While attention-deficit hyperactivity disorder (ADHD) is often detected during childhood and continues into adulthood, new research suggests that for some people, the disorder emerges until much later, leading to misdiagnosis.

Late Onset Of ADHD

In a new study, a team of experts from King's College London examined records from 2,200 twins in Britain.

In order to assess signs of childhood ADHD, researchers collected mothers' and teachers' reports on children aged 5, 7, 10 and 12.

To determine adult ADHD, they conducted private interviews with study participants at age 18 and applied a special method for symptoms of inattention.

Additionally, because the research was a cohort of twins, scientists analyzed the potential genetic basis of ADHD.

Researchers discovered the following:
- About 70 percent of those with ADHD as young adults did not meet the criteria for the disorder in any childhood assessments. Therefore, they were not diagnosed when they were kids.
- These patients with "late onset" of ADHD had higher levels of symptoms, impairment, and other mental health disorders compared to others.
- Adult ADHD was less hereditary than childhood ADHD.
- Having a twin with ADHD did not place a person with higher risk of developing late-onset ADHD.

Another study from Brazil corroborates with the British report, revealing that a large percentage of adults with ADHD were not diagnosed during childhood.

Implications Of The Research

Both studies shed light on the development and onset of ADHD, and bring to the table unanswered questions about ADHD when it appears during childhood.

Louise Arseneault, lead author of the King's College study, said they want to know how similar or different late-onset ADHD is compared to the better-known ones, how and why late-onset ADHD arises, and what the most effective treatments are for this version of the disorder.

Dr. Jessica Agnew-Blais, a co-author of the study, said they proposed three possible explanations.

First, late-onset ADHD could have been masked during childhood due to factors such as high intelligence or a supportive family environment.

Second, patients diagnosed with late-onset ADHD may not have the disorder but another one with similar symptoms, such as anxiety. This in particular could lead to misdiagnosis and mistreatment.

Third, late-onset ADHD may be a distinct disorder altogether, said Agnew-Blais.

"We think it is important that we continue to investigate the underlying causes of late-onset ADHD," she added.

The details of the study are published in the journal JAMA Psychiatry.

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