Olfactory swab sampling optimization for α-synuclein aggregate detection in patients with Parkinson’s disease

Abstract

Background In patients with Parkinson’s disease (PD), real-time quaking-induced conversion (RT-QuIC) detection of pathological α-synuclein (α-syn) in olfactory mucosa (OM) is not as accurate as in other α-synucleinopathies. It is unknown whether these variable results might be related to a different distribution of pathological α-syn in OM. Thus, we investigated whether nasal swab (NS) performed in areas with a different coverage by olfactory neuroepithelium, such as agger nasi (AN) and middle turbinate (MT), might affect the detection of pathological α-syn. Methods NS was performed in 66 patients with PD and 29 non-PD between September 2018 and April 2021. In 43 patients, cerebrospinal fluid (CSF) was also obtained and all samples were analyzed by RT-QuIC for α-syn. Results In the first round, 72 OM samples were collected by NS, from AN (NSAN) or from MT (NSMT), and 35 resulted positive for α-syn RT-QuIC, including 27/32 (84%) from AN, 5/11 (45%) from MT, and 3/29 (10%) belonging to the non-PD patients. Furthermore, 23 additional PD patients underwent NS at both AN and MT, and RT-QuIC revealed α-syn positive in 18/23 (78%) NSAN samples and in 10/23 (44%) NSMT samples. Immunocytochemistry of NS preparations showed a higher representation of olfactory neural cells in NSAN compared to NSMT. We also observed α-syn and phospho-α-syn deposits in NS from PD patients but not in controls. Finally, RT-QuIC was positive in 22/24 CSF samples from PD patients (92%) and in 1/19 non-PD. Conclusion In PD patients, RT-QuIC sensitivity is significantly increased (from 45% to 84%) when NS is performed at AN, indicating that α-syn aggregates are preferentially detected in olfactory areas with higher concentration of olfactory neurons. Although RT-QuIC analysis of CSF showed a higher diagnostic accuracy compared to NS, due to the non-invasiveness, NS might be considered as an ancillary procedure for PD diagnosis.

Combining skin and olfactory α-synuclein RT-QuIC - towards biomarker-driven phenotyping in synucleinopathies

“…We detected α-syn aggregation in 10% of control subjects, who reported some symptoms that could be attributable to prodromal PD, however, none of them reached a diagnostic certainty level needed to diagnose prodromal PD according to current research criteria 16 . These results are similar to those previously reported 10,23 and are in line with the frequency of incidental Lewy body disease (10-12%) found in the population of > 60 year-olds post-mortem 30 . Larger prospective studies of control subjects could be of value, particularly given the non-invasiveness of nasal brushings.…”

“…Our study included a signi cantly smaller iRBD cohort (n = 18), the majority of whom (n = 12) were positive in nasal RT-QuIC, possibly preventing us from seeing any correlation of the clinical data with a binary RT-QuIC outcome. Interestingly, in the case of PD, such correlation was not seen in the study by Stefani et al More recently 23 , similarly to our study (Table 2), it was demonstrated that signi cant number of patients with preserved olfaction tested positively for nasal RT-QuIC. This could indicate that hyposmia has a different pathoanatomic basis in the iRBD and PD groups, i.e.…”

“…While using immunohistochemistry for quality control, we did not nd a smaller number of olfactory neurons in patients with negative RT-QuIC results. It was recently shown that the sensitivity of α-syn detection differed from 45% in the middle turbinate (concha) to 84% when sampled more superiorly -from the agger nasi, correlating with the abundance of olfactory neurons in the two regions 23 . Indeed, according to a pathological study, olfactory mucosa was present in less than 20% of biopsies from middle turbinate 27 , so this anatomic sight should not be routinely used.…”

“…Combining skin biopsies with nasal brushings would not only result in more e cient α-syn detection but could lead to precise biomarker-based subtyping of patients 31 . Further optimization of the sampling procedures could increase the currently reported sensitivity 23 . Larger, ideally multi-center, studies that would include a parallel sampling of multiple tissues (CSF, skin, nasal brushings) are needed to better implement α-syn seeding assays into clinical practice.…”

Correction: Olfactory swab sampling optimization for α-synuclein aggregate detection in patients with Parkinson’s disease

“…In the original publication of this article [1], "AN" is missing in the column heading "Patients underwent NS at the (n = 46)" in Table 1 due to a typesetting error. The correct column heading should be "Patients underwent NS at the AN (n = 46)".…”