THE PREVALENCE OF INTELLECTUAL DISABILITY AMONG CHILDREN UNDERGOING STANDARDIZED EVALUATION FOR ASD

Background: There has been recent debate over the number of individuals with autism spectrum disorders (ASD) who also meet criteria for mental retardation (MR)—now referred to as intellectual disability (ID). Recent, limited data suggest that the prevalence of ID in ASD ranges between 25.8% and 58.5%, with co-occurrence in 66% to 70% of children who meet strict criteria for autism. Yet these estimates can be quite discrepant depending on the stringency of diagnostic criteria, child age, and informant. 

Objectives: To determine the prevalence of ID among a large sample of children who underwent standardized evaluation for suspected ASD.

Methods: Data were pooled from the medical records of children who had received a research-reliable ADI-R and ADOS and a developmentally appropriate IQ test as part of their evaluation for possible ASD at Texas Children’s Hospital through December 31, 2007. The prevalence of ID, as defined by IQ scores of ≤ 70, was calculated by diagnosis (autism, ASD, neither).

Results: To date, complete data have been pooled for 192 children (84.3% male). Of these, 146 (76.0%) met strict criteria for autism, 4 (2.1%) met criteria for an ASD, and 42 (21.9%) did not meet criteria for either. The overall prevalence of ID was 59.9%; however, this differed significantly by diagnosis (Fisher’s exact = 22.03, df = 2, p < .0001), with rates of 68.5%, 75%, and 28.6% for the autism, ASD, and neither autism/ASD groups, respectively.

Conclusions: The ID prevalence was comparable to that in the literature for strict autism but higher for the ASD group, which could be attributed to the small number with this diagnosis. Data collection and analyses, including ID by child age at evaluation (≤ 5 years, 5 years +), are ongoing, with an anticipated final sample of approximately 400 children.