The developmental course of ADHD symptoms is influenced by a set of genes that are distinct from genes that govern baseline levels of symptoms, which may explain why ADHD symptoms persist in some children but decline in others, a UK study suggests.
This prospective study examined the proportional impact of genes and the environment on the developmental trajectory of key ADHD symptom domains (i.e. hyperactivity/impulsivity and inattention) within a population-based sample of twins (n=8395 twin pairs).* Latent growth curve models were used to examine the developmental course of hyperactivity/impulsivity and inattention symptoms over an 8-year period. Inattentive and hyperactive/impulsive symptoms were rated by the children’s mothers using both CPRS-R† and DSM-IV‡ ADHD symptom subscales at four time-points (at mean ages: 7.9 years, 11.3 years, 14.1 years and 16.3 years).
The study found that hyperactive and impulsive symptoms declined sharply between the ages of 8 and 16 years, with inter-individual differences in this linear change under strong additive genetic influences (81%). The age-associated reduction in inattention symptoms was less pronounced, with non-additive genetic influences accounting for 54% of the variation in the developmental course of these symptoms. For both hyperactive-impulsive and inattention symptoms, more than half of genetic influences present (additive or non-additive, respectively) were specific to the developmental course and not shared with baseline levels of symptoms.
These findings suggest that different sets of genes may be associated with the developmental course versus the baseline levels of ADHD symptoms, offering a potential explanation for why some children remit from ADHD and others persist. The limited applicability of this population-based study to a clinical ADHD population should be taken into consideration when interpreting these data.
*Participants were drawn from the Twins Early Development Study, a longitudinal study of twin pairs recruited from population records in England and Wales
†Conners’ Parent Rating Scale-Revised
‡Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition
Pingault JB, Viding E, Galéra C, et al. Genetic and environmental influences on the developmental course of attention-deficit/hyperactivity disorder symptoms from childhood to adolescence. JAMA Psychiatry 2015; 72: 651-658.