Can where a mother was born and raised be a risk factor for autism in her child? According to new research out of UCLA, the answer is: yes.
While the prevalence of autism has been reported to be highest among non-Hispanic white children, a new study from the UCLA Fielding School of Public Health has turned that notion upside down. Using data from the county of Los Angeles, California, a racially diverse region with a high percentage of recent immigrants, the researchers found that maternal nativity is a risk factor for childhood autism in U.S. populations. Specifically, they found that when compared with children born to white U.S. mothers, children of foreign-born black, Central/South American, Filipino, and Vietnamese mothers, along with U.S.-born African Americans and Hispanics, had a higher risk of autism.
For two decades, the authors report, autism prevalence has risen in the United States, now reaching 147 per 10,000 children who have been diagnosed with autism spectrum disorders (ASDs) by the age of eight, and 21 per 10,000 children with autistic disorder (AD).
According to Autism Speaks, an advocacy group, autism spectrum disorder and autism are both general terms for a group of complex disorders of brain development. These disorders are characterized, in varying degrees, by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviors.
Autism can be associated with intellectual disability, difficulties in motor coordination and attention and physical health issues such as sleep and gastrointestinal disturbances.
Until now, though, except for parental age and some pregnancy complications, evidence has been insuffcient for many of the potential prenatal risk factors for ASD. Since some recent European research has reported associations between immigration status of the mother and ASD, the researchers saw an opportunity.
“Epidemiology has a long tradition of using migration studies to understand how environmental and genetic factors contribute to disease risk in populations,” said senior author Beate Ritz, professor and chair of the department of epidemiology in the Fielding School.
The fact that 22 percent of six year olds’ born in the United States have immigrant parents opened a unique opportunity for us to consider the inffuence of nativity, race and ethnicity on the causes of ASD.
In the study, children born in Los Angeles County who had been diagnosed with autism between the ages of three to five during 1998–2009 were identified and linked to their California birth certificates. The birth certiffcates had information on the mother’s race, ethnicity, and where the mother was born. In total, 7,540 children with autism were identified from 1,626,354 births.
U.S. born African Americans and Hispanics, previously thought to have lower rates of autism, were found to have higher rates of ASD than whites, when the researchers looked at such factors as maternal race/ethnicity subgroups by nativity, and took into account such well-known risk factors as maternal age, maternal education, and insurance status. The latter are indicators for socio-economic conditions which are important since diagnosis may be related to health care access, she noted.
The reasons why maternal nativity outside of the U.S. is a risk factor for childhood autism in U.S. populations are quite varied, the study suggests. Voluntary migration involves physical relocation and is often preceded by uncertainty, with refugees sometimes facing life-threatening situations; said Ritz. After arriving, immigrants may end up in low-income neighborhoods, becoming socially vulnerable. Women from Central American nations (Guatemala, El Salvador) who migrated seeking asylum in the 1980s may have a history of trauma from civil war, violence, and displacement. Maternal life event stresses and psychiatric disorders, possibly related to experiences of escaping wars and disasters, as well as nutritional deffciencies from famine, may be possible explanations for the increased risks observed in Central American, Vietnamese, and some African immigrant groups.
“Language and cultural barriers, and a lack of access to health care could also have caused an under-estimate of ASD in these populations,” said Ritz, who is also a professor of Neurology and a member of the UCLA Brain Research Institute. She noted that these barriers are challenges for all children from all minority groups who were at higher risk compared with U.S.-born white children.
Finding that maternal nativity is a risk factor for childhood autism has important clinical implications as well, said Ritz. “Our findings suggest we need to do a better job of early identification and treatment of ASJ for these large and diverse immigrant communities who vary in risk, protective factors and access to health care,” she said.
-This information provided courtesy of UCLA Fielding School of Public Health
Other researchers on the study included first author Tracy Ann Becerra, Ondine S. von Ehrenstein, Julia E. Heck, Jorn Olsen, Onyebuchi A. Arah, Shafali Jeste, and Michael Rodriguez, all of UCLA. Funding for the study was provided by the UCLA Graduate Division and the UCLA California Center for Population Research, and supported by an infrastructure grant (R24HD041022) from the Eunice Kennedy Shriver National Institute of Child Health and Human Development.