By Kathleen Doheny
TUESDAY, June 24, 2014 (HealthDay News) -- A mother's birthplace may affect her children's risk of developing an autism spectrum disorder, according to new research.
Children of foreign-born black, Central and South American, Filipino and Vietnamese mothers were more likely to have an autism spectrum disorder (ASD) compared to children born to white mothers who were born in the United States, the study found.
"The rates [of ASDs] in the African immigrants was the highest," said lead researcher Dr. Beate Ritz, chair of epidemiology at the Fielding School of Public Health at the University of California, Los Angeles.
The study also found that U.S.-born African American and Hispanic mothers, as well as foreign-born black and Central/South American mothers, were more likely to have children with a type of autism that included severe emotional outbursts and expressive language impairment, compared to U.S.-born white mothers.
The study is published in the July print issue of Pediatrics.
Although this study found an association between a mother's birthplace or race and the development of an autism spectrum disorder, the study doesn't show that these factors cause autism.
Autism spectrum disorders describe a range of developmental disabilities that can cause social, communication and behavioral difficulties. About 1 in 68 U.S. children have an autism spectrum disorder, the U.S. Centers for Disease Control and Prevention (CDC) estimates.
The exact cause of autism is unknown, but a number of risk factors have been found, including genetic risk factors, being born to older parents and having a sibling with the disorder, according to the CDC.
Previous studies have found autism spectrum disorders are most common among white children, Ritz noted.
In her study, Ritz wanted to look at the influence of the mother's race, ethnicity and birthplace. She and her colleagues reviewed the records of 7,540 children with autism who were born in Los Angeles County during the years 1998 to 2009 and given an autism diagnosis at ages 3 to 5 years. The researchers adjusted for other factors such as maternal age and education.
Compared to white children of U.S.-born mothers, the risk of autism was 76 percent higher for children of foreign-born black mothers, she said.
Mothers born in Vietnam, the Philippines, Central and South America also were at higher risk of having a baby with autism.
The researchers also found a small subgroup of 806 children who had both an autism spectrum disorder and mental retardation. For this group, having a foreign-born mother further increased the risk of the disorder. In fact, the risk was doubled for children born to foreign-born black mothers or those from the Philippines or Vietnam compared to U.S.-born white mothers, the study reported.
Additionally, for a specific type of the disorder that included severe emotional outbursts and impaired expressive language, U.S.-born Hispanic and black mothers, and foreign-born black and Central/South American mothers were more likely to have a child with this type of autism than U.S.-born white mothers.
The study wasn't designed to tease out the reasons behind this association, but Ritz has some theories. She believes that it's possible that "a child is more likely to develop an ASD if the mother emigrated from a country which had political unrest or wars in the recent past."
Even if those events were 20 or 30 years ago, it could still have an effect, she said. The mother giving birth may have witnessed atrocities of war or other trauma as a child, perhaps programming her to react to stress in a certain way. These mothers may react to stress in a certain way when pregnant, and that could affect the baby's ''brain wiring," she speculated.
As for whether these mothers can obtain ideal care and a prompt diagnosis for an autism spectrum disorder, Ritz cannot say, as it was outside the scope of the study. However, the average age at diagnosis for all the youngsters in this study was in the child's third year, according to the study.
"It's an interesting study to have done. It's a first step to begin to try in a more detailed fashion to identify other causes of autism," said Dr. Trevor Resnick, chief of neurology at Miami Children's Hospital. Resnick was not involved in the research, but reviewed the study's findings.
Pinning down the cause of autism spectrum disorders is complex, he said. Experts know genetic, metabolic and structural factors affect risk. "We know there is not one cause, there are multiple causes," he said.
There may even be multiple causes within one child, Resnick noted.
What the new study seems to identify is the risk of autism in different ethnic groups, he said. But the common factor is the immigrant status, not the ethnicity itself, he noted.