α-Synuclein Seed Amplification in CSF and Brain from Patients with Different Brain Distributions of Pathological α-Synuclein in the Context of Co-Pathology and Non-LBD Diagnoses

Abstract

Objective: The purpose of this study was to determine the sensitivity and specificity of α-synuclein seed amplification assay (αSyn-SAA) in antemortem and postmortem cerebrospinal fluid (CSF) of autopsy-confirmed patients with different distributions of pathological αSyn, co-pathologies, and clinical diagnoses.

Methods: The αSyn-SAA was used to test antemortem CSF samples from 119 subjects with a variety of clinical syndromes and standardized neuropathological examinations from Oregon Health and Science University (OHSU) and University of California San Diego (UCSD; 56 additional postmortem CSF samples available). The αSyn-SAA was also applied to frontal cortex and amygdala homogenates. Sensitivity and specificity were compared across distributions of αSyn pathology. Clinical data and co-pathologies were compared across αSyn-SAA positive and negative groups.

Results: Fifty-three individuals without and 66 with αSyn-pathology (neocortical [n = 38], limbic [n = 7], and amygdala-predominant [n = 21]) were included. There was a sensitivity of 97.8% and specificity of 98.1% of the αSyn-SAA to identify patients with limbic/neocortical pathology from antemortem CSF. Sensitivity to detect amygdala-predominant pathology was only 14.3%. Postmortem CSF and brain tissue αSyn-SAA analyses also showed higher assay positivity in samples from limbic/neocortical cases.

Interpretation: CSF αSyn-SAA reliably identifies αSyn seeds in patients with diffuse αSyn pathology in the context of co-pathology and non-Lewy body disease (LBD) diagnoses. The analysis of brain homogenates suggests that pathological αSyn in the amygdala might differ from pathological αSyn in the frontal cortex. The αSyn-SAA might facilitate the differential diagnosis of dementias with mixed pathologies. ANN NEUROL 2022;92:650-662.

Figure 1.. Kinetic parameters of Research SAA stratified by alpha-synuclein distribution.

A) Maximum Fluorescence Signal from R/D αSyn-SAA using antemortem CSF between no αSyn-pathology (n=51), Neocortex/Limbic (n=44), and Amygdala-predominant (n=21) groups. B) Representative figures of raw kinetic data from the Research SAA using antemortem CSF. Included are “negative” samples that are from no αSyn-pathology and amygdala-predominant individuals, and “positive” samples that are from neocortical and amygdala-predominant individuals. Statistical analysis using one-way ANOVA with Tukey’s multiple comparisons post hoc (A). Error bars represent Standard Error of the Mean (SEM).

Figure 2.. Differences in neuropathology scores between synuclein-pathology groups as a function of SAA result.

Bars represent the distribution of SAA positive or SAA negative within high (“H”) or low (“L”) categorization of ADNC, Braak, Thal, and Cerad neuropathological staging. Patients are further classified by limbic/neocortical (“L/N”) or amygdala-predominant (“A”) groups. Statistical analysis using Fisher’s exact test within synuclein-pathology group.

Figure 3.. Clinical and pathological differences between True Positive and False Negative.

A) Interval in years from lumbar puncture to death between True Positives (n=47) and False Negative (n=19) groups. B) Distribution of Neocortex/Limbic and Amygdala-predominant LRP in True Positive and False Negative groups for antemortem and postmortem CSF analysis. Number of patients in each category is indicated on the bar. Statistical analysis using Wilcoxon rank-sum test with post hoc pairwise comparisons from Dwass, Steel, Critchlow-Fligner method (A) or chi-square (B). Error bars represent Standard Error of the Mean (SEM).