Circulating miR-30b-5p is up regulated in Cavalier King Charles Spaniels affected by early myxomatous mitral valve disease

There is a growing interest in developing new molecular markers of heart disease in young Cavalier King Charles Spaniels affected by myxomatous mitral valve disease. The aim of the study was to measure the abundance of 3 circulating microRNAs and their application as potential biomarkers in the plasma of Cavalier King Charles Spaniels with early asymptomatic myxomatous mitral valve disease. 33 dogs affected by the disease in American College of Veterinary Internal Medicine (ACVIM) stage B1 were divided in three groups (11 younger than 3 years, 11 older than 3 years and younger than 7 years, and 11 older than 7 years), and 11 healthy (ACVIM stage A) Cavalier King Charles Spaniels were included as the control group. This is a prospective cross-sectional study. The abundance of three circulating microRNAs (miR-1-3p, miR30b-5p, and miR-128-3p) was measured by quantitative real-time PCR using TaqMan® probes. Diagnostic performance was evaluated by calculating the area under the receiver operating curve (AUC). miR-30b-5p was significantly higher in ACVIM B1 dogs compared to ACVIM A subjects, and the area under the receiver operating curve was 0.79. According to the age of dogs, the abundance of miR-30b-5p was statistically significantly higher in group B1<3y (2.3 folds, P = 0.034), B1 3-7y (2.2 folds, P = 0.028), and B1>7y (2.7 folds, P = 0.018) than in group A. The area under the receiver operating curves were fair in discriminating between group B1<3y and group A (AUC 0.780), between B1 3-7y and A (AUC 0.78), and good in discriminating between group B1>7y and A (AUC 0.822). miR-30b-5p changed in the plasma of dogs at the asymptomatic stage of disease, particularly at a young age. ### Competing Interest Statement The authors have declared no competing interest.