Hair Loss (PDF)

inheritance pattern of AGA is still debated. It is believed to be most likely autosomal dominant, polygenic, and inherited from either parent. The gene frequency appears to be most common in Caucasians, less so in Africans, and least frequent in Amerindians, Asians and Inuits. The McKusick Mendelian Inheritance in Man (MIM) number for AGA is 109200. A MIM entry that begins with the number one indicates an autosomal dominant inheritance.

Some previous work on the genetics of AGA dates back to 1919. Osborn22 stated that AGA was a sex-limited autosomal dominant trait similar to the inheritance of horns in sheep. She believed that men could be either homozygotes (BB) or heterozygotes (Bb), and women who presented with AGA were homozygotes only. Smith and Wells23 have hypothesized that the expressivity of the gene might be partly determined by the androgen level: the genotype BB may lead to the clinical picture of AGA even at low androgen levels in women, whereas the genotype Bb requires higher amounts of androgen. The genotype bb may remain sub-clinical in both sexes. Harris24 found that of 117 men with AGA, 66% of the brothers were bald if the father of the proband was also bald, and 46% of the brothers were bald if the father was not bald. Fifty-six per cent of bald men had bald fathers. The authors concluded that this was consistent with an autosomal dominant gene. Salomon25 felt that AGA is inherited through multifactorial or conditioned dominance via an autosomal dominant gene of variable expressivity. He studied 119 males with AGA. Sixteen had no family history, 65 had two generations, 24 three generations and 3 four generations involved. Eleven had two generations of families with both parents affected. There was an association of increasing amounts of chest hair, but not back hair, in affected individuals. This observation is quite interesting, in that Shapiro has noted the same trend in increased body hair distribution in a disproportionately large number of his balding male patients, although no formal study has been performed. A family has been described in which common baldness with early onset occurred in females only.