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Topic Editor: Russell Schachar, MD, University of Toronto, Canada
ADHD is believed to be caused by an interaction of genetic and environmental factors. Symptoms of ADHD are highly heritable (76%), yet the nature of the genetic influence is still unknown. Results from published studies indicate that ADHD shares genetic influences with other conditions so, for example, one finds shared genetic influences between inattentive symptoms and dyslexia, hyperactive-impulsive symptoms and oppositional problems, and ADHD with symptoms of autism. Furthermore, genes responsible for cell division, cell adhesion, and neuronal migration are thought to be related to the onset of ADHD. Among environmental risk factors, researchers have noted the negative influence of prenatal maternal smoking and drinking, maternal depression, low birth weight, poor parenting practices, and living in a disadvantaged neighbourhood.
Children with ADHD experience more academic problems than their schoolmates due to their neuro-cognitive impairments and behaviour. ADHD is often associated with deficits in executive functioning (e.g., planning, organizing, paying attention to important details, and inhibiting impulses). Accordingly, children identified with this disorder are more likely to exhibit learning and/or language disabilities. Results from studies examining the working of the brain suggest that ADHD is associated with atypical activity in the frontal cortex, the brain area responsible for cognitive processes. That said it is important to note that only a subgroup of school-aged children with ADHD (30%) has executive functioning weaknesses, suggesting it is neither necessary nor sufficient to cause the disorder.
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