Abstract
Neurodevelopmental disorders represent a broad class of childhood neurological conditions that have a significant bearing on the wellbeing of children, families, and communities. In this review, we draw on evidence from two common and widely studied neurodevelopmental disorders—autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD)—to demonstrate the utility of genetically informed sibling designs in uncovering the nature and pathogenesis of these conditions. Specifically, we examine how twin, recurrence risk, and infant prospective tracking studies have contributed to our understanding of genetic and environmental liabilities towards neurodevelopmental morbidity through their impact on neurocognitive processes and structural/functional neuroanatomy. It is suggested that the siblings of children with ASD and ADHD are at risk not only of clinically elevated problems in these areas, but also of subthreshold symptoms and/or subtle impairments in various neurocognitive skills and other domains of psychosocial health. Finally, we close with a discussion on the practical relevance of sibling designs and how these might be used in the service of early screening, prevention, and intervention efforts that aim to alleviate the negative downstream consequences associated with disorders of neurodevelopment.
Highlights
Neurodevelopmental disorders represent a broad class of childhood neurological conditions that have a significant bearing on the wellbeing of children, families, and communities
We draw on evidence from two common and widely studied neurodevelopmental disorders—autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD)— to demonstrate the utility of genetically informed sibling designs in uncovering the nature and pathogenesis of these conditions
It is suggested that the siblings of children with ASD and ADHD are at risk of clinically elevated problems in these areas, and of subthreshold symptoms and/or subtle impairments in various neurocognitive skills and other domains of psychosocial health
Summary
Neurodevelopmental disorders are brain-based disorders of growth and development that have a significant impact on children’s mental, emotional, and psychosocial health. In a sample of DZ twins discordant for ADHD diagnosis, it was shown that unaffected cotwins of children with ADHD were significantly impaired in many neuropsychological domains, including executive functioning, processing speed, and arousal regulation compared to controls, even after controlling for subclinical levels of ADHD symptoms [75] These results suggest that neurocognitive deficits in these domains may serve as plausible endophenotypes in the etiology of ADHD. These results corroborate early reports of the familygenetic risk of ADHD and intellectual impairment in the siblings of children with ADHD [90, 91] They are consistent with related avenues of research showing that the siblings of children with ADHD are at an increased risk of developing a host of other psychological and psychiatric problems, including disruptive behaviour problems [92, 93], affective disorders, and anxiety problems [89] compared to either control siblings or population prevalence rates. By comparing high-risk infants who do and do not develop ADHD on differentiating factors, we can further delineate the constitutional and/or environmental moderators that interact to influence the emergence, persistence, and remission of the disorder [116]
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