Digital PCR quantification of miR-30c and miR-181a as serum biomarkers for Duchenne muscular dystrophy.

Circulating microRNAs (miRs/miRNAs) are being used as non-invasive biomarkers for diagnosis, prognosis and efficiency of clinical trials. However, to exploit their potential it is necessary to improve and standardize their detection. In a previous study, we identified two microRNAs, miR-30c and miR-181a, that appear to be key regulators of muscular dystrophy. We hypothesized that they could represent useful biomarkers of Duchenne and Becker muscular dystrophies (DMD and BMD). The objective of this study was to assess the absolute levels of miR-30c and miR-181a in sera of DMD and BMD patients using digital PCR (a robust technique for precise and direct quantification of small amounts of nucleic acids without standard curves and external references), and investigate the correlation between miR-30c and miR-181a expressions and several clinical parameters. Our results show that the serum levels of miR-30c and miR-181a increased 7- and 6-fold respectively in DMD patients (n = 21, 2-14 years, ambulant), and 7-fold in BMD patients (n = 5, 9-15 years) compared to controls (n = 22, 2-14 years). No association between miRNA levels and age or corticosteroid treatment was detected in DMD. However, there was a trend towards higher levels of miR-30c in DMD patients with better preserved motor function according to various motor scales and timed tests. We demonstrate that digital PCR is a useful technique for accurate absolute quantification of microRNAs in sera of DMD/BMD patients. We propose miR-30c and miR-181a as reliable serum diagnostic biomarkers for DMD and BMD and miR-30c as a potential novel biomarker to assess disease severity in DMD.