"We hope that our results will eventually help to bring greater clarity to the underlying causes of both ASD and Parkinson's disease," said first author of the study, Weiyao Yin, researcher at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet in a press release.
For the study, researchers analyzed data from close to 2.3 million individuals from national registers in Sweden. Participants were born between 1974 and 1999, and follow-ups were included from age 20 years old until December 2022. In particular, the researchers paid attention to diagnoses of autism spectrum disorder and Parkinson's disease alongside potentially modifying life events, including preterm birth, depression, antidepressant use, and antipsychotic exposure.
Ultimately, they found that receiving an autism diagnosis was linked to a four times higher likelihood of developing Parkinson's disease. This association remained even after controlling for factors like socioeconomic status and genetic predisposition for mental illness or Parkinson's disease.
"This indicates that there can be shared biological drivers behind ASD and Parkinson's disease. 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," said Yin.
While preterm or early-term birth did not modify Parkinosn's risk, depression and antidepressant use were linked to a higher risk of Parkinson's independent of autism diagnosis. Meanwhile, exposure to antipsychotics reduced but did not fully attenuate the link.
The researchers noted that they only analyzed early-onset Parkinson's disease before age 50 and that the participants had an average age of 34 years old by the end of the study. Future studies may thus examine whether the higher risk persists into older age.
Sources: EurekAlert, JAMA Neurology