Male-pattern baldness tendency

A region on the X chromosome, near the genes that respond to male hormones, is the single strongest genetic signal for male-pattern baldness. Baldness is roughly 80% heritable and shaped by many genes, so this one marker captures only part of the picture.

What this variant marks

This variant sits on the X chromosome, in the region containing the androgen receptor gene and its neighbour EDA2R. Male pattern baldness is driven by hair follicles on the scalp becoming sensitive to dihydrotestosterone, which shortens their growth phase until the follicle miniaturises, and the androgen receptor is the mechanism through which that happens.

The X-linked region is the single strongest genetic signal for the trait, which is why it is the one read here.

How strong the evidence is

In a study of 3,891 men with androgenetic alopecia and 8,915 controls, this variant was associated at an odds ratio of about 2.2 per copy with a p-value below 1e-90, which is a large effect for a common variant and is supported by three publications in this site's evidence file.

It is also only part of the picture. Later studies have identified hundreds of loci across the genome for male pattern baldness, and polygenic scores built from them predict severe early baldness far better than any single variant does.

Where the mother's-father folklore comes from

The old claim that baldness comes from your mother's father is a distorted version of something true. Men inherit their single X chromosome from their mother, so an X-linked baldness variant reaches a man through his mother, and her father is a visible place to look for it.

But the strongest locus being X-linked does not make the trait X-linked. Many autosomal variants contribute too, which is why baldness clearly tracks through fathers as well. Looking at both sides of the family remains a better predictor than either the folklore or this single variant.

What this variant does not tell you

It cannot tell you when hair loss would start, how far it would progress, or whether treatment would help. The pattern and rate vary enormously among men with the same genotype.

It also says nothing about the other causes of hair loss, including thyroid disease, iron deficiency, telogen effluvium after illness or stress, and alopecia areata, which is autoimmune and behaves completely differently. Sudden or patchy loss is a reason to see a doctor rather than to consult a genotype.

What each rs2497938 genotype means

rs2497938 has three possible genotypes: TT, CT and CC.

Higher baldness tendency (rs2497938 TT). On the strongest single baldness marker you carry the higher-risk version (one copy if you're male, since this is on the X chromosome; two copies if you're female). On its own this nudges the odds of male-pattern hair thinning upward, but baldness is shaped by many genes plus age and hormones, so it's a tendency, not a guarantee.

Mixed / intermediate tendency (rs2497938 CT). You carry one higher-risk and one lower-risk copy of this baldness marker (this mixed result only occurs in females, who have two X chromosomes). It places you in between for this single gene, and your overall hair outcome depends on many other genes and on hormones and age.

Lower baldness tendency (this marker) (rs2497938 CC). On this strongest single baldness marker you carry the lower-risk version (one copy if you're male, two if you're female). That's a favorable sign, but male-pattern baldness is about 80% heritable and driven by many genes, so this one marker can't rule it out and plenty of people with this result still thin over time.

Evidence & sources

This variant appears in 3 published genetic studies: PubMed 22032556 · PubMed 22693459 · PubMed 28196072.

Common questions

Will I go bald? This variant shifts the odds by about twofold per copy, and hundreds of other variants contribute. It cannot tell you whether, when or how far. Family history on both sides remains more informative than this single result.

Is baldness really inherited from the mother's side? Partly. The strongest known locus is on the X chromosome, which men inherit from their mothers, so that side carries the largest single signal. But many other contributing variants are autosomal and come from either parent.

Related

Body mass index · Eye color (blue, green/hazel, brown) · Freckling / sun sensitivity · Hair thickness / shovel-shaped incisors · Height · Muscle fiber type (power vs endurance) · Red hair / fair skin (MC1R gene)