Immaturity has been implicated as a possible component of ADHD. To test the possible role of immaturity, Brikell et al. (2016) obtained Swedish parents’ ratings of 1,302 pairs of 8-9-year-old twins’ immaturity relative to average children of the same age. The ratings of relative immaturity (RI) were analyzed in relation to parents’ CBCL ratings of the twins at ages 8-9, 13-14, and 16-17, plus parents’ ABCL ratings of the twins at ages 19-20. The parents’ RI ratings were also analyzed in relation to the twins’ YSR ratings at ages 13-14 and 16-17, as well as their ASR ratings at ages 19-20. ADHD problems were measured with CBCL, YSR, ABCL, and ASR Attention Problems syndrome scores and DSM-oriented ADH Problems scores. (The CBCL/YSR item Acts too young for age was omitted from the attention problems scores.) Brikell et al. found that ratings of RI (predominantly influenced by genes) explained 10-14% of variance in attention problems from ages 8-17 years, falling to 4% at 19-20 years. Other genetic influences explained 19-30% of variance in attention problems from age 13-14 to 19-20 years.
The authors concluded that “some of the genetic influences on attention problems are shared with genetic factors related to RI” but “the magnitude of the association between RI and ADHD symptoms was small across ages, suggesting that RI is best viewed as merely one factor among many that contributes to increased ADHD symptoms” (p. 890).
Brikell, I., et al. (2016). Relative immaturity in childhood and Attention-Deficit/Hyperactivity Disorder symptoms from childhood to early adulthood: Exploring genetic and environmental overlap across development. Journal of the American Academy of Child and Adolescent Psychiatry, 55, 886-895.