Genetics of androgenetic alopecia: Is it true that it is inherited from the maternal grandfather?

Genetics of androgenetic alopecia: is it really inherited from the maternal grandfather?

There is a widespread belief in folk medicine that says: "If you want to know if you are going to go bald, look at your maternal grandfather."

This idea, known as the maternal grandfather rule , has a partial scientific basis, but does not fully explain the complex genetics of androgenetic alopecia , in both men and women.

Let's analyze this in detail:

• Which genes are involved in baldness?

• What role does the X chromosome play?

• Why do some men go bald even though their grandfather wasn't bald?

• How can you estimate the actual risk of hair loss?

  
  

What is androgenetic alopecia?

Androgenetic alopecia is the most common cause of hair loss in men and women. It is mediated by the action of androgenic hormones (primarily dihydrotestosterone or DHT) on genetically predisposed follicles, causing their progressive miniaturization.

But the key factor is not just hormonal: it's genetic .

The role of the AR gene and the X chromosome

One of the most important genes in the genetics of androgenetic alopecia is the AR gene , which encodes the androgen receptor. This gene is located on the X chromosome , specifically at the Xq11–Xq12 locus.

This explains why:

• Men are more vulnerable to baldness.

• Maternal inheritance has a significant impact.

• The maternal grandfather may be a partial predictor of risk.

  
  

Men have only one X chromosome, inherited exclusively from their mother. If that chromosome contains a variant of the AR gene that is particularly sensitive to male hormones, the risk of hair loss increases significantly.

So… why don't all the grandsons of bald men go bald?

Because androgenetic alopecia does not depend on a single gene .

Today we know that it is a polygenic disease, that is, influenced by multiple genes distributed across different chromosomes, not just the X chromosome.

Large-scale genomic studies, such as those conducted at the UK Biobank, have identified more than 300 genetic variants associated with the risk of baldness.

Key autosomal genes in baldness

In addition to the AR gene, important regions have been identified in:

• Chromosome 20 (20p11) → one of the most relevant

• Chromosome 2

• Chromosome 7

• Others.

These genes can be inherited from both the father and the mother and act as risk modulators , adding to the effect of the X chromosome.

How androgenetic alopecia inheritance really works

In practical terms, the risk of baldness works like a cumulative system:

Genetic factor	Approximate impact
Bald maternal grandfather (mutated AR gene)	High risk
Variant of chromosome 20	Moderate-high risk
Other secondary genes	Additional risk

It is possible not to inherit the altered AR gene from the X chromosome, but if enough variants accumulate on other chromosomes, androgenetic alopecia can also develop.

What role does the father play in baldness?

Although traditionally ignored, the father also has a significant influence. Not through the X chromosome, but through the autosomal genes he passes on to his children.

Studies show that:

• Non-bald father + non-bald maternal grandfather → low risk

• Bald father + non-bald maternal grandfather → risk x2.5

• Bald maternal grandfather + non-bald father → moderate-high risk

• Bald father + bald maternal grandfather → very high and early risk

  
  

Is there a reliable genetic test to find out if I will go bald?

Currently, there is no clinically useful genetic test to accurately predict androgenetic alopecia, due to:

• The large number of genes involved

• The interaction between hormonal, environmental, and epigenetic factors

• Individual variability in gene expression

  
  

Current commercial tests do not offer reliable predictions for clinical practice.

Can the severity or age of onset be predicted?

With some approximation, yes:

• Maternal inheritance is often associated with an earlier onset

• Paternal inheritance may be associated with slower progression

• The combination of both usually leads to more intense forms

  
  

However, there are no absolute rules.

Medical conclusion

The genetics of androgenetic alopecia are complex, polygenic, and multifactorial. Although the X chromosome and the AR gene explain part of the risk, autosomal genes inherited from both the father and the mother are equally important.

The famous “maternal grandfather rule” is not false, but it is incomplete.

True clinical prediction continues to be based on:

• Combined family history

• Dermatological examination

• Individual evolution