High rates of Parkinson's disease diagnosis in the autistic population: True co-occurrence or a product of overlapping traits?

Older autistic adult literature is sparse, and little is known about the aging autistic population. However, recent evidence suggests an increased prevalence of Parkinson's disease (PD) diagnosis in the autistic population. It may initially be assumed that autistic individuals are genetically more likely to develop PD, but extant genetic studies do not provide strong evidence for a link between the two conditions. An underappreciated body of evidence may shed light upon why autistic individuals score highly on PD diagnostic criteria: movement differences in autism have been likened to PD. Given that PD diagnosis is primarily movement-based, if it is the case that autistic movement appears parkinsonian, this may facilitate autistic individuals meeting diagnostic criteria for PD. If validated, this theory could have serious implications for the specificity of the PD diagnostic process. Here, we set out the evidence for high rates of PD diagnosis and parkinsonism in the autistic population and subsequently question why this might be the case, making reference to genetic and behavioural similarities between autism and PD.