“A puzzling, yet not very well known characteristic of Parkinson’s disease is that a great majority of the persons affected also have a problem with the sense of smell”, declares professor Johannes A. Frasnelli, of the Department of Anatomy at University du Québec à Trois-Rivières (UQTR). With time, this line of inquiry could lead to a major breakthrough in the early detection of the disease, as the smell dysfunction of parkinsonian patients could be diagnosed several years before the onset of motor symptoms.

The link between olfactory dysfunction and Parkinson’s disease is well established. Professor Frasnelli, who holds UQTR Research Chair in Chemosensory Neuroanatomy and is a member of the CogNAC Research Group on cognitive neurosciences at UQTR, explains: “We know that the zones of the brain responsible for olfactory processing are the first to be affected, at least ten years before those where the cradle of the motor system is to be found. So the idea is to detect the olfactory dysfunction early on, be it hyposmia [a reduced ability to smell] or anosmia [the loss of the sense of smell], and to use this information to develop early screening tests, in order to intervene and stop the progression of Parkinson’s disease.”

However, persons having a problem with the sense of smell (an estimated 20% of the population) will not necessarily develop Parkinson’s disease. So the challenge facing Johannes Frasnelli is to reliably discriminate between them and pinpoint those who could be affected by Parkinson’s disease. To provide support for this work, Parkinson Canada awarded the UQTR researcher a grant of 40 000$.

Determining a chemosensory impairment profile

Professor Frasnelli hopes to be able to find, among the patients with a dysfunctional sense of smell, a chemosensory impairment profile (i.e. linked to the chemical senses) specific to Parkinson’s disease.

Professor Johannes A. Frasnelli.

“Unlike the other senses (sight, hearing and touch) that react to physical stimulations, the chemical senses are stimulated by molecules present, for example, in food and perfumes”, he says. We human beings have three such senses, namely olfaction, taste, and what is called the trigeminal system. It is a sensory system in its own right; using both the oral and nasal passages, it induces the perception of sensations like the bite of hot pepper, the tingling of wasabi, or the refreshment of peppermint.

Contrary to persons with a dysfunction affecting both the sense of smell and the trigeminal system, the latter seems not to be impaired in parkinsonian patients. “Normally, in a patient with a reduced sense of smell, a reduction of the trigeminal system is also observed. Our hypothesis is that the sense of smell of a parkinsonian patient is reduced, but not the trigeminal system. We have preliminary data leading us in that direction”, he argues.

In this research project, Professor Frasnelli works in collaboration with Dr Pascali Durand-Martel, of the Neurology Department, CIUSSS-MCQ, and Parkinson Québec. The data is from the first phase of the study, which relies on three test groups, each one comprised of 30 persons. The first group is made up of parkinsonian patients, the second one of people with a dysfunctional sense of smell, and the third one is a control group (having neither Parkinson’s disease nor a dysfunctional sense of smell). The groups were submitted to several tests in order to stimulate the sense of smell and the trigeminal system.

As the premise of the second phase of the study relies on the hypothesis that the trigeminal system is not affected by the onset of Parkinson’s disease, Johannes Frasnelli hopes to discriminate between groups 1 and 2, and prove that it is possible to identify the persons at risk of developing Parkinson’s disease.