How is “hairiness” encoded in your DNA?
An investigative report on how researchers zeroed in on the genetic underpinnings of “excessive hairiness” in females
Why do some women have more body hair than others? Find out more below.
Highlights
- Learn how a specific sex hormone (more common in men) can play a major role in female excessive hairiness.
- Find out how scientists figured out the genetic link to excessive hairiness in women.
- Discover an easy way to learn whether you are genetically predisposed to excessive hairiness.
Adaptation and Hair Type
Hair type is one of the most differentiated traits among human populations.
African populations tend to have “frizzier” hair than people in Europe or Asia. Asian hair tends to have a thicker and more circular cross-section than African and European hair.
And there’s a simple reason for this: adaptation. As Homo sapiens adapted to new and diverse environments, several phenotypic differences developed — including hair type.
The particular genes that have played a part in shaping hairiness (a very complex trait) have only recently been identified.
Hirsutism = hairiness
Excessive hairiness for females is medically termed hirsutism. This refers to women with excessive growth of male-pattern terminal hair (“terminal hair” refers to the dark, thick hair that covers the body).
5–15% of most populations have hirsutism, with slightly lower frequency in East Asian populations. In most cases, the cause of hirsutism is abnormal circulating levels of the male hormone androgen.
5–15% of most populations have hirsutism, with slightly lower frequency in East Asian populations.
Androgen is produced in both male and female bodies and plays an important role for the development of male traits and reproductive function.
However, the contribution of androgen to hairiness depends on hair type and localization. For example, sexual hair localized in the pubic area and armpit, and terminal hair on the lower arms and legs are sensitive to low levels of androgen. On the other hand, sexual hair localized on the face, back and upper arms are only sensitive to high levels of androgen.
The Genomic Basis for Excessive Hairiness
By now you may be wondering: All this talk about androgen is interesting, but what does that have to do with DNA?
Here’s where recent research from Japan can help.
The researchers performed GWAS (genome-wide association study) using the genomic data of 11,311 Japanese women who answered survey questions on skin-related phenotypes.
Previous hair-density trait analyses suggested that excessive hairiness shares genetic signals with eyebrow thickness. This recent study identified new loci (think of loci like a genetic “street address”) for excessive hairiness in TBX15 (rs984225), BCL2 (rs7226979), GCC2 and LIMS1 (rs6542772).
Before this recent paper, TBX15 was linked to hair pigmentation and hair length in mice, as well as muscle fiber type and metabolic subtypes of fat cells called adipocytes. In a trans-ethnic meta-analysis of European and African-American populations, one of the top variants (rs984222) in the TBX15 gene was associated with BMI and waist-hip ratio.
However, this Japanese study turned up some surprising results. For one, the researchers employed a different set of analytical tools in the current study and found a negative association with BMI and hip circumference. Their results suggest excessive hairiness is not related to being overweight or obese.
Taken together, the Japanese researchers proposed that genetic variants in TBX15 influence a number of traits including skeletal development, fat store distribution, and hair follicle density and/or activity.
This study identified new loci in TBX15 (rs984225), BCL2 (rs7226979), GCC2 and LIMS1 (rs6542772) for excessive hairiness.
BCL2 is a type of protein that blocks cell death and regulates the life and death cycle of hair follicle growth. Since regulation of the cycle is a crucial process of hair growth, the researchers suggested that differences in BCL2 expression may shift the timing or length of the hair follicle life cycle and thereby lead to variation in hair-density between individuals.
Finally, the results of this study suggest that SNPs (specific gene variations, pronounced “snips”) may impact the expression of both the GCC2 and LIMS1 genes.
Genome-wide association study in Japanese females identifies fifteen novel skin- related trait associations.
Are you genetically predisposed to excessive hairiness?
It’s possible to use research like this Japanese study to find out if you are genetically predisposed to excessive hairiness.
Recently, leading DNA analysis company Genomelink did exactly this, using this new paper to algorithmically test for excessive hairiness.
So if you’re interested in finding out whether you’re genetically predisposed to hirsutism and already have a DNA test result, then click HERE to get started within minutes.
Once you’ve completed your sign up, you’ll start receiving your first free traits (over 100 free in all) and get access to all of Genomelink’s ancestry and wellness reports, a personalized avatar, and much more.
Check out your genetic predisposition for Excessive Hairiness on Genomelink
Appendix
The Modified FG score
0 (no hair) ~ 4 (equivalent to a hairy man)
Determining hirsutism is difficult. In 1981, Hatch and colleagues proposed that women with mFG score ≧ 8 have hirsutism.
