Study Uses Identical Twins to Investigate Environmental Influences on the Etiology of ASD
Nonshared environmental effects (NSE) are exposures unique to different children within the same family. NSE, or indicators of NSE, include prenatal factors such as gestational hypertension and diabetes, gestational bleeding, or maternal use of medications; perinatal factors such as breech presentation, fetal distress, preterm birth, cesarean delivery, birth complications, or birth weight; and postnatal factors such as infections and medication and/or antibiotic use. A new study, published in Molecular Autism, has investigated NSEs and their influence on the development of autism. To conduct this study, the authors utilized a monozygotic co-twin study design that was applied to a sample of 224 twins (mean age = 17.70 years). The study controlled for confounding variables such as genes and shared environment. Generalized estimating equation models were developed, using perinatal and postnatal indications of NSEs as exposure, operationalized both as separate risk factors as well as cumulative risk loads. The study’s results demonstrated that birth weight discordance was associated with autism and ADHD for the smaller twin. For postnatal NSE, medication exposure during infancy was associated with autism. Twins who experienced postnatal convulsions had more autism traits. At a diagnostic level, only those with a diagnosis of autism, ADHD, or intellectual disability reported convulsions within discordant pairs. Additionally, frequent ear infections and head injury were associated with traits of autism, whereas scarlet fever and jaundice were associated with lower IQ. In the end, the researchers believe their findings suggest that autism may be exceptionally sensitive to a cumulative early environmental risk load.
