Identifying early cognitive patterns in Parkinson’s disease

Parkinson's disease is usually diagnosed when the neurodegenerative process in the brain is very advanced. On average, the disease is diagnosed when about 60% of the susceptible dopamine-producing nerve cells have been lost, leading to the familiar motor symptoms of tremor and muscle rigidity. Most experts agree that the first cells affected by the disease are lost up to 20 years before the onset of these motor symptoms. Identifying methods for early detection is therefore a key research priority of the National Centre of Excellence in Research on Parkinson's Disease (NCER-PD), as it would allow protective strategies currently in development to be employed to at least slow the progression of the disease.

In a study recently published in the Journal of Parkinson's Disease, NCER-PD researchers analysed the cognitive symptoms in people at higher risk of developing Parkinson's disease. This risk estimation is based on a loss of smell and an increased likelihood of REM-sleep Behaviour Disorder (RBD) in participants in the Luxembourg Parkinson’s Study and the Luxembourg National Sleep Study, compared to a group of controls without these risk factors. As this particular sleep disorder and olfactory dysfunction are known to be relevant early signs of Parkinson's disease, they are useful indicators for identifying people who may be in the early stages of the disease without showing obvious motor symptoms.

“We found that people with a higher risk of developing Parkinson's disease already show global but also specific cognitive deficits. These include difficulties with visuo-constructive tasks, which require the ability to process visual information correctly, for example when copying a complex geometric figure. Furthermore, mental flexibility, a cognitive process needed to efficiently switch between tasks, seems to be particularly impaired in these people,” explains Dr Laure Pauly, first author of the publication. These findings fit with the observation that approximately half of people with Parkinson’s disease have similar cognitive impairments at the time of diagnosis. “We also found higher levels of depression, apathy and lower self-reported quality of life in people at higher risk to develop Parkinson’s disease. Taken together, these findings confirm that distinct non-motor patterns may manifest years before the diagnosis of the disease,” she adds.

Participants in the current study will be followed up annually to track changes in their non-motor profiles, including cognition, mood and quality of life assessments, and the possible development of motor symptoms leading to the diagnosis of Parkinson's disease. “What is particularly important about our study is that our participants may help us to get insight into the very early stages of a process that may finally lead to Parkinson’s disease. This allows us to collect highly relevant information on different cognitive profiles, potentially allowing earlier detection of the disease,” explains Prof. Rejko Krüger, coordinator of NCER-PD. “This study highlights the importance and feasibility of identifying the early indicators and risk factors for Parkinson’s disease. These would allow us to identify people at high risk and apply preventive measures, a concept already established in the pdp programme for people at high risk of dementia.”

To identify additional risk factors, researchers are now analysing data from the recently completed first phase of the Healthy Brain Ageing (HeBA) study. Participants who appear to be at particularly high or low risk of developing a neurodegenerative disease such as Parkinson's, based on their answers to an online questionnaire, have been invited to take part in the next steps of the study, which include a smell test at home and an invitation to the research clinic.