The inheritance of common baldness: two B or not two B?

Kuster W, Happle R.

So far, it is a widely accepted opinion that androgenetic alopecia is caused by an autosomal dominant gene with reduced penetrance in women.

This view is essentially based on a family study performed by Osborn in 1916. She believed that balding men would be either heterozygous (Bb) or homozygous (BB), whereas balding women would be homozygous (BB).

By contrast, we here present five arguments favoring a polygenic inheritance of the trait:

(1) the high prevalence of the trait,

(2) the distribution of balding patterns in the general population along a gaussian curve of variation,

(3) the fact that the risk increases with the number of relatives already affected,

(4) the slightly increased risk of relatives of severely affected women as compared to the relatives of mildly affected women, and

(5) the fact that a predisposition inherited from an affected mother is of greater importance than that inherited from an affected father.

In conclusion, the simple mendelian model of Bb and BB can no longer be upheld.