Male pattern baldness, or androgenetic alopecia, is a well known condition in men that starts with a receding front hairline or a bald spot on the top of the head. The word androgenetic refers to androgens, or male sex hormones (predominantly testosterone) and alopecia is the medical term for hair loss.
What most people don't realize is that this condition can also affect women, in whom it is called female pattern baldness. Fortunately, it rarely causes complete baldness in women, but it does cause generalized thinning and can be quite distressing.
Let's take a look at the causes of this condition and how you can assess your risk of hair loss.
Testosterone is a factor in all cases of androgenetic alopecia. Generally, higher levels of testosterone are associated with more rapid loss of scalp hair, as well as increased facial and body hair. Women also have testosterone, and these effects of higher levels occur in them, too (although female pattern baldness does not necessarily mean that a woman has high testosterone levels).
Androgenetic alopecia also has a strong genetic predisposition, so your family history is an important part of determining your risk. Changes in several genes contribute to hair loss, but abnormalities in the androgen receptor (AR) gene - located on the X chromosome - are among the most significant genetic cause of this type of baldness.
Women have two X chromosomes, whereas men have one X and one Y chromosome. Men always get their Y chromosome from their fathers and their X chromosome (where the AR gene is located) from their mothers. Therefore, since the X chromosome (and the AR gene) figures prominently in most cases of androgenetic alopecia, a family history of hair loss in a man's mother and maternal grandparents (the side of the family that supplies his X chromosome) is more important than a similar history on his father's side.
But, since other genes can also causes baldness, men can still inherit male pattern baldness through their fathers. Women get one X chromosome from each parent, so both sides of the family history are equally important for them.
Recently, a genetic test that looks for changes in the AR gene became available for determining a person's predisposition to androgenetic alopecia. Although there are other causes of hair loss, if you are already experiencing this symptom, an abnormal result on this test can increase confidence in a diagnosis of androgenetic alopecia. However, even in those individuals, it is still worth looking for (and treating) any other identifiable causes.
There is good evidence that medical treatments are better at preserving existing hair than they are at regrowing new hair. So if you are worried about hair loss, or have a family history of it, an abnormal result in the AR gene test could alert you to your greater than average risk and allow you to begin treatment as soon as possible, hopefully avoiding or minimizing hair loss. The problem with this approach, though, is that not everyone with an abnormal test result will go on to develop androgenetic alopecia, so some people may needlessly worry or purchase and use expensive treatments that do them no good.
Another possible benefit of this AR gene test is that a normal result could reassure people with a lower risk of baldness. Remember, though, that there are other genetic factors to consider when thinking about hair loss, plus several environmental factors that we haven't even discussed yet. So a normal androgen receptor test doesn't guarantee a full head of hair!
A lot of controversy surrounds these types of predictive genetic tests. One of the main concerns is the risk that people will incorrectly believe that the results are "black or white" and translate into a definite clinical outcome - in this case, that they will either develop male or female pattern baldness or be totally free of it.
I don't see a large role for this particular test right now, but some people may feel strongly that they want to know this information. For those individuals, I stress the importance of understanding that hair growth represents a complex interplay of multiple environmental and genetic factors, and that no single test can completely predict one's future.