According to a new comprehensive study conducted in South Korea, the incidence of autism may be much higher than previously thought in the United States and elsewhere in the world. In the first study to take a broad-population look at the prevalence of autism spectrum disorders, types of autism ranging from severe symptoms to the milder Asperger's syndrome, researchers found a rate of 2.64% among South Korean children. That's 1 in 38 children, a rate far higher than the estimate of 1 in 110 children for the U.S. by the Centers for Disease Control and Prevention.
The study will be published in the American Journal of Psychiatry next Monday, and suggests that, under rigorous examination, many more children may be affected than previously suspected.
The five-year study, funded partly by Autism Speaks and led by Dr. Young-Shin Kim of the Yale Child Study Center, differed significantly in how it was carried out from earlier autism-prevalence studies. This most likely accounts for the dramatically different findings, Kim said. Previous studies assessing population-wide autism rates typically focused on high-risk populations, such as classrooms of special education students. In contrast, the new study conducted in South Korea assessed more than 55,000 children, ages 7 to 12, not only from special education classrooms and mental health service organizations but also regular schools.
Using several diagnostic techniques and measures to evaluate the children, the study found that the rates of autism spectrum disorder among the children in special education and mental health services programs were similar to estimates elsewhere in the world — from 0.6% to 1.8% of the population. But when students in regular schools were part of the assessment, the prevalence rate rose to 2.64%. Children in regular schools are more likely to be higher functioning and thus undiagnosed.
The study in South Korea found, for example, that many of the children diagnosed with autism spectrum disorder that were in regular schools "looked very different" from autistic students in special education classes, Kim said. Many had Asperger's syndrome, a milder form of the condition. These children tended to have normal intelligence but poor social skills. Kim said children in regular American classrooms should be included in future studies to get a better measure of the incidence of autism spectrum disorders. If that were done, she added, the prevalence of the condition in the U.S. and other countries also would be in the range of 2% to 3%.
South Korea has a well-established health and education system with a variety of cultures. This combination provided good criteria for the study.
The conclusions are more far-reaching, Dawson said. "This study clearly confirms that autism is a significant, global, public health concern that transcends cultural, ethnic and geographic boundaries," she said. "We do need to do this type of study in the U.S. … Until we do, we won't know what the population prevalence is."
Another recent study, conducted by the University of California- Davis School of Medicine, suggest that children conceived in winter seem to have a greater risk of being diagnosed with autism.
The investigators analyzed data from 6.6 million children who were born in California between January 1990 and December 2002 and followed up until the children were 6 years old. The risk of an autism diagnosis was higher for children conceived in December, January, February and March than for those conceived in other months of the year, the study found.
Compared with children conceived in July, the risk for autism was 8 percent higher among those conceived in December and 16 percent higher for those conceived in March, according to the report published online May 3 in Epidemiology.
Environmental factors, including exposure to seasonal viruses such as influenza and changes in diet, may play a role in the greater risk for autism among children conceived during the winter, according to the researchers.
"Studies of seasonal variations can provide clues about some of the underlying causes of autism," Irva Hertz-Picciotto, chief of the division of environmental and occupational health at the University of California-Davis School of Medicine, said in a university news release. "Based on this study, it may be fruitful to pursue exposures that show similar seasonal patterns, such as infections and mild nutritional deficiencies."
"However, it might be that conception is not the time of susceptibility," Hertz-Picciotto added. "Rather, it could, for instance, be an exposure in the third month of pregnancy, or the second trimester, that is harmful. If so, we might need to look for exposures occurring a few months after conceptions that are at higher risk -- for example, allergens that peak in the spring and early summer."
Autism–society.org offers information for parents who may think their child is exhibiting signs of Autism.
The characteristic behaviors of autism spectrum disorders may or may not be apparent in infancy (18 to 24 months), but usually become obvious during early childhood (24 months to 6 years).
As part of a well-baby/well-child visit, your child's doctor should do a "developmental screening," asking specific questions about your baby's progress. The National Institute of Child Health and Human Development (NICHD) lists five behaviors that signal further evaluation is warranted:
- Does not babble or coo by 12 months
- Does not gesture (point, wave, grasp) by 12 months
- Does not say single words by 16 months
- Does not say two-word phrases on his or her own by 24 months
- Has any loss of any language or social skill at any age
Having any of these five "red flags" does not mean your child has autism. But because the symptoms of the disorder vary so much, a child showing these behaviors should have further evaluations by a multidisciplinary team. This team may include a neurologist, psychologist, developmental pediatrician, speech/language therapist, learning consultant, or other professionals knowledgeable about autism.