Science of Male Pattern Baldness

The medical term for male pattern baldness is androgenetic alopecia (AGA). It is genetically determined, progressive hair loss and is the most common form of hair loss in men, and diffuse hair thinning in women. It affects 30% of men under the age of 30, 50% of men by age 50, 66% of men age 60, and 80% of men over the age of 70. AGA affects an estimated 50 million men and 30 million women in the U.S.

AGA commonly begins in the mid-twenties and early thirties. The hair loss is progressive and occurs in a particularly recognizable pattern beginning with a receding hairline at the temples and diffuse hair thinning.  Hair loss increases and progresses over the years to hair loss at the vertex, or crown. The time to baldness has been reported as 15-25 years, but some men go bald in less than five years.

Who is at risk for AGA?

Caucasian men are more frequently affected and their AGA is more severe than other ethnicities. Japanese men have been found to suffer AGA beginning a decade later than white men. Blacks, Native Americans and African American men are more likely to have late onset baldness. MPB occurs less often in Asian men.

What causes AGA?

Studies report that 80% of MPB is caused by a combination of genetics, and hormones. Specifically, androgens or male sex hormones are the most common cause of AGA in genetically susceptible men. Even normal levels of these hormones can cause hair loss in men with genetic susceptibility.

What causes hair loss in AGA?

AGA alters hair cycle development. Each hair follicle, which normally grows hair for 2-6 years, does so in a cycle from growth to resting phase to regeneration. The growth phase (called “anagen”) lasts 2-6 years. During the growth phase a new hair is formed, and as it grows it pushes the old hair out. The resting phase occurs every 3 months. After the resting phase, the hair is shed, and the next growth cycle begins.

In MPB, men who are genetically predisposed to hair loss, have an enzyme called 5-alpha reductase that turns testosterone into dihydrotestosterone (DHT). DHT attaches to the hair follicles causing them to shrink with every growth cycle.

Over time, the hair follicles become smaller and grow only shorter, finer hair. This is called hair follicle miniaturization which is a hallmark of male pattern hair baldness.  Finally, the follicle wears out and will no longer grow hair. The hair loss is permanent and irreversible. But, when the follicle wears out and will no longer grow hair, the hair loss is irreversible.

Note that this condition is potentially partially reversible, even at this late stage. IS THIS TRUE?

In addition, new studies report the importance of microscopic inflammation of the hair follicles related to another hormone called Prostaglandin D2. Prostaglandin D2 causes hair follicles to stop working, which prevents hair growth.

The genetics of AGA

  • AGA ha a known polygenetic mode of inheritance, meaning AGA is inherited when multiple genes are involved.
  • The gene for baldness is found on the X chromosome inherited by men from their mothers. But, that is not the whole story. Men with bald fathers have an increased risk of going bald as compared to men whose fathers have a full head of hair. Recent research in the genetics of MPB have identified additional genes that may contribute to susceptibility of MPB.
  • Genetic testing is focused on the androgen receptor gene (the “AR gene”) found on the X chromosome. The AR gene causes alterations in the hair growth cycle due to the hormone DHT. A positive test result for the AR gene indicates a 70% chance of MPB.
  • Other research suggests that the tiny muscles that surround and nourish the hair follicles lose their attachment to the follicles causing some of the first signs of MPB, thinning hair. This is an important discovery because it suggests that early treatment may halt or delay the loss of hair follicles.
  • The involvement of environmental and other nongenetic factors has only recently been studied. Climate, lifestyle, and socioeconomic factors related to geographical area play an important role. Additionally, Body Mass Index may play a role, and we know that heart disease, insulin resistance, hypertension, high cholesterol, and obesity are linked to AGA.

Risk factors associated with MPB

  • MPB increases the risk of heart attack, hypertension and high cholesterol.
  • MPB increases the risk of both melanoma and non-melanoma skin cancers.
  • MPB has been positively associated with an increased risk of benign prostatic hyperplasia (BPH) and prostate cancer.

These risk factors are modifiable in some cases, by adopting a healthy life style including controlling blood pressure, exercise and diet to support heart health.


References:

  • Sinclair, Rodney, Niloufar Torkamani, and Leslie Jones. “Androgenetic Alopecia: New Insights into the Pathogenesis and Mechanism of Hair Loss.” F1000Research 4.F1000 Faculty Rev (2015): 585. PMC. Web. 27 June 2018.
  • Cranwell W, Sinclair R. Male Androgenetic Alopecia. [Updated 2016 Feb 29]. In: De Groot LJ, Chrousos G, Dungan K, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK278957/
  • https://medlineplus.gov/ency/article/001177.htm
  • Hagenaars SP, Hill WD, Harris SE, Ritchie SJ, Davies G, Liewald DC, et al. (2017) Genetic prediction of male pattern baldness. PLoS Genet 13(2): e1006594. https://doi.org/10.1371/journal.pgen.1006594
  • Yamada T, Hara K, Umematsu H, et al
  • Male pattern baldness and its association with coronary heart disease: a meta-analysis
  • BMJ Open 2013;3:e002537. doi: 10.1136/bmjopen-2012-002537
  • Avital, Yaniv Shalom et al. “Study of the International Epidemiology of Androgenetic Alopecia in Young Caucasian Men Using Photographs From the Internet.” Indian Journal of Dermatology 60.4 (2015): 419. PMC. Web. 27 June 2018.

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