"INTRODUCTION | Myotonic dystrophy type 1 (DM1) is a life threatening disease that causes severe physical and mental disabilities. Unfortunately, there are currently only symptomatic treatments for this condition. Therefore, our team aims at elaborating a new curative approach which consists in the silencing of the promoter of the gene with pathogenic excessive repeats (Myotonin-protein kinase or DMPK) using the CRISPRi system. METHODS | The ability of our CRISPRi system to inhibit the promoter of DMPK was tested in immortalized myoblasts from DM1 patients. For this purpose, lentiviral particles were produced using CRISPRi plasmids with their own sgRNAs. Next, these myoblasts were transduced and selected with blasticidin. Total DMPK mRNA was subsequently titrated by RT-qPCR and the density/size of nuclear DMPK RNA foci (ribonucleoproteic particles that are a hallmark of the disease) were determinated by FISH. RESULTS | Two out of 12 sgRNAs led to ~70% inhibition of DMPK transcription as well as a significant reduction of the intensity/number of foci in the cells. Other sgRNAs were less efficient or completely devoid of any activity. CONCLUSION | Our CRISPRi system is able to efficiently prevent the production of DMPK mRNA and formation of foci in pathological myoblasts. Further experiments will test whether functional abnormalities in pathological myocytes derived from the myoblasts can be rescued by our two most efficient CRISPRi constructs."