The role of birth weight on the causal pathway to child and adolescent ADHD symptomatology: a population‐based twin differences longitudinal design

Abstract

BackgroundAvailable evidence points towards lower birth weight as a risk factor for the development of attention deficit/hyperactivity disorder (ADHD) symptoms. We probed the causal nature of this putative effect of birth weight on ADHD symptoms using the twin differences design, which accounts for genetic and shared environmental confounds.MethodIn a large population‐based twin sample – 3,499 monozygotic (MZ) and 6,698 dizygotic (DZ) pairs – parents, teachers or twins rated the twins’ ADHD symptoms at nine assessment waves (2–16 years). We implemented the twin differences design, which completely accounts for shared environmental and genetic confounding in MZ twins. We tested whether: (a) the lighter‐born twins had elevated ADHD symptoms compared to the heavier‐born twins, by regressing within‐pair differences of ADHD symptoms on within‐pair differences of birth weight among MZ twins; (b) the effect of birth weight on ADHD was moderated by gender, gestational age and low birth weight; (c) this effect changed with age at ADHD assessment using adapted latent growth curve models; and (d) results differed for inattention and hyperactivity/impulsivity.ResultsBirth weight significantly predicted ADHD symptoms from early childhood to late adolescence. The lighter‐born twin had more ADHD symptoms than the heavier‐born cotwin among MZ twins across assessment waves and raters. No moderation effect was detected. The magnitude of the effect of birth weight decreased significantly across time for hyperactivity/impulsivity, but the decrease failed to reach significance for inattention. Estimates for inattention were significantly larger than for hyperactivity/impulsivity at each time point, implying stronger effect of birth weight on inattention symptoms.ConclusionsOur findings provide stringent evidence for environmental effect of lower birth weight on the causal pathway to elevated ADHD symptoms. Effect of birth weight persists across a 14‐year period from childhood into late adolescence, in particular for inattention symptoms.

The p factor: genetic analyses support a general dimension of psychopathology in childhood and adolescence

“…Notably, some interesting results also emerge about the environment. There are some known general ‘environmental’ risks for psychopathology such as birthweight, birth complications and childhood maltreatment that are associated with diverse neurodevelopmental outcomes (Caspi & Moffitt, ; Lim et al., ). However, we find that nonshared environmental effects contribute less than genetic effects to the general psychopathology factor and its temporal stability.…”

Birth weight is associated with adolescent brain development: A multimodal imaging study in monozygotic twins

“…Interestingly, studies of MZ twin pairs have shown that the lower BW twin has lower intelligence quotient scores, relative to the higher BW twin (Edmonds et al, 2010; Newcombe, Milne, Caspi, Poulton, & Moffitt, 2007). Other studies have found that greater BW discordance was associated with greater within‐pair differences in child problematic behavior (Lim et al, 2018; Tore et al, 2018; van Os et al, 2001). We and others have previously found in MZ twin pairs that overall brain volume and cortical surface area were positively associated with BW discordance in frontal and temporal brain regions in adolescents and adults (Casey et al, 2017; Levesque et al, 2015; Raznahan, Greenstein, Lee, Clasen, & Giedd, 2012).…”

“…Interestingly, studies of MZ twin pairs have shown that the lower BW twin has lower intelligence quotient scores, relative to the higher BW twin (Edmonds et al, 2010;Newcombe, Milne, Caspi, Poulton, & Moffitt, 2007). Other studies have found that greater BW discordance was associated with greater within-pair differences in child problematic behavior (Lim et al, 2018;Tore et al, 2018;van Os et al, 2001).…”

Twins and Causal Inference: Leveraging Nature's Experiment

“…The co-twin control design has been widely used for causal inference, confirming for example the causal link between smoking and lung cancer (Hjelmborg et al, 2017), demonstrating the impact of bullying victimisation on childhood mental health (Silberg et al, 2016), and suggesting that birth weight impacts the development of ADHD symptoms (Lim et al, 2018). Findings from the co-twin design can shed new light on the role of risk factors.…”

“…More elaborate longitudinal models can also be built based on twin differences. For example, a latent growth model has been implemented to show that differences in birth weight predict ADHD symptoms from childhood to adolescence, but that the size of the effect decreases with age, consistent with a partial 'catch-up' effect (Lim et al, 2018). Cross-lag models can be implemented with twin differences to look at reciprocal influences between two phenotypes over time, while controlling for genetic and shared environmental confounding (Cecil, Barker, Jaffee, & Viding, 2012).…”