Serum miR-34a-5p, miR-103a-3p, and miR-376a-3p as possible biomarkers of conversion from relapsing-remitting to secondary progressive multiple sclerosis

Relapsing-remitting (RR) Multiple Sclerosis (MS) is the most common form of the disease; RRMS patients can maintain their clinical phenotype throughout life or can develop a secondary progressive (SP) course over time. We investigated whether circulating miRNAs can predict RR-to-SPMS conversion. A serum miRNAs profile was initially analyzed in a cross-sectional study by qPCR in 16 patients (8 RRMS and 8 SPMS) (Discovery cohort). Three miRNAs, i.e. miR-34a-5p, miR-103a-3p and miR-376a-3p, were significantly up-regulated in SPMS compared to RRMS patients (p < 0.0 5). Serum concentration of the same miRNAs was subsequently analyzed in a retrospective study by ddPCR at baseline in 69 RRMS patients who did (N = 36 cSPMS) or did not (N = 33) convert into SPMS over a 10-year observation period (Study cohort). The results showed that these miRNAs were significantly increased at baseline only in those RRMS patients who converted to SPMS over time. miR-34a-5p and miR-376a-3p alone were significantly increased in cSPMS sera at the end of the 10-years period too. Serum concentration of miR-34a-5p, miR-103a-3p and miR-376a-3p is increased in RRMS patients several years before their conversion to SPMS. These miRNAs might be useful biomarkers to predict the conversion from RRMS to SPMS.