ABSTRACT
AIM: The aim is to review the molecular and genetic aspects of the dystrophic and no dystrophic myotonias. BACKGROUND: Myotonic diseases are hereditary conditions of the skeletal muscle, classified in two groups depending on the symptoms. In the first group are the myotonic dystrophies, with the myotonic dystrophies type 1 and 2. In the second group are the channelopathies, characterized for the affected function of the ion channels. Myotonic dystrophy type 1, a neurodegenerative, progressive and disabling disease is caused by an expansion of the CTG trinucleotide, its size shows a positive correlation with the severity and negative with age of onset. There are enough insights to think that the gain of function of the mutant ARN is the pathophysiological mechanism occurring on this disease. Myotonic dystrophy type 2, less severe than type 1, is caused by an expansion of the CCTG tetranucleotide, its pathophysiological mechanism is similar to that one proposed for the type 1. In the second group we can find the chloride channelopathies, with autosomal dominant or recessive inheritance, caused by one of the 60 different mutations on the chloride channel gene; and the sodium channelopathies, group of three clinically overlapping diseases, with dominant heredity caused by one of the 25 different mutations on the sodium channel gene. CONCLUSIONS: These diseases are highly clinically variable, and even though their genetic base is known, it is necessary too much research in order to understand their pathophisiology and the phenotype genotype relationships.
Subject(s)
Myotonic Disorders/genetics , 3' Untranslated Regions/genetics , Age of Onset , Chloride Channels/deficiency , Chloride Channels/genetics , Chromosomes, Human, Pair 19/genetics , Gene Frequency , Humans , Ion Channels/deficiency , Ion Channels/genetics , Ion Channels/physiology , Muscle Proteins/deficiency , Muscle Proteins/genetics , Muscle Proteins/physiology , Myotonic Disorders/classification , Myotonic Disorders/epidemiology , Myotonic Dystrophy/classification , Myotonic Dystrophy/epidemiology , Myotonic Dystrophy/genetics , Myotonin-Protein Kinase , NAV1.4 Voltage-Gated Sodium Channel , Paralysis, Hyperkalemic Periodic/genetics , Protein Serine-Threonine Kinases/deficiency , Protein Serine-Threonine Kinases/genetics , RNA-Binding Proteins/genetics , Sodium Channels/deficiency , Sodium Channels/genetics , Trinucleotide Repeat ExpansionABSTRACT
Objetivo. Revisar los aspectos genéticos y moleculares de las miotonías distróficas y no distróficas. Desarrollo. Las enfermedades miotónicas son condiciones hereditarias del músculo esquelético, las cuales se pueden clasificar en dos grupos según el cuadro clínico. Al primer grupo pertenecen las miotonías distróficas, donde se encuentran las distrofias miotónicas (DM) tipo 1 y 2.Al segundo grupo pertenecen las canalopatías, que se caracterizan por presentar alteraciones de la función en los canales iónicos. La DM tipo 1, enfermedad neurodegenerativa, progresiva y discapacitante, la causa una expansión del trinucleótido CTG, cuyo tamaño muestra correlación positiva con la gravedad y negativa con la edad de manifestación. Existe evidencia suficiente para pensar que el mecanismo fisiopatológico de la enfermedad es la ganancia de función del ARN mutado. La DM tipo 2, menos grave que la tipo 1, la causa una expansión del tetranucleótido CCTG, cuyo mecanismo fisiopatológico es similar al propuesto para la tipo 1. En el segundo grupo se encuentran las canalopatías de cloruro, de herencia autosómica dominante o recesiva, causadas por una de las 60 diferentes mutaciones en el gen del canal de cloruro, y las canalopatías de sodio, grupo de tres enfermedades que se solapan clínicamente, de herencia dominante, causadas por una de las 25 diferentes mutaciones en el gen del canal de sodio. Conclusiones. Estas enfermedades son clínicamente muy variables; no obstante, su base genética se conoce; falta todavía mucha investigación para lograr entender su fisiopatología y las relaciones genotipo-fenotipo (AU)
Subject(s)
Humans , Muscle Proteins , Myotonic Disorders , Trinucleotide Repeat Expansion , Sodium Channels , Protein Serine-Threonine Kinases , Paralysis, Hyperkalemic Periodic , Ion Channels , Gene Frequency , Myotonic Dystrophy , 3' Untranslated Regions , Chloride Channels , Chromosomes, Human, Pair 19 , Age of Onset , Gene Frequency , RNA-Binding ProteinsABSTRACT
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
