by Kevin Rands | October 24, 2016 5:42 pm
So exactly where is hair loss inherited from? Mother’s father like they tell us? An unpredictable unorganized appearance throughout family members? Dr. Richard Lee addresses the genetics of hair loss, and gives the solid scientific answer to this age old question.
Dr. Ken Washenik, medical director of the Aderans Research Institute, has an amusing and straightforward retort to alopecia androgenetic patients who tell him that there is no history of MPB in their family. He simply says, “Now there is”.
Unquestionably, the two most important factors in the etiology of the common patterned loss of scalp hair known as male pattern baldness (MPB) are the genetic predisposition and the dependence on androgens. Without both components, MPB does not occur. Whereas the hormones involved in MPB (primarily testosterone and dihydrotestosterone) have been identified, the inheritance of MPB remains only partially solved.
It’s an enduring and common misconception among patients that Male Pattern Baldness is ‘inherited from the mother’s side’. Well, that statement is neither right nor wrong. Pattern baldness can be inherited from the mother’s side. But it can also be inherited from the father’s side. Despite the universal interest in the genetics of Male Pattern Baldness, there is a surprisingly small number of scientific studies in regards to the genetics of Male Pattern Baldness and there is only one known extensive family study on Male Pattern Baldness. This study of hair growth patterns in 22 families concluded that common pattern baldness was an autosomal dominant phenotype in men and an autosomal recessive phenotype in women. However, the validity of these results are controversial because of a lack of details regarding examination methods and sampling errors of this study, which was published in 1916.
Despite the fact that the entire human genome, comprising approximately 30,000 genes in the human DNA, was completely mapped out as of April 2003, the gene or, more likely, genes responsible for MPB, have not been identified. Studies of the genes (on chromosome Xq11.2^q12) encoding the two 5alpha-reductase isoenzymes show that they are not the genes associated with male pattern baldness.
What is known is that the age of onset, the rate of progression, and the pattern of follicular miniaturization are all influenced by heredity. Generally, the earlier the onset of balding, the more extensive the degree of hair loss will eventually be.
There are often times when an accelerated rate of progression of MPB will coincide with some other event, such as a change in medication, or the onset of another medical disorder, or a change in habits, etc. Although these events may cause hair loss, they do not precipitate or aggravate MPB.
A study examining 410 men with premature baldness found evidence of a genetic influence from the father’s side in only 236 cases. Hair loss similarities between father and son have also been observed in another study in regards to the frequency of MPB in brothers of men having prematurely bald fathers (66%) compared with brothers of men with unaffected fathers (46%). The relatively strong association of MPB between fathers and sons in this study was not consistent with a simple Mendelian autosomal or sex-linked dominant inheritance and suggested that several genes (a polygenic etiology) may be responsible for MPB. As further evidence against a single and/or X-linked gene being responsible for MPB is the observation that only 33% of the fathers of 18 women suffering from severe pattern baldness also had MPB. These findings suggest that other autosomal genes play an important role in the expression of MPB.
Considering the high proportion of men affected by MPB, its distribution in the general population, the increased risk of MPB as the number of affected close relatives increases, and the high risk of inheritance from either or both affected parents, one can support a strong argument in favor of a polygenic inheritance.
It seems ironic that with all the knowledge that has been accumulated in regards to MPB in the past several decades, we still do not know the exact genetic inheritance of MPB. What is known is that the genes are autosomal (not on the X or Y chromosomes), dominant (as opposed to recessive), and have variable penetrance (so it may not affect siblings of the same parents to the same degree).
References:
Ellis JA, Stebbing M, Harrap SB: Genetic analysis of male pattern baldness and the 5alpha-reductase genes. J Invest Dermatol. 110(6):849-53, 1998
Harris H: The inheritance of premature baldness in men. Ann Eugenics 13:172-181, 1946
Neale MC, Cardon LR: Methodology for Genetic Studies in Twins and Families. NATO ASI Series. Dordrecht: Kluwer Academic Publishers, 1992
Kuster W, Happle R: The inheritance of common baldness: Two B or not two B?
J Am Acad Dermatol 11:921-926, 1984 Salamon T: Genetic factors in male pattern alopecia. In Baccaredda-Boy A, Moretti G, Frey JR (eds): Biopathology of Pattern Alopecia. New York, Karger, pp 39-49, 1968
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