Baldness and heredity: what is inherited and what is not

"My maternal grandfather was bald, so I will be too." "My father has all his hair, I am safe." Few health questions have as many popular certainties as the heredity of baldness. Science confirms that genetics weighs heavily, but the story is more complex than "it comes from the mother" or "it comes from the father".

In this article we explain what twin studies and large genetic studies show, where the myth of the maternal grandfather comes from, what is not inherited and what you can do with this information. Because inheriting the predisposition does not mean being condemned to it, and today it is possible to act early.

How much of baldness is genetic

The classic way to measure the weight of genetics is to compare identical twins (who share all their genes) with non-identical twins (who share about half). If identical twins resemble each other much more, genetics weighs heavily.

In an Australian study of male twins (Nyholt et al., 2003), the heritability of male baldness was estimated at about 80%. This means that, in the population studied, about 80% of the differences between men in baldness were explained by genetic differences. It is one of the highest values among common human traits, similar to that of height.

But 80% is not 100%

Even among identical twins there are differences. In a study of pairs of identical male twins (Gatherwright et al., 2013), the brother who smoked, had more stress, drank more or had more hours of sun exposure tended to have more hair loss in certain areas. Genetics provides the predisposition; the environment and habits modulate its expression.

And in women?

Female hair loss also has a hereditary component, with a family history in 40% to 54% of affected women, but the genetics are less studied and seem to be partly different from the male ones. See Female hair loss: what it is and how to recognise it.

The androgen receptor gene and the myth of the maternal grandfather

Where the myth comes from

DHT, the hormone that causes follicle miniaturisation, acts through the androgen receptor. The gene that codes for this receptor is on the X chromosome. Men have only one X chromosome, which they always inherit from their mother (from their father they inherit the Y). And the mother received that X from one of her parents, often her father, the maternal grandfather.

In 2005, Hillmer and colleagues showed that variants of this gene are an important risk factor for early-onset baldness. From this came the oversimplified idea that "baldness comes from the mother's side" and that all you need to do is look at your maternal grandfather.

Because it is only part of the truth

• A mother has two X chromosomes, one from her father and one from her mother, and passes one of them on at random. The maternal grandfather may be bald without the grandson inheriting the "at-risk" X.
• The receptor gene is not the only one. There are many other genetic regions on other chromosomes, inherited from both parents. Richards and colleagues (2008) identified a region on chromosome 20 which, combined with the risk variant of the androgen receptor, was associated with a risk about seven times higher.
• Fathers and sons look alike. Clinical observation and family studies show a relevant agreement between the degree of baldness of the father and that of the son, which would not be expected if everything came from the mother (Chumlea et al., 2004).

Conclusion: family history on both sides counts. Father, grandfathers, uncles and older brothers give clues about the risk, without any one of them determining it alone.

Hundreds of genes: what the large studies show

Over the past decade, studies of tens of thousands of men have compared the genome of those who have baldness with those who do not:

• Heilmann-Heimbach et al. (2017), in a European meta-analysis, identified 63 associated regions, which together explained about 39% of the variability in baldness.
• Pirastu et al. (2017), with more than 70,000 men, identified 71 regions.
• Hagenaars et al. (2017), with more than 52,000 men from the UK Biobank, found 287 genetic signals, many of them on the X chromosome.

What this means:

• Baldness is polygenic: it results from the sum of many variants, each with a small effect, and not from a single gene.
• Many of these genes are linked to follicle development, the response to androgens and the way hair grows.
• Even with hundreds of signals, individual prediction remains imperfect. The authors of the UK Biobank study themselves stressed that we are still far from an accurate prediction for each person, although it is possible to identify subgroups at much higher risk.

Some of these studies also found genetic links between baldness and other traits (such as height, age at puberty or bone density), which helps us to understand the biology, but has no practical application for the individual.

What is not inherited

Factors you can influence

• Smoking: associated with more hair loss, including in the twin study.
• Testosterone and anabolic steroids: they do not "create" baldness in those without a predisposition, but can greatly accelerate it in those who have one.
• Chronic stress, sleep and diet: they do not cause genetic baldness, but may add an effluvium that makes it more visible. See Stress and hair loss: what is known.
• Timing of treatment: starting early, while there are still many active follicles, makes a difference to the result.

Myths without basis

Genetic tests: are they worthwhile?

There are commercial tests that promise to calculate the risk of baldness or predict the response to treatments (for example, finasteride or minoxidil) from a saliva sample.

What is known:

• Individual prediction is limited. Even models based on hundreds of variants explain only part of the risk and cannot tell, with accuracy, whether or not a person will go bald, or when.
• Family history and clinical examination give comparable or better information, at no cost: a scalp examination with trichoscopy shows whether miniaturisation is already present, long before the loss is visible to the naked eye.
• "Treatment response" tests have limited validation and do not replace a supervised therapeutic trial.
• Privacy: genetic data is sensitive data. Before sending a sample, read how it will be stored and shared.

In short, today, a genetic test rarely changes the decision. The most useful thing is to know your family history and assess your scalp.

You have a family history. Now what?

Having relatives with baldness does not oblige you to do anything, but it lets you stay alert and act at the right moment:

• Know your family: father, grandfathers, uncles and brothers on both sides. At what age did they start? How far did it go?
• Track with photographs every three months, from the front, from the side (temples) and from above (crown). See Photos every 3 months: how to track the crown.
• Watch for the first signs: temples rising, crown opening up, thinner hairs, less volume. See Male pattern baldness: what it is and how to recognise it and Thinning crown: when it is worth assessing.
• Get assessed early if you notice changes, especially if you are under 30. Treatments are more effective at preserving than at recovering.
• Look after the modifiable factors: do not smoke, avoid anabolic steroids, sleep and eat well.

At Luxmed, the hair medicine consultation includes a detailed family history, examination, classification on the Norwood scale, trichoscopy and follow-up photographs. If miniaturisation is already present, we discuss the options with you, with benefits and risks. If not, you have a starting point to compare against in the future.

This article is for information purposes and does not replace a medical consultation. The results of any treatment vary from person to person.

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