In the first comprehensive study of autism prevalence using a total population sample, an international team of investigators from the U.S., South Korea, and Canada estimated the prevalence of autism spectrum disorders (ASD) in South Korea to be 2.64%, or approximately 1 in 38 children, and concluded that autism prevalence estimates worldwide may increase when this approach is used to identify children with ASD. “Prevalence of Autism Spectrum Disorder in a Total Population Sample,” published today online in the American Journal of Psychiatry reports on a study of all children (approximately 55,000) ages 7-12 years in a South Korean community, including those enrolled in special education and the disability registry, as well as all children enrolled in general education schools. Children were systematically assessed using multiple clinical evaluations.

The research by Young Shin Kim, M.D., M.S., M.P.H., Ph.D. of the Yale Child Study Center, and her collaborators Bennett L. Leventhal, M.D., Yun-Joo Koh, Ph.D., Eric Fombonne, M.D., Eugene Laska, Ph.D., Eun-Chung Lim, M.A., Keun-Ah Cheon, M.D., Ph.D., Soo-Jeong Kim, M.D., HyunKyung Lee, M.A., Dong-Ho Song, M.D. and Roy Richard Grinker, Ph.D. found more than two-thirds of ASD cases in the mainstream school population, unrecognized and untreated. “These findings suggest that ASD is under-diagnosed and under-reported and that rigorous screening and comprehensive population studies may be necessary to produce accurate ASD prevalence estimates,” stated Autism Speaks Chief Science Officer Geraldine Dawson, Ph.D. “Autism Speaks funded this study to support better detection, assessment and services and to encourage international autism research.”

According to Dr. Kim, experts disagree about the causes and significance of reported increases in ASD, partly because of variations in diagnostic criteria and incomplete epidemiologic studies that have limited the establishment of actual population-based rates.

“We were able to find more children with ASD and describe the full spectrum of ASD clinical characteristics,” said Dr. Kim. “Recent research reveals that part of the increase in reported ASD prevalence appears attributable to factors such as increased public awareness and broadening of diagnostic criteria. This study suggests that better case finding may actually account for an even larger increase. While the current project did not investigate potential risk factors in this particular population, the study does set the stage for ongoing work to examine genetic and environmental factors contributing to the risk of ASD.”

This study is further evidence that autism transcends cultural, geographic, and ethnic boundaries and that autism is a major global public health concern, not limited to the Western world. To date, there is no evidence of differences in the way ASD is expressed in children around the world; however it is possible that cultural factors may impact diagnostic practices and prevalence estimates. As a result, the South Korean study took a comprehensive approach to mitigate potential cultural bias. According to Dr. Grinker, a cultural anthropologist at George Washington University, “Parent and teacher focus groups were conducted to identify local beliefs that might influence symptom reporting and to address stigma and misunderstandings related to ASD. Further, clinical diagnoses were established by Korean diagnosticians with extensive clinical and research experience in both the U.S. and Korea and were validated by North American experts.”

The study does not suggest that Koreans have more autism than any other population in the world. What it does suggest is that autism is more common than previously thought and that, if researchers look carefully, especially in previously understudied, non-clinical populations, they may find more children with ASD. In addition to the South Korean study, Autism Speaks is supporting similar epidemiological research efforts in India, South Africa, Mexico, and Taiwan, including the translation and adaptation of the gold-standard diagnostic instruments into languages spoken by more than 1.7 billion people worldwide.

“This is the first comprehensive population sample-based prevalence calculation in Korea, and replication in other populations is essential,” explained Dr. Dawson. “Notwithstanding the need for replication, this study provides important evidence that the application of validated, reliable and commonly accepted screening procedures and diagnostic criteria applied to a total population has the potential to yield an ASD prevalence exceeding previous estimates.”