Diagnosing α-synucleinopathies and assessing target engagement in trials is hindered by the lack of reliable biomarkers. Here, we introduce a first-in-kind quantitative, highly sensitive, and disease-specific diagnostic assay, named Seeding Amplification ImmunoAssay (SAIA), developed and validated to detect synucleinopathy-linked disorders. To this end, we used wide range of specimens, including 38 brain homogenates (BH) and 559 cerebrospinal fluid (CSF) samples from subjects with diverse synucleinopathy disorders, non-synucleinopathy diseases, idiopathic REM sleep behavior disorder (iRBD), and controls. SAIA generated robust results detecting disease-related α-synuclein seeds in BH samples at attogram levels, as referenced to preformed fibrils of α-synuclein. Furthermore, we conducted side-by-side comparisons between SAIA and a traditional Seeding Amplification Assay (SAA), which revealed high concordance. Further, SAIA distinguished synucleinopathies from non-synucleinopathies and controls with sensitivities and specificities ranging between 80-100% and area under the curve values exceeding 0.9. SAIA also accurately identified 24/24 (100%) iRBD cases, considered a prodromal state of PD, with 100% sensitivity and 80% specificity. Further optimization of SAIA through timepoint analyses revealed that shorter incubation times enhanced the assay's specificity for distinguishing MSA from PD highlighting the potential for improved differentiation between specific synucleinopathies. In conclusion, SAIA represents a novel, high-throughput method to screen, diagnose, and monitor synucleinopathy disorders in living subjects, offering significant improvements over existing methods through its quantitative output, shorter incubation time, and simplified workflow, features that enhance its suitability for clinical trial applications.
Keywords: SAA; biomarkers; immunoassays; synucleinopathies; α-synuclein.
A new sensitive test to detect early Parkinson's and related brain disorders using brain and spinal fluid samplesParkinson's disease and related conditions, known as synucleinopathies, are caused by the buildup of a protein called alpha-synuclein in the brain. Diagnosing these conditions early and accurately is a major challenge, especially before obvious symptoms appear. It is also difficult to track how well treatments work in clinical trials because current tests are not sensitive or specific enough. In this study, researchers developed a new laboratory test called the Seeding Amplification ImmunoAssay (SAIA). This test can detect very small amounts of abnormal alpha-synuclein proteins in samples taken from the brain and spinal fluid (cerebrospinal fluid or CSF). The test was designed to be both highly sensitive and specific to diseases like Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. The team tested SAIA on a wide range of samples from people with different brain conditions, including 38 brain tissue samples and 559 CSF samples. These came from individuals with synucleinopathies, nonrelated brain conditions, a sleep disorder called iRBD (which can be an early sign of Parkinson's), and healthy individuals. The new test successfully detected disease-linked alpha-synuclein proteins, even in extremely small amounts. Importantly, SAIA was able to clearly distinguish people with synucleinopathies from those without, and it identified all 24 iRBD cases correctly, showing promise for detecting disease even before major symptoms appear. The researchers also found that testing the samples for a shorter time improved the ability to tell different types of synucleinopathies apart, such as Parkinson's versus multiple system atrophy. In summary, SAIA is a promising tool for improving early diagnosis, helping select the right patients for clinical trials, and tracking how well new treatments are working.