In the 1950s, medical opinion held that autism was caused by uncaring "refrigerator mothers." That perception was smashed in the 1970s by evidence that autism was probably tied to genetic factors. However, an MIT neuroscientist now believes that autism may in fact have an environmental component, albeit one that operates through genetic, and not social, behavior.

In work that focused on specific genes crucial to developing brains, the Picower Institute's Mriganka Sur, who also chairs MIT's brain and ­cognitive-sciences department, and Alvin W. Lyckman, a former MIT postdoctoral associate now at Tufts University, used DNA microarrays to pinpoint genes expressed during a critical period of brain development in mice. They found a set of calcium-­sensing genes that are particularly apt to switch their expression patterns in response to environmental influences. In humans as in mice, calcium activates signaling pathways that stimulate neuronal gene expression. Calcium deprivation could prevent some genes from being expressed; the resulting dearth of critical proteins could be one of the culprits behind autism.

"If we understood how genes changed in response to environmental influences in the developing brain, we might be able to one day prevent or reverse the changes," says Sur.