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Childhood neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and intellectual disability (ID) typically are complex, heterogeneous, conditions that show considerable clinical overlap.1 There are both genetic and environmental contributions to their aetiology, which are not yet fully elucidated. However, immense progress has been made in our understanding of their genetic basis in the last two decades. This short review aims to synthesise the key findings in this regard, with a focus on some of the factors that are most relevant to clinical practice.
Family and twin studies provided the first evidence of the familial aggregation and heritability of childhood neurodevelopmental disorders. For example, the heritability estimate for ADHD is 88%2 and for ASD it is 64%–91%.3 Families often want to know the likelihood of having a child with a neurodevelopmental problem in future if they themselves or their offspring have a neurodevelopmental disorder. First-degree relatives of people with ADHD have a five to ninefold elevated risk of having ADHD themselves,4 and siblings of those with ASD are estimated to have a 10-fold elevated risk of having ASD.5 Family studies also show shared genetic effects across disorders,6 that is, siblings of a person with one disorder (eg, ADHD) are themselves at elevated risk of both that disorder and other neurodevelopmental conditions (eg, ASD, reading disability), as well as of subthreshold traits.7 8 These factors mean that parents of children with a neurodevelopmental disorder may show elevated levels of neurodevelopmental traits that do not necessarily meet criteria for a diagnosed disorder. These characteristics could have impact on clinical assessment and parental …
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