The delayed brain development long associated with ADHD may simply be a gender difference.
The exact cause of attention-deficit hyperactivity disorder (ADHD) in children is not clearly understood. One of the main hypotheses is that it is caused by delayed maturation of the cerebral cortex, but research findings have been published that challenge this theory.
Attention problems and cortical maturation in a large longitudinal sample of youths: The importance of accounting for sex differences | PNAS
Case of mistaken patterns: Slow brain development linked to ADHD for years might just be sex differences
https://medicalxpress.com/news/2026-05-case-mistaken-patterns-brain-linked.html
A study published by Shannon D. O'Connor and colleagues at the University of Vermont suggests that 'previous research linking ADHD to the cerebral cortex may have misinterpreted normal developmental differences between boys and girls as developmental delays associated with ADHD.'
A well-known study linking ADHD to the cerebral cortex is the 2007 work by Philip Shaw et al . Shaw and his team surveyed 223 children with ADHD and showed that brain regions involved in attention, decision-making, and self-control appeared to mature several years later in children with ADHD than in their peers without ADHD. This study has shaped scientists' understanding of ADHD for many years since.
Since this study, brain imaging technology has advanced dramatically, allowing scientists to observe the brain with greater clarity and detail than ever before. With access to these advanced technologies, O'Connor and his colleagues decided to re-examine the link between ADHD and brain development using an even larger sample size.
The research team examined a total of 26,496 brain images collected from 5,782 boys and 5,311 girls through the publicly available Adolescent Brain Cognitive Development study. They also used the Child Behavior Checklist, a questionnaire in which parents assessed their children's attention-related problems.
Subsequently, the researchers used MRI images to measure the thickness of the outermost layer of the brain, called the cerebral cortex, and tracked the natural thinning of the cortex as children grew. They then input this data into a computer model to examine the relationship between attention scores and the rate at which the cortex thinned.
The results showed that boys' brains naturally thin more slowly than girls'. Since boys are generally more likely to be diagnosed with ADHD, previous studies may have misinterpreted the slower rate of cortical thinning as a sign of ADHD itself. When biological differences between boys and girls are properly taken into account, the previously thought to be a link between attention problems and brain development completely disappears.
Furthermore, when O'Connor and his colleagues analyzed brain images of children with a high genetic risk of ADHD, they found that in some children, the rate of cortical thinning was actually faster.
Based on these results, O'Connor et al. pointed out that 'unless differences in brain development between boys and girls are carefully considered, patterns of cerebral cortex maturation should not be used as an indicator of attentional impairment.'
Another study published by Sonya LaBianca and colleagues at the University of Copenhagen shows that the number of cases is increasing despite a decreased genetic risk of ADHD or autism spectrum disorder (ASD) compared to the past.
Changes in Genetic Contributions to ASD and ADHD by Year of Diagnosis | Attention Deficit/Hyperactivity Disorders | JAMA Psychiatry | JAMA Network
https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2850079
People diagnosed with ADHD and autism more recently show lower genetic risk than earlier cases
https://medicalxpress.com/news/2026-06-people-adhd-autism-genetic-earlier.html
LaBianca and colleagues analyzed more than 37,000 Danes diagnosed with ASD or ADHD between 1994 and 2016 and found that the genetic risk for ASD and ADHD decreased over time. While people currently diagnosed with ASD or ADHD have a higher genetic risk than the general population, it is not as pronounced as in patients diagnosed 20 years ago.
Nevertheless, the number of people diagnosed with ASD or ADHD has increased four to ten times compared to before. This is thought to be because the criteria for the two disorders have been expanded and they are now recognized as lifelong disabilities rather than childhood disorders, meaning that more people are now considered to fit the description.
LaBianca et al. wrote, 'We support the view that the expansion of diagnostic criteria is a factor in the increase in the diagnosis rate. We still need to understand if there are underlying biological risk factors.'
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