Are your kids close in age? They may be at risk for autism

Are your kids close in age? If so, a new study suggests that your younger children may be at higher risk for developing autism.

The study, published in the January edition of the medical journal Pediatrics, links closely spaced pregnancies with an increase in autism diagnoses. Kids conceived before their older sibling was a year old were three times more likely to be diagnosed with some form of autism than children who were spaced at least three years apart, the study found.

Columbia University researcher Keely Cheslack-Postava, Ph.D., says that she and her colleagues did not look into the specific reasons for the uptick, but suspects that the mothers' bodies may not have had enough time between pregnancies to build up reserves of folate and iron, both of which are important in fetal development.

Though no one knows exactly what causes autism, many medical experts agree that the disorder is likely caused or at least influenced by a range of factors, including genetics and environment. In spite of the fact that vaccine-autism link has been debunked and Mercury-laced thimerosal has been removed from most vaccines, that debate still rages on, with some parents and researchers pointing to a "toxic tipping point" that triggers certain symptoms. This latest study shows that the prenatal environment may also play a part in the disorder.

The study looked at 662,730 second-born children in California between 1992 and 2002. "Even after adjusting for factors such as a mother's age, race, and education levels the findings still held," CNN reported. The rates also were not affected by premature birth or low birth rates.

But when it comes to autism, California has some unique factors of its own. The number of autism cases handled by that state's department of developmental service increased 636 percent from 1987 to 2003, according to an April 2010 Science Daily report. And two studies by researchers from the Institute for Social and Economic Research and Policy at Columbia University last year point to two possible reasons: localized environmental toxins and proximity to other children with autism.

In the first study, published in the Health & Place Journal, researchers analyzed data from 11,683 autistic children born in California between 1993 and 2001 and identified nearly 40 "clusters" in and around Los Angeles where high numbers of children with autism were found. In the largest of these, a 12-by-30-mile swath near West Hollywood, children were four times more likely to have been diagnosed with autism than elsewhere in the state. The second study, published in The American Journal of Sociology" and involving more than 300,000 California children, found that children who live near a child who has already been diagnosed with autism were more likely to receive an autism diagnosis themselves.

No, autism isn't contagious. But exposure to toxins in a particular area could explain the clusters, and an increase in autism awareness plus a decrease in the stigma associated with having autism could explain why more parents are willing to seek out a diagnosis. The autism spectrum itself has grown to include several disorders, including the all-encompassing PDD-NOS (Pervasive Developmental Disorder Not Otherwise Specified) that wouldn't have been considered to be autism just a decade or so ago.

And, of course, if you're already familiar with autism—the U.S. Department of Health and Human Services reports that about 1 in 100 children have an Autism Spectrum Disorder—then you know what to look for. According to the Columbia University researchers: "Meeting children with autism and having discussions with parents of children with autism could lead parents (of children not diagnosed with autism) to observe behavioral symptoms consistent with autism, to learn how to effectively identify and reach a physician, and to learn how to access and subsequently navigate services and service agencies."

So, should you change your pregnancy plans? Researchers say it's too early to tell, and that makes sense to us. The Duggar family, with 19 kids in 23 years and no autism diagnoses so far, does seem to defy the odds.

Also on Shine: