Objective

Growing awareness that symptoms of autism spectrum disorder (ASD) transcend multiple diagnostic categories, and major advances in the identification of genetic syndromes associated with ASD, have led to widespread use of ASD symptom measures in etiologic studies of neurodevelopmental disorders. Insufficient consideration of potentially confounding factors such as cognitive ability or behavior problems can have important negative consequences in interpretation of findings, including erroneous estimation of associations between ASD and etiologic factors.

Method

Participants were 388 children 2 to 13 years old with diagnoses of ASD or another neurodevelopmental disorder without ASD. Receiver operating characteristics methods were used to assess the influence of IQ and emotional and behavioral problems on the discriminative ability of 3 widely used ASD symptom measures: the Social Responsiveness Scale (SRS), the Autism Diagnostic Interview-Revised (ADI-R), and the Autism Diagnostic Observation Schedule (ADOS).

Results

IQ influenced the discriminative thresholds of the SRS and ADI-R, and emotional and behavioral problems affected the discriminative thresholds of the SRS, ADI-R, and ADOS. This resulted in low specificity of ASD cutoffs on the SRS and ADI-R for children with intellectual disability without ASD (27-42%) and low specificity across all 3 instruments for children without ASD with increased emotional and behavioral problems (36-59%). Adjustment for these characteristics resulted in improved discriminative ability for all of the ASD measures.

Conclusion

The findings indicate that scores on ASD symptom measures reflect far more than ASD symptoms. Valid interpretation of scores on these measures requires steps to account for the influences of IQ and emotional and behavioral problems.

Using questionnaires in research relies on the expectation that they measure the same things across different groups of individuals. If this is not true, then interpretations of results can be misleading when researchers compare responses across different groups of individuals or use in it a group that differs from that in which the questionnaire was developed. For the questionnaire we investigated, the Social Communication Questionnaire (SCQ), we found that parents of boys and girls responded to questionnaire items in largely the same way but that the SCQ measured traits and behaviors slightly differently depending on whether the children had autism. Based on these results, we concluded that researchers using this questionnaire should carefully consider these differences when deciding how to interpret findings. SCQ scores as a reflection of autism-associated traits in samples that are mostly or entirely made up of individuals without an autism diagnosis may be misleading and we encourage a more precise interpretation of scores as a broader indication of social-communicative and behavioral traits.

Background

Delayed walking is common in intellectual disability (ID) but may be less common when ID occurs with autism spectrum disorder (ASD). Previous studies examining this were limited by reliance on clinical samples and exclusion of children with severe motor deficits.

Objective

To examine in a population-based sample if age of walking is differentially related to intellectual ability in children with ASD versus other neurodevelopmental disorders (NDD).

Methods

Participants were from the nested Autism Birth Cohort Study of the Norwegian Mother, Father and Child Cohort Study (MoBa). Cox proportional hazards regression assessed if diagnosis (ASD n = 212 vs. NDD n = 354), continuous nonverbal IQ, and their interaction, were associated with continuous age of walking.

Results

The relationship between nonverbal IQ and age of walking was stronger for NDD than for ASD (Group × nonverbal IQ interaction, χ²  = 13.93, p = .0002). This interaction was characterized by a 21% decrease in the likelihood of walking onset at any given time during the observation period per 10-point decrease in nonverbal IQ (hazard ratio = 0.79, 95% CI: 0.78-0.85) in the NDD group compared to 8% (hazard ratio = 0.92, 95% CI: 0.86-0.98) in the ASD group.

Conclusions

The finding that age of walking is less strongly related to low intellectual ability in children with ASD than in children without other NDDs supports the hypothesis that ID in ASD may result from heterogeneous developmental pathways. Late walking may be a useful stratification variable in etiological research focused on ASD and other NDDs.

The parental report-based Autism Diagnostic Interview-Revised (ADI-R) and the clinician observation-based Autism Diagnostic Observation Schedule (ADOS) have been validated primarily in U.S. clinics specialized in autism spectrum disorder (ASD), in which most children are referred by their parents because of ASD concern. This study assessed diagnostic agreement of the ADOS-2 and ADI-R toddler algorithms in a more broadly based sample of 679 toddlers (age 35-47 months) from the Norwegian Mother and Child Cohort. We also examined whether parental concern about ASD influenced instrument performance, comparing toddlers identified based on parental ASD concern (n = 48) and parent-reported signs of developmental problems (screening) without a specific concern about ASD (n = 400). The ADOS cutoffs showed consistently well-balanced sensitivity and specificity. The ADI-R cutoffs demonstrated good specificity, but reduced sensitivity, missing 43% of toddlers whose parents were not specifically concerned about ASD. The ADI-R and ADOS dimensional scores agreed well with clinical diagnoses (area under the curve ≥ 0.85), contributing additively to their prediction. On the ADI-R, different cutoffs were needed according to presence or absence of parental ASD concern, in order to achieve comparable balance of sensitivity and specificity. These results highlight the importance of taking parental concern about ASD into account when interpreting scores from parental report-based instruments such as the ADI-R. While the ADOS cutoffs performed consistently well, the additive contributions of ADI-R and ADOS scores to the prediction of ASD diagnosis underscore the value of combining instruments based on parent accounts and clinician observation in evaluation of ASD. Autism Res 2017, 10: 1672-1686. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.