Journal
DEVELOPMENT AND PSYCHOPATHOLOGY
Volume 33, Issue 4, Pages 1448-1495Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0954579420000620
Keywords
confounding factors; environmental exposure; neurodevelopmental disorders; systematic review; systematic review; twin and sibling studies
Categories
Funding
- PRIMA Child and Adult Psychiatry AB Research
- Faculty of Medicine at Uppsala University Foundation for Psychiatric and Neurologic Research
- Sven Jerring Foundation
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Neurodevelopmental disorders (NDDs) are influenced by both genetics and environmental factors, with familial confounding potentially impacting research outcomes. More genetically informed studies are needed to better understand the environmental causes of NDDs.
While neurodevelopmental disorders (NDDs) are highly heritable, several environmental risk factors have also been suggested. However, the role of familial confounding is unclear. To shed more light on this, we reviewed the evidence from twin and sibling studies. A systematic review was performed on case control and cohort studies including a twin or sibling within-pair comparison of neurodevelopmental outcomes, with environmental exposures until the sixth birthday. From 7,315 screened abstracts, 140 eligible articles were identified. After adjustment for familial confounding advanced paternal age, low birth weight, birth defects, and perinatal hypoxia and respiratory stress were associated with autism spectrum disorder (ASD), and low birth weight, gestational age and family income were associated with attention-deficit/hyperactivity disorder (ADHD), categorically and dimensionally. Several previously suspected factors, including pregnancy-related factors, were deemed due to familial confounding. Most studies were conducted in North America and Scandinavia, pointing to a global research bias. Moreover, most studies focused on ASD and ADHD. This genetically informed review showed evidence for a range of environmental factors of potential casual significance in NDDs, but also points to a critical need of more genetically informed studies of good quality in the quest of the environmental causes of NDDs.
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