Girls and ADHD: Why Are Boys Diagnosed More Often?

There are thirty kids in your child’s class, fifteen girls and fifteen boys. Of the fifteen boys, it seems like half of them have diagnosed ADHD, as opposed to only one of the girls. Why is this so? You may have heard that boys are more likely to have ADHD than girls. Alternatively, you may have heard that girls are just as likely to have ADHD but much less likely to be diagnosed because they don’t share the same “hyperactive” symptoms as boys. Which of these is true?

According to Russell Barkley, Clinical Professor of Psychiatry and Pediatrics at the Medical University of South Carolina, both are somewhat true…and at the same time, neither one is fully accurate.

 “It used to be that girls were less likely to be diagnosed with ADHD,” Barkley explains. “They weren’t making as much ‘trouble,’ so they didn’t get referred for a diagnosis.” Nowadays, however, the gap has closed. More and more girls are being referred and diagnosed with ADHD, and it’s harder for them to slip through the cracks.

At the same time, in some ways the quote is correct. Even though referral and diagnosis of ADHD in girls has improved tremendously, there still do seem to be more boys diagnosed with ADHD than girls, at least during childhood. Young boys are four times more likely to have ADHD than their female counterparts; adolescent boys are still more likely than adolescent girls to receive a diagnosis; but surprisingly, adult men and women seem to have about an equal chance of having ADHD.

Why is that? The answer is unclear. Dr. Barkley did describe one fascinating possibility that may explain the discrepancy between males and females when it comes to ADHD.

ADHD: A Sex-Linked Disorder?

As we all learned in high school biology, males are essentially missing part of a chromosome. Females have two full “X” sex chromosomes, whereas males have only one full “X” chromosome in addition to a stumpy “Y” chromosome. The Y chromosome, in evolutionary thought, is considered somewhat defective. “Biologically, females are the norm and males are the deviation from the norm,” explains Dr. Barkley.

This explains more than just ADHD. In fact, many childhood disorders – including autism and learning disorders – appear more in boys than in girls. That may be explained by the fact that many of these disorders are partially sex-linked, which means that the defective Y chromosome makes them more likely to appear in boys.

So how does that explain the fact that the gap between males and females closes as we reach adulthood? According to Dr. Barkley, it could be that the genes for the phenotype of ADHD – its external symptoms – are sex-linked, even if other ADHD-related genes are not. “It’s important to understand that ADHD, like any of these disorders, is not just dependent on a single set of genes,” explains Dr. Barkley. If the genes that actually allow the ADHD to be expressed are on the Y chromosome, it may cause them to be expressed more quickly if they were on an X chromosome.