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What causes attention deficit hyperactivity disorder?
  1. Anita Thapar1,2,
  2. Miriam Cooper1,2,
  3. Rachel Jefferies1,2,
  4. Evangelia Stergiakouli1,2
  1. 1Department of Psychological Medicine and Neurology, Cardiff University School of Medicine, Cardiff, UK
  2. 2MRC Centre in Neuropsychiatric Genetics and Genomics, Cardiff University, Cardiff, UK
  1. Correspondence to Anita Thapar, Child and Adolescent Psychiatry Section, Department of Psychological Medicine and Neurology, Cardiff University, School of Medicine, Heath Park, Cardiff, CF14 4XN, UK; thapar{at}


Attention deficit hyperactivity disorder (ADHD) affects around 1–3% of children. There is a high level of comorbidity with developmental and learning problems as well as with a variety of psychiatric disorders. ADHD is highly heritable, although there is no single causal risk factor and non-inherited factors also contribute to its aetiology. The genetic and environmental risk factors that have been implicated appear to be associated with a range of neurodevelopmental and neuropsychiatric outcomes, not just ADHD. The evidence to date suggests that both rare and multiple common genetic variants likely contribute to ADHD and modify its phenotype. ADHD or a similar phenotype also appears to be more common in extreme low birth weight and premature children and those exposed to exceptional early adversity. In this review, the authors consider recent developments in the understanding of risk factors that influence ADHD.

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  • Competing interests None.

  • Provenance and peer review Commissioned; externally peer reviewed.