Molecular-genetic studies of inherited myotonic conditions in Costa Rica

Introduction: Hereditary myotonias are a clinically and genetically heterogeneous group of skeletal muscle diseases characterized by myotonia (delayed muscle relaxation). Clinically, they are classified as dystrophic and non-dystrophic myotonias, which are caused by mutations in the DNA. Aim: Describe the most relevant findings on some hereditary myotonias in Costa Rica. Methodology: Genetic-molecular studies of these diseases were carried out in individuals affected with a myotonic condition and their relatives at genetic risk. Results: The mutation for myotonic dystrophy type 1 (DM1) was found in 246 individuals. We have seen an improvement in the correlations between the size of the mutation and the age of onset of symptoms, in addition we have demonstrated the modifying role of some genetic factors in DM1. Of 18 patients who were negative for the mutation causing DM1, in eight families, a mutation was identified in genes, that provide the instructions for producing proteins called ion channels. Analyzes at the functional level helped to show that these mutations cause structural changes that modify the properties of these channels, causing a loss or gain of channel function. Conclusions: Our studies have allowed a correct clinical classification for many patients with these pathologies, in addition to explore the genetic and molecular basis of the clinical variability of these diseases, by searching for DM1 modifying factors and functional studies of new mutations that cause hereditary channelopathies, which is key to provide genetic counseling to patients and families and treating the disease in the most appropriate way.