UC Davis

It is unclear how common is change in the severity of autism symptoms during childhood, whether symptoms change consistently across development, and what characterizes children that either increase or decrease in autism symptom severity during childhood. We evaluated these questions across three studies incorporating children from the University of California, Davis MIND Institute’s Autism Phenome Project and Girls with Autism imaging of Neurodevelopment cohorts. Autism symptoms and severity level were evaluated using the ADOS Calibrated Severity Score (CSS). Around half (46%-51%) of the children in the cohort changed in symptom severity level over time, with the other half remaining stable. Change in symptom severity was not consistent but rather fluctuated over time; severity decreases were more common during early childhood while severity increases occurred at both early and middle childhood. Most children experienced change during only one period and remained stable during the other. Social-communication challenges and restricted/repetitive behaviors (RRBs) changed differently across childhood. During middle childhood, increase in social-communication symptoms was especially prominent in parallel to RRBs severity decrease. Being female, having higher and increasing IQ, higher adaptive functioning, and having older, more educated parents were associated with decrease in symptom severity. Decreasing RRBs severity during middle childhood was associated with higher anxiety and probability for having an anxiety disorder at 11 years of age. Increasing symptom severity was associated with having lower and stable IQ, lower adaptive functioning and not making peer-equivalent gains over time, lower parental education level and younger parental age at the child’s birth. Increasing severity of social-communication challenges during middle childhood was associated with elevated and increasing anxiety, ADHD, disruptive behavior problems and overall psychopathology. Symptom severity change patterns were not associated with either initial severity level at 3-years-of-age or intervention history. We discuss findings in light of the literature and implications for defining autism severity level and suitable interventions.