The prevalence rate of Autism Spectrum Disorders (ASD) appears to be steadily increasing. The latest report from the Center for Disease Control estimates the rate of ASD is 1 in 91 children (Kogan, 2009), up from 1 in 150 in 2007. Understanding the seeming changes in ASD prevalence require careful exploration of genetic and environmental factors. A method that has proven useful in dissecting the etiology of complex diseases is the study of isolated populations. One population isolate that has been studied extensively is the Amish, with well over 250 genetic studies. Expanding studies of autism to the Amish may provide important information about etiology. A crucial first step in this process is a feasibility study to determine ASD prevalence rates in this population.
This study presents preliminary data on the estimated prevalence of ASD among the Amish in two Amish dominant counties as part of a larger epidemiological study. All children between ages 3 to 21 in those counties will be screened for the presence of an ASD.
Screening occurred in Holmes County, Ohio and Elkhart-Lagrange County, Indiana, two of the largest Amish communities in the United States. Trained clinicians ascertained door to door using a published Amish Directory as a guide. Families were approached and asked to participate in a brief interview regarding their children. Two primary screening instruments were used: the Social Communication Questionnaire (SCQ) and the DSM-IV-TR Checklist (a tool created by the authors). A Vaccination History and a brief family history including questions specific to the ASD phenotype were also taken. Children screening positive on either the SCQ or DSM-IV-TR Checklist were seen for a more comprehensive clinical evaluation by two licensed psychologists. This evaluation included the Autism Diagnostic Observational Schedule (ADOS) and Autism Diagnostic Interview (ADI).
From September 2008 to October 2009, 1899 Amish children were screened in the two Amish communities. A total of 25 children screened positive for ASD on either the SCQ or the DSM-IV-TR checklist. A total of 14 screened positive for ASD on both screeners. Of those 25 children, 14 were evaluated and seven children were confirmed as having a diagnosis of ASD using the ADI and/or ADOS, and clinical judgment. Interestingly, four of the seven only met ASD criteria on the ADOS but not the ADI. Three of the four who were not diagnosed by the ADI only missed criteria on the Behavioral Domain, which may be attributable to the reporting style of Amish caregivers.
Preliminary data have identified the presence of ASD in the Amish community at a rate of approximately 1 in 271 children using standard ASD screening and diagnostic tools although some modifications may be in order. Further studies are underway to address the cultural norms and customs that may be playing a role in the reporting style of caregivers, as observed by the ADI. Accurate determination of the ASD phenotype in the Amish is a first step in the design of genetic studies of ASD in this population.