Although the olfactory decline in Parkinson’s disease (PD) precedes the motor symptoms by several years or decades, it has yet to provide for a specific early biomarker in PD. Typical olfactory tests probe olfactory performance, in tasks such as detection, discrimination, and identification. Because of the myriad possible causes for the decline in olfactory performance, such performance-based tests lack specificity. An alternative to performance-based tests is the olfactory perceptual fingerprint (OPF). OPFs characterize how the world smells to an individual. OPFs are related to genetic makeup (Secundo et al., 2015), and provide specificity where performance-based tests do not (Weiss et al., 2020). To test the hypothesis that PD is associated with a specific typical OPF, we tested 10 PD patients (9M, mean age = 66.3 ± 7.4 years, disease duration = 9.3 ± 7.9 years, MDS-UPDRS total score = 57.9 ± 21.6) and 10 healthy controls (9M, mean age = 64.9 ± 5.4 years) using 10 odors and 11 descriptors. We found that OPFs were similar within the two groups but significantly different between them. In other words, healthy participants had higher descriptor correlations with other healthy participants, rather than with the PD group (paired t-test, t(8)=-3.05, P=.01), and PD participants had higher descriptor correlations with other PD participants, rather than with the healthy group (paired t-test, t(8)=-2.46, P=.03). Moreover, we could use OPFs alone to classify PD (unsupervised k-means clustering, 90% specificity, 70% sensitivity). These pilot data raise the possibility of a specific olfactory biomarker in PD.

References:
Secundo L, Snitz K, Weissler K, et al. (2015). Individual olfactory perception reveals meaningful nonolfactory genetic information. PNAS. 112:8750-5.
Weiss T, Soroka T, Gorodisky L, et al. (2020). Human Olfaction without Apparent Olfactory Bulbs. Neuron. 105:35-45.e5.