July 7, 2011
Pregnancy and Birth Environment May Affect Autism in Twins
(Ivanhoe Newswire) "“ The largest known study of twins with autism spectrum disorder (ASD) suggests that environmental influences and maternal infections during pregnancy may greatly increase risk for ASD.
Environmental influences include parental age, low birth weight and multiple births. The study suggested that both genetic and shared environmental factors significantly increase risk for ASD: an estimated 38 percent of risk being associated with genetic heritability and 58 percent with the environment that twins share during pregnancy and perhaps early infancy. The study also found that the relative contributions of shared genes and shared environment are similar for males and females."It has been well-established that genetic factors contribute to risk for autism," Clara Lajonchere, Ph.D., a study co-author and vice president of clinical programs for Autism Speaks, was quoted as saying. "We now have strong evidence that, on top of genetic heritability, a shared prenatal environment may have a greater than previously realized role in the development of autism."
The study involved 192 pairs of twins, both identical and non-identical, where at least one of the twins in the pair had autism. This approach allowed the researchers to look at how often both children in the twin pair received a diagnosis of autism. Study of identical twins, who share 100 percent of their genes, helps researchers determine the degree to which a disorder is inherited, or genetic; and comparison to fraternal twins, who share around 50 percent of their DNA, allows researchers to understand how environmental influences add to the risk of ASD.
The study could not pinpoint the specific time period (i.e. early pregnancy, late pregnancy or birth), nor the specific risk factors that contribute to the increased risk notes Dr. Lajonchere. "Indeed, multiple-birth pregnancies are themselves associated with increased risk of developmental disorders such as cerebral palsy and autism. This speaks to the importance of further study on what prenatal and perinatal factors increase risk beyond that of inherited genes."
SOURCE: Archives of General Psychiatry, published online July 4, 2011