The differential diagnostic utility of the social communication questionnaire in mild intellectual disability and autism spectrum disorder: a case control study

Objectives: This study investigated the utility of specific predictive and discriminative items within the Social Communication Questionnaire (SCQ) for distinguishing between autism spectrum disorder (ASD), intellectual disability (ID), and co-occurring ASD + ID in children. Methods: A total of 137 children aged 4 to 12 years (52 typically developing (TD), 34 ASD, 26 ID, 25 ASD + ID) were included in the study. Cognitive development assessments were conducted for the ASD, ID, and ASD + ID groups in suitable cases. SCQ items were evaluated both in terms of total and subscale scores and individual items across groups. Results: The TD group had the lowest scores on the SCQ, while the ID group had significantly lower total and communication subscale scores on the SCQ compared to the ASD group. Additionally, there were no significant differences in SCQ scores between the ASD group and the co-occurring ASD + ID group. The ID group had lower scores on both the communication subscale and the total SCQ compared to the co-occurring ASD + ID group. The Receiver Operating Characteristic (ROC) analysis of SCQ total scores for differentiating the ASD + ID group from the ID group revealed an AUC of 0.834 for the total score, with a cutoff of 16.50 (sensitivity: 76%, specificity: 80.8%). Logistic regression identified 29 significant predictors distinguishing ASD + ID from ID, with absence of ‘Group play’ (p = 0.003, OR = 4.010) being the most predictive being in the ASD + ID group. Among the top items in the ROC analysis for the ID and ASD + ID groups, ‘Friends (absence of close or best friends)’, ‘Range of facial expression (absence of normal facial expressions)’, and absence of ‘Head shaking to mean no’ were identified as the highest discriminative factors. Conclusions: This study highlights the potential of using the SCQ alongside clinical assessments to diagnose ASD in individuals with ID, emphasizing non-verbal communication, participation in group play, presence of close or best friends, and range of facial expression as key distinguishing factors. Further research with larger samples and comparisons of educational interventions based on these indicators is essential for developing tailored educational programs for the ASD + ID group.