Social and Communication Subtypes in Autism Spectrum Disorders (ASD) without Intellectual Disability (ID)

Background:  Individuals with ASD without ID have been understudied relative to their lower functioning counterparts even though they comprise a large proportion of those with ASD. Social and communication symptoms are particularly valuable areas of study within this population as previous research has established impairments in these areas predict functioning across multiple domains. While individuals with higher functioning ASD manifest social/communication symptoms heterogeneously, prior research using person-centered approaches (e.g., latent class analysis [LCA], cluster analysis) has demonstrated homogenous subgroups exist within this context of variability, and can be been used to predict diagnostic presentation and language development. Previous work utilizing these approaches indicates derived classes differ on age, intellectual functioning, adaptive functioning, and ASD symptomatology, though these studies were primarily done in samples with ID and/or language impairment. The present study uniquely contributes to the literature by examining social/communication impairments in a sample with ASD without ID.

Objectives:  Employ an exploratory approach by using LCA to examine subtypes of social/communication symptoms in a sample with ASD without ID. Determine the variables on which derived classes differ from one another.

Methods:  Participants included 367 individuals (307 males, 60 females) with ASD without ID who were verbally fluent and ranged in age from 4-28 years. Scores from 20 overlapping items in Modules 3 and 4 of the Communication and Reciprocal Social Interaction sections of the Autism Diagnostic Observation Schedule (ADOS) were used in an LCA; derived subgroups were compared on ASD symptomatology, demographic variables, intellectual functioning, and adaptive functioning.

Results:  A three-class solution fit the data well and was conceptually meaningful. Classes 1, 2, and 3 comprised 43%, 29%, and 28% of the study sample, respectively. Classes significantly differed on ASD symptomatology, age F(2,361)=12.40,p<.001, full scale IQ F(2,359)=10.37,p<.001, verbal IQ F(2,317)=14.41,p<.001, and aspects of adaptive functioning (e.g., Daily Living Skills) F(2,266)=7.41,p=.001.

Conclusions:  These findings indicate social/communication impairments are meaningful variables to differentiate subtypes amongst a sample with ASD without ID. They support previous research documenting considerable social/communication impairment in the context of intact intellectual functioning. Between class comparisons on variables of interest indicate overall and verbal IQ have a protective effect for some aspects of the ASD phenotype (e.g.,structural language skills) but do not protect against symptoms that are multiply determined and involve core social problem solving. Comparison of age and ASD symptomatology across classes suggests abatement of social symptoms may occur up until a certain point (i.e.,adolescence) but the rate of symptom decline decreases thereafter. Adaptive functioning (daily living skills), was strongest in the class that demonstrated the fewest language–related symptoms, a finding that supports previous work relating language skills to adaptive skill development. These findings underscore the need for more intensive social skills’ intervention to promote better social outcomes and more externally valid measures of ASD symptomatology. Limitations of the current study include use of a cross-sectional design and future directions should attempt to examine longitudinal changes in social and communication symptoms across classes.