An autism spectrum disorder (ASD) is a complex neurological disorder that interferes with the normal course of social, communicative, and cognitive development. The Los Angeles County Department of Public Health contains a specific Regional Center to provide services to children with autism. The diagnosis of autism is made in early childhood; symptoms appear within the first three years of life. Over the last three decades, the prevalence of autism has increased substantially: from 4 to 5 per 10,000 in the 1960s to approximately 40 per 10,000 children today. Two recent studies have unearthed two interesting factors: children of mothers who took an antidepressant any time in the year before delivery have a higher risk of autism; and environmental factors appear to be more important than genetics.
A study published online in the Archives of General Psychiatry on July 4, 2011 examined records of twin pairs obtained from the Department of Developmental Services (DDS). The DDS operates a system of 21 regional centers throughout California that coordinate services for persons with autism, mental retardation, and other developmental disabilities. Autism is considered to be the most heritable of neurodevelopmental disorders, mainly because of the large difference in concordance rates (both individuals affected) between monozygotic (identical) and dizygotic (fraternal) twins. The goal of the study was to determine quantitative estimates of genetic heritability of autism and the effects of shared environment. The study group was comprised of twin pairs in which at least one twin with an ASD born between 1987 and 2004 were identified through the California DDS.
Structured diagnostic assessments were completed on 192 twin pairs. Concordance rates were calculated and two groups were identified: narrow (strict autism) and broad (ASD). The researcher found that for strict autism, concordance for male twins was 0.58 for 40 monozygotic pairs and 0.21 for 31 dizygotic pairs; for female twins, the concordance was 0.60 for seven monozygotic pairs and 0.27 for 10 dizygotic pairs. For ASD, the concordance for male twins was 0.77 for 45 monozygotic pairs and 0.31 for 45 dizygotic pairs; for female twins, the concordance was 0.50 for nine monozygotic pairs and 0.36 for 13 dizygotic pairs. The authors noted that a large proportion of the variation in development of autism can be explained by shared environmental factors. They also found a moderate genetic heritability.
The authors concluded that the susceptibility to ASD has moderate genetic heritability and a substantial shared twin environmental component. Thus, environmental factors, including exposure to drugs, play a greater role in ASD than genetics.
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