What are the chances of my children inheriting my baldness?
A curious adult from Canada asks:
"My father has a common baldness problem. I am having it too. What are the chances of my kids having the same problem?"
Tough question to answer! The genetics of male pattern baldness (MPB) aren’t that well understood. Which means it is hard to predict whether or not you'll pass your MPB on to your sons.
One of the things that makes MPB so hard to figure out is that it is so common. Around 85% of men are reported to have thinning hair by the age of 50. It is almost like we should be studying why some men don't go bald!
If you aren't careful with these kinds of numbers, you can run into all sorts of problems. Imagine a study that looks at 50-year-old men and their 90-year-old fathers.
You'd have half the dads with sons who were balding just by random chance. So you might conclude that dads pass their balding patterns on to their sons.
But you might be wrong. Because balding is so common, it is the timing that matters not whether or not you are balding.
Genetics of baldness
So what does the latest research show? The most recent work suggests that a big part of men's MPB comes from mom's side of the family and not dad's.
You may have heard that you can tell whether or not you'll go bald by looking at the men on your mom's side of the family. This is based on a study done in 1916!1 In 2005, a German group used modern genetic approaches to show that the conclusion of this study is at least partly true.2
The German group looked at the DNA of 391 people including 201 men that were balding. These folks were from 95 separate families.
The researchers then compared the DNA of balding people with people not balding and looked for differences. What they found was that balding folks more often had certain differences on their X chromosome.
As you'll probably remember, the X is one of the human sex chromosomes. If you have two X's, then you develop as a female. An X and a Y means that you are male.
Men only get their X chromosome from their mothers. Fathers give their sons the Y that makes them male and mothers give them the X, which contains 1200 or so genes needed to survive.
So the DNA changes that make MPB happen earlier come from mom and her X chromosome. Where exactly on the X chromosome are the DNA changes that lead to MPB? They are all in the androgen receptor (AR) gene.
Many of the characteristics associated with being a male happen because of the interaction of testosterone (and its derivatives) with the AR protein. AR turns genes on or off when testosterone is around.
The fact that AR is involved in MPB makes sense in a lot of ways. Men with male pattern baldness tend to have different levels of testosterone.3 Also, one of the treatments for male pattern baldness is something called Propecia.
Propecia works by changing the amount and potency of testosterone. In other words, Propecia changes how a balding man's AR gene works.
Easy as pie. Men get their X chromosome from mom and certain DNA changes on the X chromosome lead to early onset MPB. If only it were this easy!
Other causes of baldness
These changes are not enough by themselves to lead to baldness. We know this because there were men in the study who had these DNA changes but were not going bald. And vice versa.
What is going on is that there is probably more than one gene involved in male pattern baldness. And these other genes can come from mom and/or dad.
So an important part of balding comes from mom's side of the family because of the AR gene. These changes are not enough, though. Other unknown genes may affect whether or not DNA changes in the AR gene will cause baldness. And there may even be some sort of trigger needed from the environment.
This is why it is hard to predict whether or not you will pass your balding on to your son. What does his grandpa on his mom's side look like? If he has a full head of hair, then maybe the odds are less for your sons. Maybe.
Author: Dr. D. Barry Starr
Barry served as The Tech Geneticist from 2002-2018. He founded Ask-a-Geneticist, answered thousands of questions submitted by people from all around the world, and oversaw and edited all articles published during his tenure. AAG is part of the Stanford at The Tech program, which brings Stanford scientists to The Tech to answer questions for this site, as well as to run science activities with visitors at The Tech Interactive in downtown San Jose.