Dr. Mohammad H. Rahbar
Dr. Mohammad H. Rahbar

Ongoing research by professors at McGovern Medical School and UTHealth could help answer questions regarding environmental factors and their influence on the etiology of autism spectrum disorder (ASD) in Jamaica.

Since 2009, Dr. Mohammad H. Rahbar, division director and professor of Clinical and Translational Sciences in the Department of Internal Medicine, has collaborated with faculty of the University of the West Indies (UWI) to examine the role of six metals, polychlorinated biphenyls, and organochlorine pesticides in ASD. Researches also studied interactions between environmental factors and three glutathione S-transferase genes (GSTM1, GSTP1, and GSTT1) that are involved in the detoxification of xenobiotics.

Although the causes of ASD are unknown, Rahbar said evidence suggests that gene-environment interaction is implicated in its pathogenesis. Some heavy metals are thought to be associated with ASD through mechanisms such as oxidative stress and Rahbar’s team chose Jamaica because the population is “thought to be at higher risk of exposure to these chemicals, particularly through the high consumption of seafood.”

Thus far, the research has yielded more than 10 publications, including the finding that the ages of parents are jointly associated with ASD in Jamaica. Previous studies inconsistently reported either the age of the mother or age of the father was a risk factor for ASD, so investigators included both ages of mother and father as independent variables in the regression models.

“However, since the ages of the parents are often highly correlated, including the ages of both parents in a regression model can lead to a statistical phenomenon called multicollinearity, which can obscure the true association,” Rahbar said. “By jointly modeling the age of the mother and father as a vector of outcome variables in a Multivariate General Linear Model, our findings indicate that the ages of both parents are jointly associated with ASD.”

Most recently, researchers found that maternal exposures to fever or infection, physical trauma, and oil-based paints during pregnancy or breastfeeding may be associated with ASD.

Rahbar’s team also found that Jamaican children aged 2 to 8 years old have higher mean blood levels of some of the six heavy metals.

“Specifically, the mean blood lead concentration is 2-3 times higher, the mercury concentration is 3 times higher, and the arsenic concentration is 4.5 times higher in Jamaican children compared to North American children,” Rahbar said. “In relation to ASD, we found significant interactions between manganese and GSTP1. Since neither manganese nor GSTP1 were independently associated with ASD, this association may have been missed if the joint effects of manganese and GSTP1 in relation to ASD were not explored.”

Rahbar said the group hopes to continue its collaboration with UWI to investigate the role of prenatal and postnatal exposure to the six metals in cognitive development and externalizing behavior in Jamaican children using data from a Jamaican birth cohort study initiated in 2011.

“In addition, we have established new relationships with collaborators in other countries, including Pakistan, and Romania, to initiate pilot projects investigating these and other chemicals suspected to be associated with ASD,” Rahbar said. “We hope to apply for funding for an international multi-center case-control study on ASD in the future.”