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Adults with ADHD may not have had onset of disorder in childhood

Adult attention-deficit/hyperactivity disorder may not originate in childhood and may have a distinct etiology than the childhood disorder, according to recent findings.

In the prospective, longitudinal study, researchers evaluated 1,037 individuals born in Dunedin, New Zealand in 1972 and 1973, who were participants in Multidisciplinary Health and Development Study, an analysis of health and behavior in a complete birth cohort. Participants were followed to age 38. Children with ADHD were identified through the Dunedin Study’s group of children and diagnosed at ages 11, 13 and 15, between 1984 and 1988 (n = 61). A child psychiatrist identified symptoms of ADHD in the children aged 11 and 13 years using the Diagnostic Interview Schedule for Children-Child Version, and trained reviewers identified symptoms at age 15.

In adults, ADHD symptoms were determined through structured diagnostic interviews by clinically experienced, trained interviewers who were blinded to previous data. The interviews were conducted when participants were 38 years of age. The 27-item interviews were used to operationalize the 18 symptoms of ADHD included in the DSM-5. The researchers identified 31 adult cases of ADHD. A comparison group consisting of 920 participants who had never been diagnosed with ADHD in the Dunedin study was also included for analysis.

The researchers evaluated 50 ADHD correlates listed in the DSM-5, including comorbid conditions, neuropsychological impairments, genome-wide association study-derived polygenic risk, and life impairment indicators. They determined if the correlates for childhood ADHD were the same as those for adult ADHD.

They found a 6% prevalence of ADHD in children, primarily boys. Childhood ADHD was associated with comorbid disorders, neurocognitive abnormalities, polygenic risk and ongoing life impairment. The prevalence of adult ADHD was 3%, with parity between genders. Adult ADHD was found to be correlated with substance addiction, adult life impairment, and presentation for mental health treatment. In an unanticipated finding, the childhood and adult ADHD groups barely overlapped, with 90% of adult cases having no history of ADHD as children. Moreover, the adult ADHD cohort did not demonstrate tested neuropsychological abnormalities in childhood or adulthood, and did not exhibit polygenic risk for childhood ADHD.

“Unfortunately, the assumption that adult ADHD is the same as childhood ADHD and therefore that its causes have already been researched may be discouraging etiological research into adult ADHD,” the researchers wrote. “If our finding of no childhood-onset neurodevelopmental abnormality for the majority of adult ADHD cases is confirmed by others, then the etiology for adults with an ADHD syndrome will need to be found.” – by Jennifer Byrne

Disclosures: Please see the full study for a list of relevant disclosures.