[Molecular and genetic aspects of the myotonic conditions].
OBJECTIVE
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.
Morales Montero
F
F
Instituto de Investigaciones en Salud y Escuela de Biologia, Universidad de Costa Rica., San Jose, Costa Rica. famorale@cariari.ucr.ac.cr
Cuenca Berger
P
P
D020413:3' Untranslated Regions / Q000235:genetics; D017668:Age of Onset; D018118:Chloride Channels / Q000172:deficiency / Q000235:genetics; D002888:Chromosomes, Human, Pair 19 / Q000235:genetics; D005787:Gene Frequency; D006801:Humans; D007473:Ion Channels / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D020967:Myotonic Disorders / Q000145:classification / Q000453:epidemiology / Q000235:genetics*; D009223:Myotonic Dystrophy / Q000145:classification / Q000453:epidemiology / Q000235:genetics; D065636:Myotonin-Protein Kinase; D062553:NAV1.4 Voltage-Gated Sodium Channel; D020513:Paralysis, Hyperkalemic Periodic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics; D015222:Sodium Channels / Q000172:deficiency / Q000235:genetics; D019680:Trinucleotide Repeat Expansion
D020413:3' Untranslated Regions; C086321:CLC-1 channel; C433227:CNBP protein, human; D018118:Chloride Channels; C585517:DMPK protein, human; D007473:Ion Channels; D009124:Muscle Proteins; D062553:NAV1.4 Voltage-Gated Sodium Channel; D016601:RNA-Binding Proteins; C106251:SCN4A protein, human; D015222:Sodium Channels; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases