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J Child Psychol Psychiatry. 2016 Apr;57(4):523-31. doi: 10.1111/jcpp.12475. Epub 2015 Oct 17.

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

Author information

1
Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands.
2
Karakter Child and Adolescent Psychiatry University Center, Nijmegen, The Netherlands.
3
Medical Research Council Social, Genetic & Developmental Psychiatry Centre, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.
4
Department of Psychology, University of Bath, Bath, UK.
5
School of Experimental Psychology and School of Social and Community Medicine, MRC Integrative Epidemiology Unit at the University of Bristol, Coventry, UK.
6
Department of Psychiatry, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands.

Abstract

BACKGROUND:

Although 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.

METHODS:

In 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.

RESULTS:

Low 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.

CONCLUSIONS:

Shared 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.

KEYWORDS:

Attention deficit hyperactivity disorder; extremes; positive genetics; quantitative trait; twin

PMID:
26474816
PMCID:
PMC4789118
DOI:
10.1111/jcpp.12475
[Indexed for MEDLINE]
Free PMC Article

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