Testing the alpha-synuclein seed amplification assay in dementia with Lewy bodies across European countries

Background: The diagnosis of Dementia with Lewy Bodies (DLB) relies on clinical features and cognitive tests and is supported by imaging biomarkers. Although the new diagnostic criteria have improved diagnostic rates, DLB is still underdiagnosed. Therefore, there is a need for laboratory tests to enable a more accurate diagnosis of DLB. The alpha-synuclein seed amplification assay (SAA) has recently shown promising results for diagnosing DLB using various types of samples, including cerebrospinal fluid (CSF). One of the current barriers to scaling up and implementing SAA clinically is the use of different protocols across laboratories. It is currently unknown how these different protocols perform head-to-head, which will be relevant for multi-center studies and the clinical implementation of SAA. Methods: Our goal was to test the performance of SAA across three different labs using different SAA protocols. The study included 20 DLB patients (all DAT scan positive, 10 A positive, 10 A negative, 67.6 years old, 60 % male, with mild to moderate dementia) and 10 age- and sex-matched cognitively unimpaired controls, analyzed at all labs. Results: Our findings show that the diagnostic performance of SAA varied across laboratories. Lab A achieved 100% sensitivity and 100% specificity, although there were two cases with an unclear SAA result (excluded from the calculation of diagnostic performance). Lab B achieved 85% sensitivity and 90% specificity. Lab C achieved 80% sensitivity and 60% specificity. Formal statistical analyses showed a significantly lower sensitivity for Lab C compared to Lab A (p=0.042). The SAA result was significantly comparable in A positive and A negative DLB groups. Conclusion: On average, the three labs achieved 88% sensitivity and 83% specificity, highlighting the overall effectiveness of SAA in diagnosing DLB. Our next step is to propose an ad-hoc harmonization to reduce variation in assay performance across centres and clinics.