The genetics of baldness: More complex than you might think
From bald eagles to Bruce Willis, bald spots are a common sight and part of the fabric of our society. It’s often assumed that baldness has a genetic component to it, and that’s absolutely true; it does. But it’s also commonly believed that baldness is inherited from your maternal grandfather. That part isn’t entirely true. As with many concepts in genetics, there’s a lot more to it than that!
Both men and women experience hair loss, but research has historically focused primarily on male subjects (and efforts to link the two have shown that female pattern hair loss is not predicted by the same genetic markers). Because of this, significantly less is known about female hair loss. We do know that approximately 30% of males experience some degree of hair loss (including simple hair thinning or a receding hairline) by the age of 30, 50% by the age of 50, and 80% by the age of 701.
Male pattern baldness (MPB) is a condition where hair loss occurs in multiple parts of the scalp, ultimately leading to a bald region surrounded by hair in a horseshoe-like pattern3.The process of going bald is more complex than simply hair falling out, though. For starters, individuals with MPB are known to have smaller hair follicles on their scalp. Hair follicles are made of multiple cell types, each one dedicated to a particular process in building hair, which is actually a long chain of proteins (mostly keratin, which you can read about here) outside those cells. These follicles are where hair gains its unique features like curliness and color. Individuals with MPB not only have smaller follicles, but those follicles produce less hair, which contributes to the hair thinning process. Eventually, these follicles die, which produces a bald spot1-4.
But why do some people go bald while others don’t?
Large scale genetic studies have shown that DNA plays a big part in determining whether MPB will develop2-4. A common saying is that hair loss can be traced back to a person’s grandfather on their mother’s side. While this isn’t entirely true, there is some genetic evidence behind it. One of the well-known genes related to hair loss is the AR gene which codes for the androgen receptor protein. Among other functions, this protein helps hair follicle cells detect androgen hormones (like testosterone) that circulate through the body. Testosterone and other androgens can affect when, where, and how much a person’s hair grows1. The AR gene is located on the X chromosome, which means that, for males, it was inherited from their mother. While this seems to lend credence to the notion that baldness is inherited from a person’s maternal grandfather, research indicates that the story is more complex than that. Recent studies report that MPB is a polygenic condition, meaning there are many genetic variants involved2. In fact, many of the genetic variants associated with MPB are not located on sex chromosomes. When considered together, these variants have been found to be more predictive of MPB development than variants that are located on sex chromosomes2.
Although scientists have found DNA variants that seem to predict the likelihood of MPB development, it’s not entirely clear how these minor changes in the DNA lead to hair loss. Many of these variants are located in or near genes involved in the process of forming and maintaining hair follicle cells, indicating that these changes somehow affect the biology of hair follicles. Lots of proteins are involved in making and maintaining hair follicles, and we need to take all of them into account if we want to find the most complete answer1.
DNA cannot be used to predict everything about a person’s future, but it can be used to make useful estimates of how likely it is that a person will have certain physical traits. MPB is a good example of this. Scientists can determine how many MPB associated DNA variants a person has, and use them to estimate their likelihood of experiencing hair loss. Individually, each gene may be associated with slightly higher odds of going bald; however, a person’s chances increase with each additional variant they inherit. Some people inherit a specific combination of variants that increases their likelihood of developing MPB by 58%2. This kind of analysis—where multiple genetic variants are taken into consideration—is common in genetics and helps strengthen the predictive ability of some types of genetic tests.
So, what’s the bald truth on baldness? MPB can be inherited from either side of a person’s family, and there are ways you can learn more through a DNA test. In the Helix Store, HumanCode’s BABYglimpse and DNAPassport can give you insights into your predisposition for male pattern baldness. And if the evidence comes back strong, who knows? You might just be the next Samuel L. Jackson.
2Hagenaars, Saskia P. et al. “Genetic Prediction of Male Pattern Baldness.” Ed. Markus M. Noethen. PLoS Genetics 13.2 (2017): e1006594. PMC. Web. 11 Dec. 2017.
3Heilmann-Heimbach, Stefanie et al. “Meta-Analysis Identifies Novel Risk Loci and Yields Systematic Insights into the Biology of Male-Pattern Baldness.” Nature Communications 8 (2017): 14694. PMC. Web. 11 Dec. 2017.
4Pirastu, Nicola et al. “GWAS for Male-Pattern Baldness Identifies 71 Susceptibility Loci Explaining 38% of the Risk.” Nature Communications 8 (2017): 1584. PMC. Web. 11 Dec. 2017.