Age-related differences in behavioral and brain predictors of parkinsonism in autistic adults.

Autistic adults experience lifelong motor differences and may have increased vulnerability to parkinsonism, yet behavioral and neuroanatomical correlates of motor challenges across adulthood remain poorly understood. We examined cross-sectional behavioral and motor-related brain region morphology in autistic (n = 123) and non-autistic (n = 102) adults aged 18-71 years using the Parkinsonism Screening Questionnaire (PSQ), Adult Repetitive Behavior Questionnaire-2 (RBQ-2A), finger tapping, and MRI-derived cortical thickness and subcortical volumes of motor-related brain regions. Replication of the questionnaire analyses was conducted in an independent cohort of middle- and older-aged autistic adults from the Simons Powering Autism Research (SPARK; n = 210; ages 42-80 years), whereas structural MRI and finger tapping analyses were limited to the Arizona cohort. Autistic adults reported significantly higher PSQ scores than non-autistic adults. A significant group-by-age interaction was observed for RBQ-2A Factor 1, with autistic adults showing a steeper age-related reduction in repetitive motor and sensory behaviors. RBQ-2A scores were positively correlated with PSQ scores across both cohorts. Finger tapping performance did not differ between groups. Caudate volumes were larger in autistic adults and showed a modestly stronger negative association with age that did not survive multiple comparison correction. These findings suggest that self-reported restricted, repetitive motor behaviors and interests may serve as an indicator of self-reported parkinsonism-like symptoms in autism and highlight the need for longitudinal studies to clarify mechanisms of parkinsonism risk across the lifespan.