Study of Ranolazine in Myotonia Congenita, Paramyotonia Congenita and Myotonic Dystrophy Type 1

The purpose of this study is to gather preliminary data to determine if ranolazine is a safe and effective treatment for the symptoms of myotonia congenital, paramyotonia congenita, and myotonic dystrophy type 1. The duration of the study is 5 weeks.

Recent advances in the understanding of myotonia congenita have identified potential areas that could possibly respond to treatment in a drug study. The drug ranolazine (trade name Ranexa) is a FDA-approved medication to treat chest pain in patients with heart disease. Ranolazine has been studied in mice with myotonia congenita. The data from this animal model suggest that ranolazine may improve the symptoms and signs of myotonia. All individuals that participate will be placed on active drug. The investigators want to see if this drug is safe to take without causing too many side effects for people with myotonia congenita, paramyotonia congenital and myotonic dystrophy type 1. Participants will go to The Ohio State University for study visits. Participants will take ranolazine for four weeks. Participants can expect a total of 4 study visits and 2 phone calls over the 5 week period.