Alpha-synuclein seeding activity in postmortem tissues from patients with diffuse and isolated Lewy bodies.

We have evaluated the diagnostic potential of the seeding amplification assay (SAA) in detecting α-synuclein seeding activity in postmortem brain and cerebrospinal fluid (CSF) samples from patients with primary and co-pathology α-synucleinopathies. Moreover, we investigated potential SAA positivity in control samples which may suggest unrecognized co-pathology. A total of 15 brain and 14 CSF samples with definite dementia with Lewy bodies (DLB, n = 6), Alzheimer´s disease with amygdala Lewy body (AD/ALB, n = 3), and patients with concomitant Creutzfeldt-Jakob disease and Lewy body pathology (CJD/LBP, n = 6) comorbidity were tested for α-synuclein seeding activity using SAA assay utilizing recombinant α-synuclein (WT) with N-terminal His-tag. Control samples consisted of other neurodegenerative diseases (n = 17 for brain and n = 18 for CSF samples) and healthy corneal donors (n = 17). The analysis of seeding activity in brain samples suggested 100% sensitivity and 91.2% specificity. Five out of 34 brain control samples gave a positive SAA outcome. However, upon reevaluation, two of these samples were reclassified as Alzheimer´s disease (AD) with synucleinopathy co-pathology. The analysis of CSF also suggested 100% sensitivity and 94.4% specificity, although dilution of some samples was necessary to decrease the effect of inhibitors. We report a good performance of the SAA not only in postmortem samples from primary synucleinopathies with advanced pathology, but also in co-pathology synucleinopathies with isolated Lewy bodies in the amygdala in AD cases. Our findings highlight the importance of careful diagnostic evaluation in AD patients, where co-existing synucleinopathy may otherwise go unrecognized.