Although current research suggests that childhood attention-deficit/hyperactivity disorder (ADHD) can continue into adulthood, a new study by King's College London researchers suggests that it is also possible for the disorder to emerge after childhood in some people.
ADHD is a developmental disorder that causes inattention, hyperactivity and impulsivity. It is one of the most common behavioral disorders in children, and until now, it was widely believed that those experiencing the disorder into adulthood possessed adult ADHD.
The new study throws this hypothesis on its head, revealing that nearly 70 percent of young adults with ADHD in the study did not meet the criteria for the disorder during any of their childhood assessments. The findings suggest that it is possible to have "late-onset" ADHD, and patients in the study with this form of the disorder had high levels of symptoms, impairment and other mental health disorders.
"We were very interested by 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."
The team examined a sample of more than 2,200 British twins from the Environmental Risk (E-Risk) Longitudinal Twin Study who had been assessed for childhood ADHD through mother and teacher reports at the ages of 5, 7, 10 and 12.
Since the study examined twins, the researchers were able to shed light on the genetic basis of ADHD, revealing the adult ADHD is less heritable than childhood ADHD. Furthermore, having a twin with childhood ADHD did not have an effect on 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.
