Research by scientists at Albert Einstein College of Medicine of Yeshiva University may help explain how some cases of autismspectrum disorder (ASD) can result from environmental influences rather than gene mutations. The findings, published online inPLOS Genetics, shed light on why older mothers are at increased risk for having children with ASD and could pave the way for more research into the role of environment on ASD.
The U.S. Centers for Disease Control and Prevention announced in March that one in 68 U.S. children has an ASD - a 30 percent rise from 1 in 88 two years ago. A significant number of people with an ASD have gene mutations that are responsible for their condition. But a number of studies - particularly those involving identical twins, in which one twin has ASD and the other does not - show that not all ASD cases arise from mutations.
In fact, a major study of more than 14,000 children with ASDs published earlier this month in the Journal of the American Medical Association concluded that gene abnormalities could explain only half the risk for developing ASD. The other half of the risk was attributable to "nongenetic influences," meaning environmental factors that could include the conditions in the womb or a pregnant woman's stress level or diet.
Media reports on the causes of ASD have focused on the fact that older fathers (40 and over) are more likely than younger fathers to have children with an ASD, probably because of gene mutations that accumulate over the years in sperm-making cells. Yet older mothers (35 and over) face a similar risk that is entirely independent of their partners' age. But for older mothers, scientists know very little about why this risk exists. The Einstein researchers looked for genetic as well as environmental influences that might account for older mothers' increased risk for having children with ASD.
Their study, led by Esther Berko, an M.D./Ph.D. student in the lab of John Greally, M.B., B.Ch., Ph.D., involved 47 children with ASD and 48 typically developing (TD) children of women 35 and over. Unlike other ASD studies, this one included a significant number of minority children (Hispanic and African-American) from the Bronx. Brain cells - the obvious cells to examine for evidence of genetic and environmental differences between ASD and TD children - obviously could not be used. Instead, the researchers realized that if such differences existed, they should also occur in a readily available type of cell: the buccal epithelial cells that line the cheek.
"We hypothesized that whatever influences lead to ASD in children of older women probably are already present in the reproductive cells that produce the embryo or during the very earliest stages of embryonic development - in cells that give rise to both the buccal epithelium and the brain," said Dr. Greally, the study's senior author. "This would mean that whatever abnormalities we found in the cheek cells of children with an ASD versus TD children should exist in their brain cells as well." Dr. Greally is professor of genetics, of medicine and of pediatrics, director of the Center for Epigenomics and the Ruth L. and David S. Gottesman Faculty Scholar for Epigenomics at Einstein and attending physician, pediatrics at The Children's Hospital at Montefiore.