Association between the Amplification Parameters of the α‐Synuclein Seed Amplification Assay and Clinical and Genetic Subtypes of Parkinson's Disease

BACKGROUND: α-Synuclein seed amplification assay on cerebrospinal fluid (CSF-αSyn-SAA) has shown high accuracy for Parkinson's disease (PD) diagnosis. The analysis of CSF-αSyn-SAA parameters may provide useful insight to dissect the heterogeneity of synucleinopathies. OBJECTIVE: To assess differences in CSF-αSyn-SAA amplification parameters in participants with PD stratified by rapid eye movement (REM) sleep behavior disorder (RBD), dysautonomia, GBA, and LRRK2 variants. METHODS: (T50), time to threshold (TTT), slope, and area under the curve (AUC). Sporadic PD (n = 371) was stratified according to RBD and dysautonomia (DysA) symptoms. Genetic PD included carriers of pathogenic variants of GBA (GBA-PD, n = 52) and LRRK2 (LRRK2-PD, n = 124) gene. RESULTS: CSF-αSyn-SAA was positive in 77% of LRRK2-PD, 92.3% of GBA-PD, and 93.8% of sporadic PD. The LRRK2-PD cohort showed longer T50 and TTT, and smaller AUC than GBA-PD (P = 0.029, P = 0.029, P = 0.016, respectively) and sporadic PD (P = 0.034, P = 0.033, P = 0.014, respectively). In the sporadic cohort, CSF-αSyn-SAA parameters were similar between PD with (n = 157) and without (n = 190) RBD, whereas participants with DysA (n = 193) presented shorter T50 (P = 0.026) and larger AUC (P = 0.029) than those without (n = 150). CONCLUSION: CSF-αSyn-SAA parameters vary across genetic and non-genetic PD subtypes at the group level. These differences are mostly driven by the presence of LRRK2 variants and DysA. Significant overlaps in the amplification parameter values exist between groups and limit their use at the individual level. Further studies are necessary to understand the mechanisms of CSF-αSyn-SAA parameter differences. © 2024 International Parkinson and Movement Disorder Society.