Does the Environment Have an Enduring Effect on ADHD? A Longitudinal Study of Monozygotic Twin Differences in Children

Abstract

Environmental factors play a key role in the development of Attention-Deficit/Hyperactivity Disorder (ADHD), but the long-term effects of these factors are still unclear. This study analyses data from 1024 monozygotic (identical) twins in Australia, the United States, and Scandinavia who were assessed for ADHD in Preschool, Kindergarten, Grade 1, and Grade 2. Differences within each twin pair were used as a direct measure of non-shared environmental effects. The Trait-State-Occasion (TSO) model developed by Cole, Martin, and Steiger (2005) was used to separate the non-shared environmental effects into stable factors, and transient factors that excluded measurement error. Stable factors explained, on average, 44% and 39% of the environmental variance in hyperactive-impulsive and inattentive symptoms, respectively. Transient effects explained the remaining 56% and 60% of variance. The proportion of stable variance was higher than expected based on previous research, suggesting promise for targeted interventions if future research identifies these stable risk factors.

Genetic and phenotypic evidence of the predictive validity of preschool parent reports of hyperactivity/impulsivity and inattention

“…Unique environment factors contributed substantially to individual differences in ) and to a lesser extent in HI (.22-.50), more so than in previous studies. There are two predominant patterns of environmental influences on ADHD: transient effects contributing to single measurement occasions and stable effects that persist over time (Livingstone et al, 2016). As in previous studies, we found mostly transient unique environment factors (Chang et al, 2013;Faraone et al, 2015;Greven et al, 2011;Kuntsi et al, 2005;Larsson et al, 2004Larsson et al, , 2014Pingault et al, 2015).…”

Time-varying and time-invariant dimensions of depression in children and adolescents: Implications for cross-informant agreement.

“…These might also include stable environmental factors (Conway et al, 2016; Kendler et al, 2011). An interesting find was that twin studies of depression have partitioned the variance of depression into that which is because of shared genetics and that which is because of shared environmental factors (Ask, Waaktaar, Seglem, & Torgersen, 2016; Eley & Stevenson, 1999; Muthén & Muthén, 1998–2010; Matthews et al, 2016; Rice, Harold, & Thapar, 2002; Tackett Waldman, Van Hulle, & Lahey, 2011; Zheng, Rijsdijk, Pingault, McMahon, & Unger, 2016; see also Livingstone et al, 2016). Both sets of estimates vary substantially (partially as a function of age or developmental level), with estimates of genetic contributions ranging from 2 to 57% (median = 21.5%) and estimates of shared environmental effects ranging from 1 to 38% (median = 36.5%); however, their combined effects are quite reliable (with a median of 52.5% and a range of 39% to 62%).…”

Externalizing problems in childhood and adolescence predict subsequent educational achievement but for different genetic and environmental reasons

“…This result is notable in light of the rarity of nonshared‐environmental stability over time (e.g. Burt, Klahr, & Klump, ; Turkheimer & Waldron, ; although see Livingstone et al., ). The link between early‐childhood anxiety and peer problems and later educational achievement was explained by shared‐environmental factors.…”