Nearly 70 percent of young adults who have attention deficit hyperactivity disorder (ADHD) were not diagnosed with the condition in childhood, say researchers at King’s College London in the United Kingdom. The study was announced, and were published online in the journal JAMA Psychiatry. Another study from Brazil supports the UK research.
These findings challenge the common belief that adult ADHD is a continuation of the disorder from childhood and suggests that the onset of the condition may have different causes than childhood ADHD. Adults with a late-onset diagnosis have higher levels of impairment, symptoms, and other mental health disorders.
Researchers studied more than 2,200 British twins who participated in the Environmental Risk (E-Risk) Longitudinal Twin Study. ADHD symptoms were measured at the ages of five, seven, 10, and 12 based on reports by mothers and teachers. Young adults at age 18 were interviewed to assess ADHD symptoms, associated impairments, and other mental health disorders. The genetic basis of the disorder was also examined. Less adults inherited adult ADHD than those who inherited childhood ADHD. Having a twin with childhood ADHD did not put the sibling at a higher risk of developing the condition later on.
“We were very interested by this large ‘late-onset’ ADHD group, as ADHD is generally seen as a childhood-onset neurodevelopmental disorder,” said Dr Jessica Agnew-Blais from the IoPPN at King’s College London. “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. We think it is important that we continue to investigate the underlying causes of late-onset ADHD.”
Approximately four percent of adults are diagnosed with this disorder but only a few adults are diagnosed and treated. “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, Professor Louise Arseneault, also from the IoPPN at King’s College London, said. “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.”
