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Increasing numbers of children with known genetic conditions and/or intellectual disability are referred for evaluation of autism spectrum disorder (ASD), highlighting the need to refine autism symptom measures to facilitate differential diagnoses in children with cognitive and language impairments. Previous studies have reported decreased specificity of ASD screening and diagnostic measures in children with intellectual disability. However, little is known about how cognitive and language abilities impact the measurement of specific ASD symptoms in this group. We aggregated a large sample of young children (N = 1196; aged 31–119 months) to examine measurement invariance of ASD symptoms among minimally verbal children within the context of the Autism Diagnostic Observation Schedule (ADOS) Module 1. Using confirmatory factor analysis (CFA) and moderated non-linear factor analysis (MNLFA), we examined how discrete behaviors were differentially associated with the latent symptom domains of social communication impairments (SCI) and restricted and repetitive behaviors (RRB) across spoken language levels and non-verbal mental age groupings. While the two-factor structure of SCI and RRB held consistently across language and cognitive levels, only partial invariance was observed for both ASD symptom domains of SCI and RRB. Specifically, four out of the 15 SCI items and one out of the three RRB items examined showed differential item functioning between children with “Few to No Words” and those with “Some Words”; and one SCI item and one RRB item showed differential item functioning across non-verbal mental age groups. Moreover, even after adjusting for the differential item functioning to reduce measurement bias across groups, there were still differences in ASD symptom domain scores across spoken language levels. These findings further underscore the influence of spoken language level on measurement of ASD symptoms and the importance of measuring ASD symptoms within refined spoken language levels, even among those with minimal verbal abilities.

Profiles of scores on measures of intellectual functioning may aid in understanding etiology and developing targeted intervention in autism spectrum disorder (ASD) by providing details about specific phenotypes or subpopulations of ASD. Research investigating the relationship between ASD symptoms and intellectual functioning suggests that scores on the factors comprising global measures of intellectual functioning may be related to ASD symptoms (e.g., Joseph et al. J Child Psychol Psychiatry 43:807-821, 2002). Research has been limited by methodological problems, such as defining samples using unreliable subtypes of ASD and an overreliance on variable-centered methodological strategies. In the current paper, the authors provide a summary of existing research related to ASD symptoms and measures of intellectual functioning, review recent research identifying subpopulations in ASD, and provide goals for future areas of research in this area.

Autism spectrum disorder (ASD) diagnoses are made based on a pattern of behavioral symptoms, yet a growing body of research indicates that when, and indeed whether, an individual receives a diagnosis of ASD is influenced by myriad demographic factors including race, ethnicity, socioeconomic status (SES), and parental education level. The current manuscript provides a focused review of a subset of existing literature chosen to demonstrate how demographic factors may be related to the identification of individuals with ASD within the United States. Several possible explanations for existing disparities are discussed, along with clinical implications for professionals working with children from diverse backgrounds who are suspected of having ASD. Additional research in this area is needed to facilitate development of effective means to eliminate the diagnostic disparities.