Hair loss, or androgenetic alopecia, is believed to be inherited from either parent, not just the maternal side. The cause of hair loss is still not well understood, but research is ongoing to identify the responsible genes.
Hair loss is a condition in which hair, usually on the crown of the head, begins to fall out and stops growing back completely. The most common type is referred to as male pattern baldness, or more technically as androgenetic alopecia, where the hair thins out until it disappears from the head. While it was long believed that this condition was inherited from the maternal side of the family, researchers now think it’s likely that any genetic factors could come from either parent.
Hair grows on the head from a number of different hair follicles. The average person has around 100,000 follicles, each of which can grow somewhere around 20 distinct hairs over the course of a person’s lifetime. When these follicles stop producing hair, the most common types of hair loss occur.
For years, hair loss was thought to be inherited from the maternal side of the family. Some studies have suggested that it is caused by the presence of excess androgen receptors on the scalp. This has been seen as the result of a genetic difference, causing more androgen receptors to form, or those that are formed to be more stable and less susceptible to breakdown.
The androgen receptor gene resides on the X chromosome, which men inherit from their mothers. As a result, the tendency to lose hair in certain ways was thought to be passed down from the mother and could usually be traced back to the maternal grandfather. If the maternal grandfather lost his hair, folk wisdom holds, the grandchild will too.
The truth, however, appears to be that hair loss is inherited no more often from the mother than from the father. The amount of data available on the matter is surprisingly sparse, with most of the evidence for inheritance through the maternal side coming from a 1916 study with fairly shaky methodology. Current genetics is not well understood. Androgen receptor genes appear to be a somewhat simplistic explanation, and they don’t necessarily hold up to large sample size studies.
The data now appears to show that whatever the cause or causes of hair loss in men, they have certain characteristics that people can be fairly certain of. First, because of the range of people who lose their hair and the correlations between father-son and maternal-grandparent-grandchild baldness, it appears that the genes responsible are actually autosomal, residing neither on the X nor the Y chromosome. It also appears that genes have variable penetrance, since siblings do not necessarily have the same frequency of hair loss. The genes responsible also appear to be dominant and not recessive as once thought.
It is surprising that such a frequently discussed issue has so little data available. In recent years however, especially after the mapping of the genome, larger studies on hair loss in men have begun. While still inconclusive, it is likely that within the next few years the responsible genes will finally be identified and researchers may be able to say once and for all whether the mother or the father is more responsible for passing on the gene.
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