Adults presenting with symptoms of ADHD may not have a childhood-onset neurodevelopmental disorder, reports a recent study conducted in New Zealand.
The prospective, longitudinal Dunedin Multidisciplinary Health and Development Study* performed follow-back analyses on patients diagnosed with ADHD at age 38 years (adult-onset; n=31) alongside follow-forward analyses on patients diagnosed with ADHD at ages 11, 13 or 15 years (child-onset; n=61), and tested whether correlates of adult ADHD match those of childhood ADHD.† Subjects without ADHD (n=920) were also evaluated for comparison.
Key results indicated that patients with child- and adult-onset ADHD comprised virtually non-overlapping sets: follow-forward analyses showed that a minority (n=3; 5%) of child-onset patients met ADHD criteria at the age of 38 years; and follow-back analyses found that these three patients represented only 10% of those with adult-onset ADHD. However, child-onset patients that did not meet criteria for adult ADHD still reported ADHD symptoms as causing mild impairment in their adult lives. Furthermore, the mean IQ of these patients remained 10 points below average in adulthood. Although patients with adult-onset ADHD did not report such cognitive difficulties, they did show high rates of alcohol/drug dependence (48.4%) and tobacco dependence (38.7%), and 48.4% had taken medication for depression, anxiety, psychological trauma, substance treatment or eating disorder.
Additionally, whilst patients with child-onset ADHD exhibited elevated symptoms of ADHD before the age of 12 as reported by parents and teachers (effect size [ES]: 1.60), the adult-onset patients were reported to have only mildly elevated symptoms in comparison to the non-ADHD group (ES: 0.33). Both child-onset and adult-onset patients had elevated rates of conduct disorder as children compared with comparison subjects, however, they were more prevalent in child-onset patients versus adult-onset patients (59% vs 31%).
Finally, a genome-wide polygenic risk score for childhood ADHD was significantly elevated in child-onset (p=0.042) but not adult-onset (p=0.728) patients.
Researchers concluded that the adult syndrome did not appear to represent a continuum from child-onset ADHD, suggesting that ‘adult ADHD’ may be a completely distinct disorder. There were several limitations to this study, including: childhood ADHD was assessed using the DSM-III (which was current at the time); the adult ADHD group was small, which limited statistical power; and ADHD was not assessed in patients in their twenties, thus limiting the ability to trace decline in symptoms for childhood cases. Further studies are therefore required to support these findings.
Read more about adult-onset ADHD here
*This was a longitudinal study of health and behaviour in a representative birth cohort of 1,037 individuals born between April 1972 and March 1973 in Dunedin, New Zealand. The cohort was assessed at birth and at ages 3, 5, 7, 9, 11, 13, 15, 18, 21, 26, 32 and, most recently, 38.
†This included symptoms of ADHD (children assessed for ADHD as per DSM-III criteria; and adults assessed for ADHD as per DSM-5TM criteria [note that the DSM criterion ‘Age of onset before 12 years’ was not asked of adult patients as retrospective recall of psychiatric symptoms across decades has poor validity]), associated clinical features, comorbid disorders, neuropsychological deficits, genome-wide association, study-derived polygenic risk and life impairment.
Moffitt TE, Houts R, Asherson P, et al. Is adult ADHD a childhood-onset neurodevelopmental disorder? Evidence from a four-decade longitudinal cohort study. Am J Psychiatry 2015; 172: 967-977.