Comparison of Adulthood Outcomes in Autism Spectrum Disorder With and Without Regression: A Population‐Based Birth Cohort Study

The long-term outcomes of regression in autism spectrum disorder (ASD) remain unclear. Previous evidence suggests that autistic individuals with regression have poorer adulthood outcomes across various indices than those without regression. We compared two groups-those with and without regression in ASD-among 168 participants from a population-based birth cohort study. These individuals were born in northern Yokohama, Japan, between 1988 and 1996 and were diagnosed with ASD by age seven. Participants were classified into groups based on real-time records from a community-oriented mass screening system. This study focused on four outcomes: IQ at age five, IQ in adulthood, incidence of epilepsy, and composite social ability score. None of the outcomes showed significant differences between the two groups. The standardized effect size (where a positive value favors the non-regression group) was 0.06 (95% CI: -0.08 to 0.21) for the composite social ability score, -0.16 (95% CI: -0.55 to 0.22) for IQ at age five, and -0.15 (95% CI: -0.62 to 0.33) for IQ in adulthood. The risk ratio of epilepsy in the regression group compared to the non-regression group was 0.59 (95% CI: 0.22 to 1.5). No significant differences were observed in any of the four outcomes between autistic individuals with or without regression. The confidence intervals of the effect sizes indicate that the impact of regression on IQ and psychosocial adaptation in adulthood, if present, is likely to be small to intermediate.