🧠 Parkinson: the affected side predicts disease progression

A team from UNIGE and HUG shows that the side where the first symptoms of the disease appear—left or right side of the body—influences patients' cognitive and emotional manifestations.

Parkinson's disease often begins asymmetrically, initially affecting either the right or left side of the body. A team from the University of Geneva (UNIGE) and the Geneva University Hospitals (HUG) demonstrates that this factor influences the progression of non-motor symptoms. Right-sided onset predicts more pronounced cognitive decline, while left-sided onset is associated with psychiatric disorders such as anxiety or depression.

Published in npj Parkinson's Disease, these results highlight the importance of personalized care.


Parkinson's disease affects approximately 10 million people worldwide. It typically begins asymmetrically, initially affecting only one side of the body. While it first manifests with motor symptoms—such as tremors, slowness of movement, or muscle rigidity—it also leads to cognitive, anxiety, or depressive disorders, whose progression remains poorly studied.

These results represent a crucial advance in the study of the disease's non-motor symptoms, long underestimated by research.

In recent work, a team from UNIGE and HUG shows for the first time that the side of symptom onset influences not only motor disorders but also the cognitive and emotional manifestations of the disease. Thus, patients with motor symptoms on the right side (signs of left brain hemisphere dysfunction) exhibit more global cognitive decline and a higher risk of dementia, while individuals with symptoms on the left side (right hemisphere dysfunction) more frequently face psychiatric problems such as depression, anxiety, and impaired emotion recognition.

For personalized care

"These results constitute a crucial advance for the study of the disease's non-motor symptoms, long underestimated by research," explains Julie Péron, associate professor at the Clinical and Experimental Neuropsychology Laboratory of the Faculty of Psychology and Educational Sciences and at the Center for Affective Sciences of UNIGE, as well as at the Neurology Service of the Department of Clinical Neurosciences at HUG, who led this work.

The study argues for systematic integration of this symptomatic variable during diagnosis to ensure personalized care for affected individuals. "This consideration would allow for true anticipation and guidance of the person toward targeted therapies based on their Parkinsonian pattern," indicates Philippe Voruz, postdoctoral researcher at the Clinical and Experimental Neuropsychology Laboratory of the Faculty of Psychology and Educational Sciences at UNIGE, at the Neurosurgery Service of HUG, and at the Laboratory of Biological Geochemistry at EPFL, first author of the study.

These results were obtained through the analysis of 80 studies published on the subject over the past five decades. For the research team, the next step will involve addressing several methodological questions—for example, how do we precisely measure disease asymmetry based on observable symptoms?—and verifying their results on other disorders related to the disease.