Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental conditions affecting young people. Studies suggest that about 1 in 20 young people have ADHD, but for every girl diagnosed, there are between three and seven boys who receive an ADHD diagnosis.

Dr Joanna Martin from the Wolfson Centre for Young People’s Mental Health has shared her expertise on the neurodevelopmental condition and why more research is needed to support young women who are diagnosed with ADHD.

The gender gap in diagnosis

Girls are less likely to be diagnosed with ADHD than boys. Recent research suggests that this gender gap can be partly explained by missed or delayed diagnosis of ADHD in girls. This may be due to adults (parents and teachers) not being aware of what ADHD looks like in girls or because of other factors and behaviours that girls may use to mask their symptoms of ADHD.

We need to learn more about what ADHD looks like in girls and how we can identify girls who need help with their ADHD sooner, so that they can benefit from health and educational resources and support.

Young people who are affected by ADHD have difficulties with things like sitting still, interrupting others, staying organised, and concentrating on school work. Some of the symptoms of ADHD may be more noticeable to other people (for example ‘being always on the go’) than other symptoms (for example ‘getting easily distracted’).

It has been suggested that ADHD symptoms in girls might sometimes be harder to notice than ADHD in boys. If ADHD is not diagnosed, a young person may struggle with their schoolwork and relationships, without knowing why and without receiving needed support. This can lead to mental health difficulties, such as anxiety or depression. As such, timely diagnosis is very important.

What causes ADHD?

One way to understand more about how ADHD differs in boys and girls is by looking at what causes ADHD.

We know from studies of families, including comparisons of identical and fraternal twins, that ADHD is largely genetic. A large international study from 2018 discovered some of the first genetic factors linked to ADHD. We now know that ADHD is a complex condition and thousands of different genetic risk factors collectively contribute to increasing the chance of having ADHD.

In a series of studies conducted by researchers at Cardiff University, in collaboration with a large international team of experts, we investigated genetic factors in boys and girls with ADHD. We used the world’s largest genetic dataset of people with and without ADHD (about 55,000 people) and looked at genetic factors which occur commonly in the population. We found no evidence of differences, meaning that the same genetic factors are important for ADHD in girls and boys.

This is important to know, but it does not explain why girls are less likely to have a diagnosis of ADHD. To examine this in another study, we focused on young people who had been diagnosed with anxiety and depression.

Anxiety and depression

Previous studies have suggested that genetic risk factors that are linked to ADHD, also play a role in anxiety and depression. In this study, we compared genetic risk factors related to ADHD in boys and girls who had these mental health conditions. We found that in the group of young people who had ever received a clinician’s diagnosis of any anxiety or depression, girls had a higher burden of genetic variants known to increase the risk for ADHD compared to boys.

These results indicate that genetic predisposition to ADHD may lead to different mental health problems in boys and girls and in particular, may lead to  being more likely to be clinically recognised and diagnosed as anxiety or depression in girls than in boys.

More recently, we followed up this work in a study of adults. We found only weak support for a gender difference in genetic factors linked to ADHD. Specifically, we found that women with depression were only more likely to have a higher genetic predisposition to ADHD than men if they had developed depression by young adulthood (that is by the age of 26) but not later. Together with the previous study, this indicates that ADHD genetic factors might be linked to early life anxiety and depression in young girls, but less so at later ages.

Supporting young people

We need more research to better understand the reasons for and impact of missed or delayed diagnosis of ADHD in young people. We also need to improve the early detection of difficulties. Early and accurate diagnosis of ADHD and mental health problems is necessary to make sure that all young people have the support they need.

Resources

• National Centre for Mental Health (NCMH)
• ADHD Foundation
• The Royal College of Psychiatrists

Dr Joanna Martin