'Late-Onset' ADHD Appears In Adulthood: Study

Even though childhood attention-deficit/hyperactivity disorder (ADHD) can also be experienced by adults, a new study by King's College London shows that the disorder can emerge after childhood too in some people.

This developmental disorder can lead to inattention, hyperactivity, and impulsivity, which is a common behavioral disorder among children. It was believed until now that those who underwent the disorder into adulthood experienced adult ADHD.

In a new study, however, scientists found that almost 70 percent of young adults with ADHD did not seem to reveal the disorder in their childhood. The findings thus show that is possible to have "late-onset" ADHD while patients in the study showed high levels of symptoms, impairment, and other mental health disorders.

"We were very interested in this large 'late-onset' ADHD group, as ADHD is generally seen as a childhood-onset neurodevelopmental disorder," said Jessica Agnew-Blais of King's College London and first author of the study. "We speculated about the nature of late-onset ADHD: the disorder could have been masked in childhood due to protective factors, such as a supportive family environment. Or it could be entirely explained by other mental health problems."

"Alternatively, late-onset ADHD could be a distinct disorder altogether," she added. "We think it is important that we continue to investigate the underlying causes of late-onset ADHD."

More than 2,200 British twins from the Environmental Risk (E-Risk) Longitudinal Twin Study were examined. They had been assessed for childhood ADHD through mother and teacher reports at the ages of 5, 7, 10 and 12.

By examining twins, researchers got an insight into the genetic basis of ADHD, showing that adult ADHD is less heritable than childhood ADHD. Moreover, having a twin with childhood ADHD did not seem to impact the development of late-onset ADHD.

"Our research sheds new light on the development and onset of ADHD, but it also brings up many questions about ADHD that arises after childhood," said Louise Arseneault, also of King's College London and senior author of the study. "How similar or different is 'late-onset' ADHD compared with ADHD that begins in childhood? How and why does late-onset ADHD arise? What treatments are most effective for late-onset ADHD? These are the questions we should now be seeking to answer."

The findings were published in the May 18 issue of JAMA Psychiatry.