The Genetic Link

Looking at research into Androgenic Alopecia (AGA) here’s what I found:

Hair follicles in different parts of the human body behave differently throughout the human lifespan. Beard growth is androgen-dependent, while hair sensitive to androgen experiences thinning as result of androgens. [25]

It seems androgens cause beard hair, armpit (axillary) hair and pubic hair follicles to enlarge while frontal and vertex scalp hair decrease is size. Others hair follicles like eyebrows and eyelashes don’t seem to change in size. [28]

Researchers in one study concluded this opposite impact of androgens on hair follicles of the beard and scalp was due “to differential gene expression within hair follicles”. [18] Another study stated the factors behind AGA “to be genetic predisposition coupled with the presence of sufficient circulating androgens” and “require the inheritance of several genes”. [3]

A study published in 2005 summarized the role of genetics with AGA by saying AGA is “androgen dependent, and genetic predisposition is the major requirement for the phenotype.”[9-] In other words, we can define AGA not only as androgen-dependent but also as a genetic condition.

Androgens would have no effect if it wasn’t for androgen receptors (AR’s). AR’s are what enables the human body to respond to androgens, and thus play a crucial role in male sexual development. Genetic variations in the AR gene are more common in men with an early onset of AGA.

German researchers named the androgen receptor gene as the cardinal prerequisite for balding.[9-] They concluded a certain variant of the androgen receptor is needed for AGA to develop. In the same year the results of this study were confirmed by other researchers.[10-]

This gene is recessive and a female would need two X chromosomes with the defect to show typical male pattern alopecia. Seeing that androgens and their interaction with the androgen receptor are the cause of AGA it seems logical that the androgen receptor gene plays an important part in its development.

It is thought by researchers that AR gene alterations (variations or polymorphism) lead to an increased activity of the AR’s in the scalp. [29]

Other research in 2007 suggests another gene on the X chromosome, that lies close to the androgen receptor gene, is an important gene in male pattern baldness. They found the region Xq11-q12 on the X-chromosome to be strongly associated with AGA in males. They point at the EDA2R gene as the gene that is mostly associated with AGA. This finding has been replicated in at least three following independent studies. Other genes involved with hair loss have been found. One of them being a gene on chromosome 3. The gene is located at 3q26.[11-] This gene is also involved in a type of baldness associated with mental retardation. This gene is recessive.

Another gene that might be involved in hair loss is the P2RY5. This gene is linked to hair structure. Certain variants can lead to baldness at birth while another variant causes “wooly hair”.[12-]

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Recent research confirmed the X linked androgen receptor as the most important gene. With a gene on chromosome 20 being the second most important determinant gene (snpedia)

A study published in 2005 entitled “Confirmation of the association between male pattern baldness and the androgen receptor gene” looked at the AR gene variations and confirmed “the previously reported association between MPB and the AR gene”. [14]
It was also discovered that alterations in the AR gene, or in the proximity to the AR gene are associated with the increased risk of AGA. These variations result from “small changes in the number or types of DNA building blocks (base pairs) that make up the AR gene.” [22] [29]

A 2008 study affirmed that “Androgenic alopecia is a highly heritable condition, with heritability estimates of over 80%.” [22]

A more recent study published in June of 2010 agrees with genetic predisposition, it stated “genetic factors and androgens play a major role [in AGA]”. It further stated, “Polymorphism of the androgen receptor gene was first identified in association with androgenetic alopecia.” [20]

The above was written in July 2010

Comment:

The above follows the one line of hair loss research into androgens.Yes, there is a strong genetic component to male pattern baldness, the predisposition is inherited from both parents and involves multiple genes.

Hair loss, even male pattern baldness can and is aggravated and even triggered by other causes besides androgen metabolism and the genes related to such process or androgen receptors.

Edited: 12/30/2010

Sources:

9 – Hillmer AM, Hanneken S, Genetic variation in the human androgen receptor gene is the major determinant of common early-onset Androgenetic Alopecia (AGA). Department of Genomics, Life and Brain Center, University of Bonn, Bonn, Germany.
10 – Levy-Nissenbaum E, Bar-Natan M, Confirmation of the association between male pattern baldness and the androgen receptor genr Danek Gartner Institute of Human Genetics, Sheba Medical Center, Tel Hashomer, Israel
11- Hillmer AM, Flaquer A, Genome-wide scan and fine-mapping linkage study of AGA reveals a locus on chromosome 3q26. Department of Genomics, Life and Brain Center, University of Bonn, D-53127 Bonn, Germany.
12 – Petukhova L, Sousa EC Jr, Martinez-Mir A, Vitebsky A, Dos Santos LG, Shapiro L, Haynes C, Gordon D, Shimomura Y, Christiano AM. Genome-wide linkage analysis of an autosomal recessive hypotrichosis identifies a novel P2RY5 mutation. Genomics. 2008 Nov;92(5):273–8. Epub 2008 Sep 13. PubMed PMID: 18692127.






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