Analysis of Norwegian families found no convincing evidence that parents’ genes shape ADHD traits indirectly through the home environment at ages five and eight.
A large family study suggests that by mid-childhood, a child’s own genetic make-up may matter more for attention-deficit hyperactivity disorder traits than the indirect influence of parents’ genes through the home environment. Researchers writing in Behavior Genetics found no solid evidence of what scientists call genetic nurture at ages five and eight, although they warned that the statistical noise in the data could still be hiding smaller effects.
ADHD is a neurodevelopmental condition marked by inattention, hyperactivity and impulsivity, and twin studies have long shown that it is highly heritable. That means a child’s DNA is already known to play a major part in the condition. The harder question is whether parents’ genes also shape a child’s behaviour indirectly by influencing parenting style, household routines or other environmental factors. Daniel L. Wechsler of King’s College London led the new analysis in an effort to separate those direct and indirect pathways.
The team drew on the Norwegian Mother, Father and Child Cohort Study, using genetic data from mother-father-child trios alongside parent questionnaires about children’s behaviour. At age five, preliminary models suggested a possible maternal indirect effect, but that signal disappeared in more rigorous tests. By age eight, the strongest fitting model pointed to a direct effect from the child’s own genetics, with no convincing evidence that either parent’s genes were shaping overall ADHD traits through the environment.
The findings do not entirely close the door on genetic nurture. The authors note that the study may not have had enough statistical power to detect subtle indirect effects, especially when looking at broad ADHD scores rather than specific behaviours such as inattention or hyperactivity. They also caution that the ratings came only from mothers and that all of the families in the analysis were of European ancestry, which limits how widely the results can be applied. Even so, the study adds to evidence that a child’s own biology becomes increasingly important as ADHD-related traits emerge and develop.
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