ABSTRACT
INTRODUCTION: Myotonic dystrophy type 1 is a neuromuscular, degenerative and progressive disease, with an autosomal dominant pattern of inheritance, variable expressivity and incomplete penetrance. The genetic defect is an unstable mutation due to the expansion of the triplet CTG in the 3 unstranslated region at the DMPK gene on chromosome 19q13.3. OBJECTIVE: The main objective was to study the intergenerational behavior of the DM1 mutation in order to evaluate the importance of this disease as a neurological problem that could be manageable by genetic counseling. PATIENTS AND METHODS: The study involved 84 patients with clinical diagnosis of DM1 and their relatives, which were confirmed through molecular diagnosis using Southern blot and PCR. RESULTS: Data analysis reveals the size of the mutation presents a positive correlation with the severity of the symptoms and a negative correlation with the age of onset. Transmission of the DM1 mutation is sex and size dependent among the Costa Rican patients. There is an important increment in the size of the mutation between generations and there are no differences in mutation size respect to the transmitting sex. CONCLUSION: The worldwide intergenerational behavior of the DM1 mutation is similar in Costa Rica
