymorphisms in the androgen receptor gene provide a genetic screening test for androgenetic alopecia and earlier medical intervention

Introduction Although the comprehensive details of genetic inheritance for androgenetic alopecia (AGA) are not yet characterized, prevailing evidence supports a polygenic model based primarily on the fact that autosomal and single gene inheritance theories are not supported by observed patterns. Evidence against an autosomal pattern is the observed phenotypic prevalence of AGA in families, which does not fit the expected bimodal distribution. A single gene hypotheses would yield an expected prevalence of around 1:1000, far less than the high percentage of affected males seen in population studies. Efforts to identify the involved genes have focused on those known to be related to mechanisms of hair growth. However, tests failed to reveal any association between the suspect genes and AGA, with one notable exception. There have been four published studies involving over 2,900 patients that document the association between AGA and the androgen receptor (AR) gene on the X chromosome. A particular polymorphism or variant allele at the AR site has been shown to be associated with a higher risk of developing AGA (>60%) and, conversely, a protective, less frequent allele has been associated with a very low likelihood of developing AGA (>85% probability of not developing AGA). In order to assess the usefulness of this finding, we must first distinguish between what is meant by a “screening test” versus “diagnostic test.” The advantages of a screening test to identify a high-risk population for AGA, prior to visible signs of hair loss, for the purpose of early medical intervention will be discussed.