Inhibitory Control and Attention Deficit Hyperactivity Disorder (ADHD) in Childhood: Evidence from Two Multi-method, Longitudinal Twin Studies

In childhood, low levels of inhibitory control (IC) are associated with externalizing behavior problems and Attention Deficit Hyperactivity Disorder (ADHD). Multiple twin studies indicate that IC is genetically influenced,... [ view full abstract ]

In childhood, low levels of inhibitory control (IC) are associated with externalizing behavior problems and Attention Deficit Hyperactivity Disorder (ADHD). Multiple twin studies indicate that IC is genetically influenced, however; findings depend somewhat on the age of the participants and the assessment methodology (Gagne & Saudino, 2010; 2016; Gagne & Goldsmith, 2011). For example, two of these studies show evidence for shared environmental influences and non-significant genetic influences on lab-based assessments of IC at age 3. However, parent-ratings of IC show a much more stable and consistent etiology and developmental trajectory. Genetic and environmental covariance between IC and externalizing behavior problems has also been noted in toddlers (Gagne, Saudino & Asherson, 2011) and school age children (Lemery-Chalfant, Doelger, Goldsmith, 2008). We investigated the development and etiology of IC and ADHD behavior problems and symptoms from a multi-method perspective in two independent twin samples. Using both datasets allows us the ability to examine IC development and behavioral maladjustment within early childhood and longitudinally from toddlerhood, through school transition, to early adolescence.

Participants included 300 twin pairs (half MZ), 2 and 3 years of age, from the Boston University Twin Project (BUTP) and between 143-237 MZ and 237-401 DZ twin pairs (samples sizes differ) at 2.5 years, early school age, and early adolescence from the Wisconsin Twin Project (WTP). In the BUTP, parents rated IC and externalizing and ADHD behavior problems, and a lab-based assessment of IC was collected at both ages. In the WTP, mothers rated IC in todderhood and first grade, and ADHD symptoms in first grade and early adolescence. In first grade, an observational measure of IC similar to that used in the BUTP was obtained. Phenotypic correlations between IC and behavior problems and ADHD symptoms ranged from -.10 to -.68. MZ correlations exceeded DZ correlations for most traits, indicating genetic influences. In addition, MZ cross-twin, cross-trait twin correlations between IC and ADHD generally exceeded DZ correlations indicating significant genetic covariance between IC and ADHD across age. Initial bivariate Cholesky decompositions of BUTP age 2 IC (both parent- and lab-assessed) and ADHD behavior problems, WTP parent-rated toddler IC and first grade ADHD, and WTP parent-rated first grade IC and early adolescent ADHD yielded genetic and nonshared environmental variances and covariances. Toddler IC was phenotypically and etiologically associated with concurrent ADHD behavior problems and ADHD in first grade, as was first grade IC and early adolescent ADHD. Based on these findings, early IC can be considered a genetic risk factor for later ADHD symptoms. Future genetic analyses will include IC and ADHD behavior problems data from the BUTP at age 3, and laboratory-based behavioral assessments of IC and measures of home environment from WTP in early school age.