Attention deficit hyperactivity disorder: a lifespan genetic perspective
| Date | 15 July 2011 |
| Pages | 33-46 |
| DOI | https://doi.org/10.1108/20441281111165599 |
| Published date | 15 July 2011 |
| Author | Andrew Merwood,Philip Asherson |
| Subject Matter | Health & social care,Learning & intellectual disabilities |
Attention deficit hyperactivity disorder:
a lifespan genetic perspective
Andrew Merwood and Philip Asherson
Abstract
Purpose – Attention deficit hyperactivity disorder (ADHD) is a common disorder that is highly prevalent
in children and frequently persists into adulthood. The purpose of this paper is to consider the need for
practitioners to be aware of the disorder.
Design/methodology/approach – This paper reviews quantitative genetic findings in ADHD, primarily
focussing on twin studies that describe the role of genetic influences throughout the lifespan and the
associated overlap between ADHD and other syndromes, disorders and traits.
Findings – This paper concludes that ADHD is a lifespan condition that shares genetic risk factors with
other psychiatric, neurodevelopmental disorders and intellectual disabilities.
Originality/value – This paper makes the case that clinicians working in the area of intellectual disability
should be fully aware of the potential impact of ADHD and its associated impairments.
Keywords ADHD, Genetics, Comorbidity, Developmentalpsychology, Intellectual disability,
Learning disabilities
Paper type Research paper
Introduction
Attention deficit hyperactivity disorder (ADHD) is a complex, neurodevelopmental disorder
characterised by inattentive, hyperactive and impulsive symptoms (APA, 1994). Although
initially recognised as a childhood disorder, it is now established that ADHD frequently
persists into adulthood (Barkley et al., 2008). Recent findings suggest that up to 36 per cent of
childhood ADHD persists into adulthood (Kessler et al., 2006) and around 66 per cent of
adults retain at least some symptoms from childhood (Faraone et al., 2006). ADHD thus
presents throughout the lifespan, prevalent in around 5 per cent of the child population
(Polanczyk et al., 2007) and over 2 per cent of adults (Simon et al., 2009).
Whilst precise causal mechanisms remain unclear, evidence from family, twin and adoption
studies indicates a substantial genetic basis for symptoms of ADHD (Faraone, 2005). Such
quantitative genetic (QG) studies also suggest shared genetic risk factors between ADHD
symptoms and other phenotypes. This paper provides an overview of QG findings and
considers the relevance to intellectual disability practitioners.
The genetic basis of ADHD
Cross-sectional twin studies
Twin studies reveal that ADHD is highly heritable with estimates in the range of 70-80 per
cent (Faraone et al., 2005; Burt, 2009). Heritability is similar for parent and teacher ratings of
ADHD symptoms in children and adolescents (Nikolas and Burt, 2010). A consistent finding
is that the influence of the shared environment is negligible (Burt, 2009), suggesting that
DOI 10.1108/20441281111165599 VOL. 5 NO. 4 2011, pp. 33-46, QEmerald Group Publishing Limited, ISSN 2044-1282
j
ADVANCES IN MENTALHEALTH AND INTELLECTUAL DISABILITIES
j
PAGE 33
Andrew Merwood is a PhD
Student and
Philip Asherson is a
Professor of Molecular
Psychiatry, both are based
at MRC Social Genetic and
Developmental Psychiatry,
Institute of Psychiatry,
King’s College London,
London, UK.
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