Alpha-synuclein is increased in erythrocytes in parkinson’s disease cases

Idiopathic Parkinson's disease (iPD) is the second most common neurodegenerative disease after Alzheimer's disease (AD). Mutations in the SCNA gene, which encodes the protein alpha synuclein (α-syn), are associated with familial forms of Parkinson's disease (PD). Additionally, Lewy bodies (LBs) rich in α-synuclein are a hallmark of idiopathic Parkinson's disease (iPD) pathology. Unlike AD, there are no effective blood-based diagnostic assays for iPD. Recent studies show that measures of misfolded α-syn in cerebrospinal fluid (CSF) and skin biopsies reflect the diagnosis of iPD. The presence of misfolded α-syn suggests that the altered cellular processes in the brain that lead to aggregated α-syn may also occur in the periphery. However, CSF and skin biopsies are intrusive, highlighting the need for a blood-based diagnostic assay. Erythrocytes are the richest source of α-syn in the body, and we hypothesized that peripheral α-syn changes could be detected in erythrocytes in iPD. To test this hypothesis, we used a targeted liquid chromatography-mass spectrometry (LC-MS) assay, that included ¹⁵N-enriched recombinant α-syn as an internal standard. We compared the levels of α-syn in erythrocytes from iPD patients, AD patients, and healthy controls (CN). α-syn concentrations were significantly elevated in iPD (48.1 (29.7) µg mL^-1 of erythrocytes, median (IQR)) compared to CN (36.1 (28.4) µg mL^-1) and no difference was observed in AD (33.5 (18.1) µg mL^-1). Although α-syn levels were significantly elevated in iPD, the receiver operating characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.62, indicating that erythrocytic α-syn levels alone are not sufficient for diagnostic purposes.