“This indicates that there can be shared biological drivers behind ASD and Parkinson’s disease,” says the study’s first author, Weiyao Yin, a researcher at the Department of Medical Epidemiology and Biostatistics, Karolinska Institute. “One hypothesis is that the brain’s dopamine system is affected in both cases, since the neurotransmitter dopamine plays an important part in social behaviour and motion control.”

It is well known that dopamine-producing neurons are degraded in Parkinson’s disease. Previous studies have also shown that dopamine is possibly implicated in autism, but more research needs to be done to confirm this.

“We hope that our results will eventually help to bring greater clarity to the underlying causes of both ASD and Parkinson’s disease,” says Dr Yin.

Medical checkups are vital

Depression and the use of antidepressants are common in people with autism, as are antipsychotic drugs, which are known for being able to cause Parkinson like symptoms. When the researchers adjusted for these factors, the correlation between ASD and the later development of Parkinson’s disease was less salient, but the risk was still double.

The researchers point out that they only analysed early-onset Parkinson’s disease before the age of 50 and that the average age of participants by the end of the study was 34. The incidence of Parkinson’s disease was therefore very low. Future studies will need to examine if the elevated risk persists into older age.