Short-term and Long-term Stability of the Autism Diagnostic Observation Schedule (ADOS-2) Calibrated Comparison Scores (CCS) and Classification Scores in Youth with Down Syndrome or Fragile X Syndrome with Intellectual Disability.

Researchers studied how consistent autism assessments are over time in children with Down syndrome or Fragile X syndrome. They found that autism test scores stayed fairly consistent, but autism diagnoses sometimes changed between visits, especially for children with Down syndrome. Children whose diagnoses changed tended to have milder autism symptoms and better language skills.

This longitudinal study examined the reliability of ADOS-2 autism assessments in 166 youth with Down syndrome (76 participants) or Fragile X syndrome (90 participants) who also had intellectual disability. Researchers assessed participants at three time points to evaluate short-term and long-term consistency of autism measures. While calibrated comparison scores showed good consistency over time in both groups, repetitive behavior scores were less reliable, particularly in Down syndrome. ASD classifications varied significantly over time, especially in the Down syndrome group.

Participants with variable classifications had lower autism severity scores and stronger language abilities compared to those with stable ASD classifications.

Results suggest ADOS-2 provides reliable severity measures but diagnostic classifications may vary over time, particularly in Down syndrome. Clinicians should consider language abilities and autism severity when interpreting assessments and making diagnostic decisions in these populations.

Study limitations include unclear methodology details, unknown sample size specifications, and lack of information about assessment intervals. The abstract does not provide details about participant demographics beyond age and gender distribution.

Autism diagnosis in individuals with fragile X syndrome (FXS) or Down syndrome (DS) with co-occurring intellectual disability is complex since clinicians often must consider other co-occurring behavioral features. Understanding how best to assess the features of autism in individuals with these conditions is crucial. In this study, we consider the short-term and long-term psychometric consistency of the Autism Diagnostic Observation Schedule-2 (ADOS-2) calibrated comparison scores (CCSs) and ASD classifications in individuals with FXS or DS. 76 individuals with DS (39 males; M = 15.27) and 90 individuals with FXS (71 males; M = 14.52 years) completed an assessment battery (ADOS-2, abbreviated IQ assessment and semi-structured language sample) at three timepoints (initial visit, short-term stability visit, long-term stability visit). All CCSs were found to have short-and long-term consistency for both groups, with lowest reliability scores for the repetitive behaviors (RRB) CCSs.

Decreased reliability of RRB CCSs was found in the DS group than the FXS group. Variable short- and long-term ASD classifications were observed in both groups, with significantly higher variability in the DS group. Across groups, participants with variable classifications had lower ADOS-2 CCSs and higher language scores than those with stable ASD classifications. In the FXS group, those with variable classifications earned higher cognitive scores than did participants with stable ASD classifications.

These findings highlight the high incidence of autism symptomatology in individuals with DS or FXS and co-occurring intellectual disability, while elucidating the short- and long-term variability of symptom expression in the context of structured observational tasks such as the ADOS-2.