This study examines different ways of measuring the onset of symptoms in autism spectrum disorder (ASD). The present findings suggest that declining developmental skills, consistent with a regressive onset pattern, are common in children with ASD and may be more the rule than the exception. The results question the accuracy of widely used methods of measuring symptom onset and argue against their widespread use.

Studies of infants at risk for autism spectrum disorder (ASD) have proliferated, but few of these samples have been followed longer-term. We conducted a follow-up study, at age 5.5-9 years, of younger siblings of children with ASD (high-risk group, n=79) or typical development (low-risk group, n=60), originally recruited as infants. Children with ASD were excluded because of the focus on understanding the range of non-ASD outcomes among high-risk siblings. Using examiner ratings, parent ratings, and standardized assessments, we evaluated differences in clinical outcomes, psychopathology symptoms, autism symptoms, language skills, and nonverbal cognitive abilities. After adjusting for covariates, the high-risk group had increased odds of any clinically elevated/impaired score across measures relative to the low-risk group (43% vs. 12%, respectively). The high-risk group also had increased odds of examiner-rated Clinical Concerns (CC) outcomes (e.g., ADHD concerns, broader autism phenotype, speech-language difficulties, anxiety/mood problems, learning problems) relative to the low-risk group (38% vs. 13%, respectively). The high-risk group with CC outcomes had higher parent-reported psychopathology and autism symptoms, and lower directly-assessed language skills, than the Low-Risk Typically Developing (TD) and High-Risk TD groups, which did not differ. There were no differences in nonverbal cognitive skills. For some in the high-risk group, clinical concerns persisted from early childhood, whereas for others clinical concerns were first evident at school-age. Results suggest continued vulnerability in at least a subgroup of school-age children with a family history of ASD and suggest that this population may benefit from continued screening and monitoring into the school-age years.

Past events are often reported as occurring more recently than they actually took place, an error called forward telescoping. This study examined whether forward telescoping was evident in parent reports of ASD symptom emergence and onset classification. Parents were interviewed when their child was 2–3 years old (Time 1) and approximately 6 years old (Time 2). Significant forward telescoping was found in both age of social regression and age when language milestones were achieved, but not age of language regression. The correspondence between Time 1 and Time 2 onset report was low (kappa=.38). Approximately one-quarter of the sample changed onset categories, most often due to parents not recalling a regression at Time 2 that they had reported at Time 1. These results challenge the use of retrospective methods in determining onset patterns.