Elevated autistic features in Parkinson's disease and other motor disorders

Biological accounts have suggested an overlap between Parkinson's disease and autism despite their being studied largely at opposite ends of the life course. Characterising this overlap can identify potentially shared aetiologies and care pathways for these conditions. However, this overlap has so far only been tested in older autistic adults who show greater Parkinson's disease traits. The converse has not been directly assayed, that is, if adults with Parkinson's disease have higher autistic features. This preregistered study addressed this gap in the literature by asking whether adults with Parkinson's disease manifest elevated autistic traits. To test whether any such overlap might be unique to Parkinson's disease, we included two control groups: (1) people without any parkinsonism but with motor disability of neurological or neurovascular origin (other motor disorders), and (2) typically ageing controls with no motor disorders. We tested N = 330 participants (equal numbers of Parkinson's disease, other motor disorders and typically ageing controls) on their autistic traits and cognitive abilities. Clinical diagnoses were verified through a tertiary neurology clinic. Higher autistic traits were noted in both Parkinson's disease and other motor disorder groups compared to the typically ageing controls, suggesting an association between motor disorders and dimensional autistic traits. Exploratory analyses revealed a clear pattern of results in males, where Parkinson's disease was associated with the highest autistic traits, followed by the other motor disorders, and then by the typically ageing group. No such pattern was observed in females. These results are not explained by differences in language or age or reporter effects. This new evidence suggests a sex-specific overlap between these conditions and highlights the need for accounting for elevated autistic features in planning support for males with Parkinson's disease and other movement disorders.Lay AbstractPeople with autism are three times more likely than non-autistic people to develop Parkinson's disease in later life, and some of the same genetic variants contribute to risks for both these conditions. Although Parkinson's disease is more common in people with autism, is autism correspondingly more common in people with Parkinson's disease? Or what about autistic patterns of thought and behaviour, even in Parkinson's patients who are not also diagnosed, or diagnosable, with autism itself? We surveyed such autistic traits in three groups of older people: Parkinson's patients, patients with other neurological disorders of movement and those without any neurological or movement disorder or condition. Men with Parkinson's disease and men with non-parkinsonian motor disorders had more autistic traits than normal. Women with Parkinson's or other motor disorders, on the other hand, did not differ from women without any motor disorder. This was true no matter in which of the three languages surveys were given, and no matter whether it was patients themselves or their caregivers who completed the survey. Some underlying genetic or other biological shared factors might increase autistic traits not only in Parkinson's disease but also in some of the other motor disorders represented in this study's comparison group, for example, essential tremor. Conversely, Parkinson's disease might not be the only motor disorder to which people with autism stand at heightened risk. Assessment of autistic traits should be considered as part of care planning for people with Parkinson's disease or other motor disorders.