Developmental Twin Study of Attention Problems

Abstract

The genetic and environmental link between attention-deficit/hyperactivity disorder in childhood and the adult manifestation of the disorder is poorly understood because of a lack of longitudinal studies with crossinformant data. Objective: To explore the relative contribution of genetic and environmental influences on symptoms of attention problems from childhood to early adulthood. Design: Analysis was conducted using longitudinal structural equation modeling with multiple informants. Setting: The Swedish Twin Study of Child and Adolescent Development. Participants: One thousand four hundred eighty twin pairs were prospectively followed up from childhood to young adulthood. Main Outcome Measures: Symptoms were obtained using parent and self-ratings of the Attention Problems Scale at ages 8 to 9, 13 to 14, 16 to 17, and 19 to 20 years. Results: The best-fitting model revealed high heritability of attention problems as indexed by parent and selfratings from childhood to early adulthood (h 2 = 0.77-0.82). Genetic effects operating at age 8 to 9 years continued, explaining 41%, 34%, and 24% of the total variance at ages 13 to 14, 16 to 17, and 19 to 20 years. Moreover, new sets of genetic risk factors emerged at ages 13 to 14, 16 to 17, and 19 to 20 years. Conclusions: The shared view of self-and informantrated attention problems is highly heritable in childhood, adolescence, and early adulthood, suggesting that the previous reports of low heritability for attentiondeficit/hyperactivity disorder in adults are best explained by rater effects. Both genetic stability and genetic innovation were present throughout this developmental stage, suggesting that attention problems are a developmentally complex phenotype characterized by both continuity and change across the life span.

The heritability of clinically diagnosed attention deficit hyperactivity disorder across the lifespan

“…The finding is in line with a recent cross-informant twin study reporting that the heritability of ADHD in 19–20 year olds was 78%, when both self and parent ratings were combined into a composite index of ADHD symptoms to adjust for rater bias (Chang et al, 2013) and also with prior family studies suggesting a high familial loading on ADHD in adults (Biederman et al, 1996, Biederman et al, 1995, Faraone et al, 2000, Faraone, 2004), but is inconsistent with what has been reported in twin studies of self-rated ADHD in adults (Reiersen et al, 2008, Boomsma et al, 2010, van den Berg et al, 2006, Larsson et al, 2013a). One increasingly recognized explanation to previous reports of low heritability for ADHD in adults is increased contribution of measurement error (reflecting accuracy of the measures) associated with the use of self-ratings (Kan et al, 2013, Franke et al, 2012, Merwood et al, 2013, Chang et al, 2013). Another explanation is that the clinical diagnosis of ADHD in adults reflects persistence of the childhood disorder (i.e., childhood onset), whereas cross-sectional self-ratings may also reflect adult-onset ADHD-like symptoms (i.e., phenocopies) involving different genetic and environmental processes.…”

“…This is because twin studies on ADHD in adults have used self-ratings, while studies on children have used other informants (i.e., parent and teacher ratings). The few studies on this topic suggest that the heritability of self-rated ADHD is low in both adults and adolescents (Kan et al, 2013, Merwood et al, 2013), and that the heritability of ADHD in adults is substantial when both self and parent ratings are combined into a composite index of ADHD (Chang et al, 2013). Together, these findings suggest that the low heritability for ADHD in adults may be best explained by rater effects.…”

“…Based on previously observed similarities between continuous trait measures and broad categorical definitions, we predicted similar heritability estimates for clinically diagnosed ADHD. Based on the recent cross-informant twin studies (Chang et al, 2013), we predicted high heritability also for ADHD in adults. This is because both cross-informant measures and clinical diagnosis focus on pervasive symptoms.…”

Childhood predictors of adolescent and young adult outcome in ADHD

“…Finally, the exclusive reliance on parent report as outcome measure in adolescence and young adulthood is also a potential limitation. However, research to date suggests the use of parent ratings of ADHD symptoms as the most reliable source of information compared to self-ratings, in both children and adults (Chang et al , 2013, Epstein et al , 2000, Merwood et al , 2013). Furthermore, we wished to use the same rater for both baseline and outcomes measures as otherwise any observed changes might related to change in the rater (parent to self-report) rather than reflecting the developmental change.…”

Parenting Behavior Mediates the Intergenerational Association of Parent and Child Offspring ADHD Symptoms

“…The intergenerational continuity of ADHD (i.e., parental and offspring ADHD) reflects substantial shared genetic influences: In a meta-analysis of 22 studies, genetic factors accounted for 71% and 73% of the variance in inattention and hyperactivity symptoms, respectively (Nikolas & Burt, 2010). However, imperfect concordance rates of ADHD among monozygotic (MZ) twins indicate the importance of environment influences: Among 1,480 MZ and dizygotic twins, the cross-MZ twin correlations at age 8, 13, 16, and 19 ranged from r =.53 to .70 for parent-rated attention problems and from r =.09 to .33 for self-rated attention problems (Chang, Lichtenstein, Asherson, & Larsson, 2013). Furthermore, only 25 to 50% of parents with ADHD have a biological child with ADHD (Biederman, Faraone, & Monuteaux, 2002; Chronis et al, 2003; Wilens et al, 2005).…”