The opposite end of the attention deficit hyperactivity disorder continuum: genetic and environmental aetiologies of extremely low ADHD traits.

Corina U Greven,Claire M A Haworth,Jan K Buitelaar,Nanda Rommelse,Jolanda M J Van Der Meer,Andrew Merwood

doi:10.1111/jcpp.12475

Abstract

BackgroundAlthough attention deficit hyperactivity disorder (ADHD) is thought to reflect a continuously distributed quantitative trait, it is assessed through binary diagnosis or skewed measures biased towards its high, symptomatic extreme. A growing trend is to study the positive tail of normally distributed traits, a promising avenue, for example, to study high intelligence to increase power for gene‐hunting for intelligence. However, the emergence of such a ‘positive genetics’ model has been tempered for ADHD due to poor phenotypic resolution at the low extreme. Overcoming this methodological limitation, we conduct the first study to assess the aetiologies of low extreme ADHD traits.MethodsIn a population‐representative sample of 2,143 twins, the Strength and Weaknesses of ADHD Symptoms and Normal behaviour (SWAN) questionnaire was used to assess ADHD traits on a continuum from low to high. Aetiological influences on extreme ADHD traits were estimated using DeFries–Fulker extremes analysis. ADHD traits were related to behavioural, cognitive and home environmental outcomes using regression.ResultsLow extreme ADHD traits were significantly influenced by shared environmental factors (23–35%) but were not significantly heritable. In contrast, high‐extreme ADHD traits showed significant heritability (39–51%) but no shared environmental influences. Compared to individuals with high extreme or with average levels of ADHD traits, individuals with low extreme ADHD traits showed fewer internalizing and externalizing behaviour problems, better cognitive performance and more positive behaviours and positive home environmental outcomes.ConclusionsShared environmental influences on low extreme ADHD traits may reflect passive gene‐environment correlation, which arises because parents provide environments as well as passing on genes. Studying the low extreme opens new avenues to study mechanisms underlying previously neglected positive behaviours. This is different from the current deficit‐based model of intervention, but congruent with a population‐level approach to improving youth wellbeing.

Highlights

Attention deficit hyperactivity disorder as a quantitative trait Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder affecting around 6–7% of children and adolescents (Willcutt, 2012)
Background: attention deficit hyperactivity disorder (ADHD) is thought to reflect a continuously distributed quantitative trait, it is assessed through binary diagnosis or skewed measures biased towards its high, symptomatic extreme
DeFries–Fulker extremes analyses showed that, across 5%, 10%, 15% and 20% cut-offs, h2g was significant for high extreme (h2g = 39–51%), but not for low extreme ADHD traits

Summary

Introduction

Attention deficit hyperactivity disorder as a quantitative trait Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder affecting around 6–7% of children and adolescents (Willcutt, 2012). Traditional interview and questionnaire measures allow fine-scaled assessment of variability at the high extreme of mental health continua, but attenuate variability at the low, unaffected end, reflected in skewed measure distributions. Overcoming this methodological limitation, this is the first study to assess the genetic and environmental aetiologies of low extreme ADHD scores. The emergence of such a ‘positive genetics’ model has been tempered for ADHD due to poor phenotypic resolution at the low extreme Overcoming this methodological limitation, we conduct the first study to assess the aetiologies of low extreme ADHD traits.

Methods

Results

Discussion

Conclusion