Skin Seed Amplification Assay Differentiates Multiple System Atrophy from Parkinson's Disease
Anastasia Kuzkina, Diego Rodriguez, Celine Panzer, Alain Ndayisaba, Antonia Kohl, Shreya Rai, Breelyn Gilbert, Bruno Hammerschlag, Karie Shen, Lisa Harder‐Rauschenberger, Olivia Laun, Julia Meehan, Sucika Perumalla, Elena Salabasidou, Kristie Jones, Dalina Ceku, Robert Blum, Susanne Knorr, Camelia M. Monoranu, Claudia Sommer, Jens Volkmann, Barbara K. Changizi, Kathrin Doppler, Vikram KhuranaAbstract
Background
Misdiagnoses of multiple system atrophy (MSA) and Parkinson's disease (PD) remain common.
Objective
The objective of the study was to develop a skin α‐synuclein seed amplification assay (αSyn‐SAA) for detecting pathological α‐synuclein and distinguishing MSA from PD.
Methods
In this blinded, cross‐sectional study, 308 skin biopsies from 117 participants were analyzed using a standardized thioflavin T fluorescence‐based αSyn‐SAA protocol. The cohort included 42 PD, 31 MSA, 30 controls, and 14 progressive supranuclear palsy (PSP) cases. Kinetic parameters were analyzed to differentiate PD from MSA, and matched skin cerebrospinal fluid (CSF)/magnetic resonance imaging (MRI) analyses were performed. Assay thresholds were predefined using brain lysates from neuropathologically confirmed cases. Fibril morphology from amplified skin samples was compared to postmortem brain using proteinase K digestion and electron microscopy.
Results
αSyn‐SAA detected synucleinopathy (PD or MSA) with 82.2% sensitivity and 90% specificity versus controls. Receiver operating characteristic (ROC) analysis showed that maximum fluorescence ( F max , area under the curve [AUC] = 0.93) and lag time (AUC = 0.91) distinguished PD from MSA at the biopsy level. SAA positivity correlated with rapid eye movement (REM) sleep behavior disorder (RBD) in both disorders. Among SAA‐positive cases, the 50% mean F max cutoff correctly classified the underlying synucleinopathy in 81.7% of cases (49 of 60). Disease‐specific kinetic and structural signatures were reproducible across laboratories and αSyn substrate batches and were supported by concordant findings in a subset of skin samples matched to CSF, MRI data, and postmortem brain tissue.
Conclusion
Skin αSyn‐SAA detects pathological α‐synuclein in living patients with high accuracy and distinguishes MSA from PD based on assay kinetics and fibril strain properties, supporting its potential as a biomarker to distinguish among synucleinopathies. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.