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The burgeoning number of studies of genetic and environmental risk factors for autism (e.g., Nature Genetics 2010; 42:489; and Arch Gen Psychiatry 2011 Jul 4 (e-pub ahead of print)) have paralleled the growing number of reports of increased prevalence among U.S., European, and Asian populations (e.g., JW Psychiatry Jun 6 2011). Genetic variations alone are unlikely to increase prevalence because population genomes would not change so quickly.
These researchers investigated environmental versus inherited effects in a birth cohort of twin pairs from the California developmental disabilities system, of whom at least one was diagnosed with autism. The investigators used research criteria (comprehensive parental interviews and child assessments) …