MiRNAs are small single-stranded noncoding RNAs, which are known to regulate gene expression by reducing mRNA stability and translation. miRNAs and their biogenesis machinery are involved in the development of various disease, such as cancer, cardiovascular disease, and neurodegenerative disease.

 MiRNA expression level changes in MSA and PD have been studied in serum and CSF, but number of studies describing changes in plasma samples is limited.

 To identify miRNAs that are up-regulated or down-regulated in plasma of MSA patients, we performed one-channel microarray analysis using 3D-gene® Human miRNA oligo chips (ver. 17), which analyze 1720 miRNAs. Plasma samples were obtained from 11 clinically probable MSA-C patients and six healthy controls.

 To validate the result of microarray analysis, reverse transcript qPCR (RT-qPCR) of plasma miRNAs that showed different expression levels in microarray analysis was performed using SYBR Green qPCR analysis. For RT-qPCR, we enrolled 31 clinically probable MSA-C patients, 30 clinically probable MSA-P patients, 28 PD patients, and 30 healthy controls.

 Clinical diagnoses of MSA were made based on the second consensus statement on the diagnosis of MSA.

 In microarray analysis, we identified 4 up-regulated miRNAs and 16 down-regulated miRNAs.

 In RT-qPCR, we identified three miRNAs with differing expression levels between groups. hsa-miR-671-5p was expressed lower in PD and MSA-P compared to MSA-C and controls. Hsa-miR-19b-3p showed a higher expression level in PD compared to others. Hsa-miR-24-3p was up-regulated in PD compared to MSA-C. Interestingly, expression levels of hsa-miR-19b-3p and hsa-miR-24-3p were strongly correlated.

 We identified several miRNAs that are differently expressed in PD and MSA patients. These miRNAs might become useful tools for differential diagnosis or the pathophysiological research of these conditions.