Designing gRNAs to reduce the expression of the DMPK gene in patients with classic myotonic dystrophy

Myotonic dystrophy is a condition that affects thousands globally. It presents as a wide variety of life-threatening conditions, ranging from cardiac conduction defects and myotonia, to diabetes mellitus and hypogonadism. Myotonic dystrophy is mainly caused by the presence of trinucleotide repeats in the myotonic dystrophy protein kinase (DMPK) gene, which controls the function of muscle cells, and it currently has no cure. As this condition has a genetic cause, we hypothesized that we could design guide RNA (gRNA) sequences—short RNAs that direct DNA editing—specific to the trinucleotide repeats of the DMPK gene that cause myotonic dystrophy. This was extremely important, as these sequences could be used to target these repeats and ultimately suppress the effects of myotonic dystrophy for patients. To accomplish this, we located the sequence of the DMPK gene and used it to develop gRNA sequences. To analyze these gRNAs, we generated scores for binding efficiency with CRISPRedict. The sequences demonstrated overall middle to high scores for overall efficiency category, an on-target category, and an off-target category. All of the gRNAs we generated were predicted to bind to the DMPK gene with a stronger affinity than a random sequence, but a lower affinity than a sequence known to target DMPK. The highest overall efficiency score of any of the generated gRNAs was 0.631, which was similar to the score of a sequence known to effectively reduce DMPK expression. These gRNAs have the potential to effectively target the repeats in DMPK. They may be promising therapeutics to reduce the symptoms caused by myotonic dystrophy, potentially improving the quality of life of millions with the disease.