Study: Low Birth Weight Linked to Autism Risk

A study involving twins at Northwestern University analyzed the possible environmental factors contributing to autism spectral disorder (ASD). In identical twins in which one twin had the disorder and the other did not, a lower birth weight more than tripled the risk of ASD.

Researchers already know a good deal about the genetic factors that contribute to ASD, but what’s unclear is how much of the ASD equation is controlled by genes and how much is controlled by environmental factors. So looking at identical twins, who have identical DNA, researchers can better isolate environmental factors and understand how they come into play.

The study included a population-based sample of 3,715 same-sex twins. The discordant twins (sets of twins where only one had the disorder) studied were ones where one twin weighed at least 14 ounces more than the other. Genetic and environmental factors were controlled in the study with a co-twin research design where the twin with ASD served as the case and the unaffected twin served as the control. The numbers? ASD risk increased 13 percent for every 3.5 ounce-decrease in birth weight.

“Because autism is a developmental disorder impacting brain development early on, it suggests that prenatal and perinatal environmental factors may be of particular importance,” said Molly Losh, researcher at Northwestern University and lead author of the study, in a press statement.

A caveat, Losh points out, is that this research may not be applicable to single births. There are key differences between the prenatal and perinatal conditions in singletons and twins.

There have been many theories—including lots of misguided ones—about the cause of autism. In the 1950s the “refrigerator mom” theory suggested that the mother’s emotional indifference—or frigidity, if you will—was to blame for a child’s ASD. Now we have the hotly contested belief that vaccines cause autism; the medical community largely debunks it but may parents are still worried. While no solid answer yet pinpoints what causes ASD, a disorder affecting approximately one in every one hundred children, I think we can all agree that research has come a long way since the dark days of the “refrigerator mom.”