Risk of Parkinson Disease in Individuals With Autism Spectrum Disorder.

Importance Recent research suggests a plausible biological link between autism spectrum disorder (ASD) and Parkinson disease (PD). Nonetheless, large longitudinal studies examining the risk of PD following ASD are lacking. Objective To examine the association between ASD and future PD risk. Design, Setting, and Participants A nationwide population-based prospective cohort study was performed using data from Swedish national registers. All individuals born in Sweden from 1974 to 1999 with follow-up from age 20 years until December 31, 2022, and with complete covariate data were included. The analysis was completed in August 2024. Exposures Diagnoses of ASD as a time-varying exposure obtained from the National Patient Register. Main Outcomes and Measures Diagnoses of PD were obtained from the National Patient Register through 2022. The relative risk (RR) of PD was quantified using incidence rate ratios with 95% CIs from Poisson regression. Preterm birth, depression, antidepressant use, and antipsychotic exposure over time were potentially modifying life events. Results The study included 2 278 565 individuals (median [IQR] age at exit, 34 [29-42] years; 1 106 772 female [48.6%]), contributing 33 858 476 person-years. PD occurred in 438 of 2 226 611 individuals without ASD (0.02%; 1.3 cases/100 000 person-years) and 24 of 51 954 individuals with ASD (0.05%; 3.9 cases/100 000 person-years) (RR, 4.43 [95% CI, 2.92-6.72]). The risk estimates were similar after adjusting for sex, socioeconomic status, family history of mental illness, family history of PD, and age at ASD diagnosis. Preterm or early-term birth was not associated with and did not modify the PD risk. Depression and antidepressant use (present in 24 257 individuals with ASD [46.7%]) were associated with increased risk of PD (RR, 2.01 [95% CI, 1.40-2.88]), independent of ASD. Antipsychotic exposure (present in 16 387 individuals with ASD [31.5%]) reduced but did not fully attenuate the association (RR, 2.00 [95% CI, 1.27-3.14]) and showed no interaction with ASD on PD risk. Conclusions and Relevance ASD was associated with increased risk of PD, even after adjusting for depression or antidepressant use and antipsychotic exposure. These findings suggest a potential shared etiology between neurodevelopmental disorders and PD, and a heightened awareness of long-term neurological conditions in individuals with ASD may be warranted.