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Genes as the cause
Hereditary hair loss
Both men and women can inherit the genes for hair loss from the maternal side as well as from the paternal side of the family. The effect of these genes depends on androgens, so that ordinary hair loss is called androgenetic alopecia or constitutional hair loss (the same expression is used for hair loss among men).
Androgenetic hair loss can only arise if certain constitutional (inherited) genes exist. Genes are generally referred to as a hereditary disposition or hereditary factor because they are the carriers of genetic information which is passed on to descendants through reproduction. The expression – i.e. the manifestation or the activity status of a gene – is precisely regulated in every cell. A gene is a segment of deoxyribonucleic acid (DNA).
Every person has 23 chromosome pairs, i.e. 46 chromosomes. Chromosomes are structures which contain genes and therefore genetic information. The genetics of androgenetic alopecia is complicated, and hair loss seems to concern more than one gene. If several genes dominate a characteristic, it is said to be polygenetic.
Whereas the chromosomes of a chromosome pair normally look the same, the 23rd chromosome pair is an exception. The genes located on the X or Y chromosomes are sex-determining. The genes of the other 22 chromosome pairs are autosomal, i.e. they are not involved in the determination of sex. It is assumed that the genes which determine androgenetic alopecia are autosomal – i.e. that hair loss can be inherited from the maternal or paternal side. The universally valid opinion, that hair loss is only inherited from the maternal side of the family is erroneous. Due to reasons not yet entirely clarified, the susceptibility to hair loss is greater if the father is affected by this.
“Dominant” means that only one gene of a pair is necessary in order to exhibit the characteristic in an individual. “Recessive” means that both genes are necessary in order to express a characteristic. It is assumed that the genes responsible for androgenetic alopecia are dominant.
Just because a person carries genes for hair loss or baldness does not mean that this characteristic will be exhibited. The ability of a gene to express characteristics in a certain individual is called expression. It depends on quite a few factors. The most important of them are hormones and age, but stress and other factors can also play a role. In one simple example this means that a man whose father and grandfather are bald or suffer considerably from hair loss can himself be affected little or not at all by this; either because the genes for this have not been inherited or because the expression of the inherited and responsible genes is restricted.
It is interesting that to this day none of those genes which are responsible for male hair loss could be identified. It can be concluded that any type of genetic manipulation as help for avoidance of hair loss is still a long way in the future.