Genes influence ADHD course

By Eleanor McDermid, Senior medwireNews Reporter

A large twin study shows that genetics have a major influence on whether attention deficit/hyperactivity disorder (ADHD) symptoms decrease or persist as children grow older.

Furthermore, these genetic influences are mostly separate from those that determine severity of symptoms at baseline, report Jean-Baptiste Pingault (University College London, UK) and study co-authors.

“The confirmation of large genetic influences on the developmental course of ADHD symptoms is important for both clinicians and patients”, they write in JAMA Psychiatry. “For clinicians, the maintenance or increase in symptoms (a decline being normative in the population) might represent a marker of vulnerability reflecting genetic liability and warrant closer follow-up.”

The parents of the study participants – 8395 twin pairs – rated their children’s ADHD symptoms on the Conners’ Parent Rating Scales–Revised when they were aged an average of 7.9, 11.3, 14.1 and 16.3 years.

Findings differed for hyperactivity/impulsivity and for inattention symptoms, with the former being governed mostly by additive genetic effects and decreasing markedly over time, whereas the latter were more influenced by dominant genetic effects and remained fairly stable over time.

At age 8, the children had an average hyperactivity/impulsivity score of 6.0, and the researchers’ models showed that 90% of the variance was explained by additive genetic influences.

Indeed, additive genetic influence “was pervasive at all ages”, writes the team. It accounted for about 80% of the total variance in hyperactivity/impulsivity scores at all ages.

The average hyperactivity/impulsivity score decreased to 2.9 by age 16 years, and 81% of the variance in change of score was accounted for by additive genetic influences. This comprised 37% that also influenced baseline scores and 44% that was specific to the change over time, meaning that more than half of the genetic influences on change over time did not affect scores at baseline.

Inattention scores changed only slightly, from an average of 5.8 at age 8 years to 4.9 at age 16 years. And rather than being explained almost entirely by additive genetic effects, 55% of the variance in baseline scores were accounted for by dominant genetic effects, as was 54% of the change over time.

Again, more than half of the dominant genetic effects that influenced change over time did not affect baseline inattention scores.

“Developmental models will be crucial in identifying genetic variants and specific environmental influences explaining why some children remit from ADHD, whereas others persist”, concludes the team.

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