What are the genetics of male pattern baldness? originally appeared on Quora: the knowledge sharing network where compelling questions are answered by people with unique insights.

Answer by Adriana Heguy, Director of the NYUMC Genome Technology Center and Professor of Pathology, on Quora:

Unfortunately the genetics of androgenetic alopecia (male-pattern baldness) is not really well understood. The more complex the biology behind a phenomenon is, the more difficult is going to be to find all the genetic factors. Regulation of hair growth in mammals is extremely complicated and poorly understood, in spite of this subject being a very active area of research. Hair is very important to mammalianthermoregulation thus it makes sense for its biology to be very complex.

It is clear that male-pattern baldness is a highly heritable condition [1], although there is also some evidence for the involvement of epigenetic factors [2]. There are a few genes implicated in androgenetic alopecia from different studies [3]. Unsurprisingly, the androgen receptor (AR) gene is one of them, as it is well known that the condition is dependent on testosterone (an androgen). The androgen receptor is on the X chromosome, which is why some people propagate the myth that male-pattern baldness comes from the mother's side of the family (a male inherits the X chromosome from mom, the Y chromosome from dad). But it is not the only gene involved, or even the main gene involved. There are genes in basically all chromosomes that have been implicated in androgenetic alopecia, and this is what makes it so difficult to unravel, as we would have to examine the overall contribution that each gene variant (single nucleotide polymorphism, or SNP) play in hair loss, and also how these genes interact with each other and the environment to result in the phenotype.

Position of genes implicated in male pattern hair loss, from [4].

Some of these genes code for transcription factors or histone deacetylases. TheWnt pathway appears to be involved. Even though we know a fair amount about transcription factors, the Wnt pathway, etc., this still does not tell us much about what's actually going on in androgenetic alopecia and why the hair follicles shrink and die. The hope is that identifying these genes will provide targets for therapeutic intervention. But so far, we are still far from a definitive "cure" for androgenetic alopecia.

If there is any consolation for men (or at least, heterosexual men) distressed about hair loss, if it was a phenotype that was repulsive to females, the gene variants would have been weeded out a long time ago, by sexual selection. Many of us find bald heads very manly and attractive.

Footnotes

[1] Genetic basis of male pattern baldness.

[2] Eleven pairs of Japanese male twins suggest the role of epigenetic differences in androgenetic alopecia.

[3]Hunting the genes in male-pattern alopecia: how important are they, how close are we and what will they tell us?

[4] Hunting the genes in male-pattern alopecia: how important are they, how close are we and what will they tell us?

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The Unpredictable Genetics Of Male-Pattern Baldness

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