Somali children were more likely to have the disorder than non-Somali black children or Hispanic children in the city, the study found. The study didn't explore why and didn't speculate on possible reasons. But the findings back up the common belief among Somalis in Minneapolis that their children suffer from high rates of the disorder, said Amy Hewitt, the lead researcher on the study.
"A lot of children in the city of Minneapolis, including Somali children, have autism spectrum disorder and many of them are getting diagnosed late," Hewitt said in an interview. "The average was five years. Kids can be reasonably diagnosed at age 2. So it's really important to get these kids and families connected to services."
According to the study, about 1 in 32 Somali children ages 7 to 9 were identified with autism spectrum disorder in Minneapolis in 2010, compared with 1 in 48 Minneapolis children overall, 1 in 62 non-Somali black children and 1 in 80 Hispanic children. The incidence was 1 in 36 white children, which the researchers said was not a statistically significant difference from the Somali figure.
Autism spectrum disorder refers to a group of developmental disabilities that includes autism and Asperger syndrome, affecting social interaction, communications and behaviour. Researchers say most cases appear to be caused by a combination of genetic risk factors and environmental stresses that influence early brain development.
Hewitt, along with officials from the Centers for Disease Control and Prevention and the advocacy group Autism Speaks, warned against comparing the new Minneapolis figures with a widely cited CDC estimate that 1 in 88 American children has autism spectrum disorder. The estimated national average is based on 2008 data.
Updated CDC estimates that are due out next spring, and will be based on 2010 data, are expected to show a higher national incidence partly because people are getting better at identifying the disorder, said Michael Rosanoff, Autism Speaks' associate director of public health research and scientific review.
The Minnesota researchers said they reviewed more than 5,000 clinical and school records, using established CDC statistical methods for estimating the prevalence of autism spectrum disorder in a community. The study looked only at data from Minneapolis, the centre of Minnesota's Somali community, which is the largest in the United States.
The study was funded by the CDC, the National Institutes of Health and Autism Speaks.
"This is the largest study of Somali children with autism in the United States. I think it is a very important study that gives us information we didn't have previously," said Marshalyn Yeargin-Allsopp, chief of the CDC's Developmental Disabilities Branch.
Another significant finding, Hewitt said, was that Somali children were far more likely to have an intellectual disability such as low IQ on top of their autism spectrum disorder than other children with it in Minneapolis.
"We don't know why. We just know there's a very significant difference in Somali children how ASD is manifesting itself," Hewitt said. "That's a really important future research question."
The findings came as long-awaited validation for Idil Abdull, co-founder of the Somali American Autism Foundation. She said she struggled for years to try to persuade officials there even was a problem. Abdull, who lives in Burnsville, said autism was essentially unknown in her native Somalia, but her 11-year-old autistic son barely speaks a word.
Federal and state agencies now need to find the cause and the cure, she said.
"Don't take another five years, CDC and NIH. You've got to come with your boots on and your hats on and do something about this, because these kids are as American as apple pie," she said.