Objectives: The objective of this analysis was to determine the prevalence of ASD in a population of 8-year-old children with intellectual disabilities.
Methods: Data were analyzed from an ongoing active, population-based surveillance program conducted in South Carolina as part of the Centers for Disease Control and Prevention’s Autism and Developmental Disabilities Monitoring Network. Prevalence data for ID and ASD among 8-year-old children from three points in time, 2002, 2004, and 2006 were analyzed for overall prevalence of ID and comorbid ASD, severity of ID and for the influences of gender and race/ethnicity. Chi-square analysis was used to determine significance of results.
Results: The prevalence of ID in this group of 8-year-old children was approximately 19 per 1000 or 1 in 53. Sixteen percent of children with ID had a comorbid diagnosis of ASD. For children with ID plus ASD, the overall prevalence was 3.1 per 1000 or 1 in 323. The prevalence ratio of males to females with ID plus ASD was 3.7 (p<0.05), and the prevalence ratio of blacks to whites was 1.5 (p<0.05). Among females with ID plus ASD, 66% were in the mild range, 22% in the moderate range, 10% in the severe range and 2% in the profound range. For males: 57% in the mild range, 26% in the moderate range, 12% in the severe range, and 3% in the profound range.
Conclusions: Results indicate that ASDs affect 16% of 8-year-old children with intellectual disabilities. A significant number of boys with ID have comorbid ASD suggesting that routine ASD screening may be appropriate in this population. Given the relative frequency of ASD among children with ID, tailored assessment and intervention approaches may be needed. These results emphasize the need for increased attention for a subgroup of the ID population having a comorbid diagnosis of ASD.