Diagnóstico y tamizaje del retardo mental hereditario más común, situación en Costa Rica / I commonest diagnose and tamizaje of the hereditary mental retardation, situation in Costa Rica

El síndrome del cromosoma X frágil (FRAXA) es la segunda causa genética de retardo mental y la forma más frecuente de retardo mental hereditario. FRAXA es causante de discapacidades que van desde grados variables de problemas de aprendizaje hasta retardo mental. Con frecuencia se asocian retrasos severos en el lenguaje, problemas de conducta, comportamiento semejante al autista, testículos agrandados, orejas grandes o prominentes, hiperactividad, retraso en el desarrollo motor y deficiente integración sensorial. Se hace un resumen del conocimiento actual de esta patología y del trabajo de los autores. Se tocan temas como el producto génico, los métodos de diagnóstico, el cuadro clínico, la epidemiología, la prevención, el tratamiento, el tamizaje y la situación en Costa Rica.

Fragile X syndrome (FRAXA) is the most common type of hereditary mental retardation, and the second commonest with genetic origin. The range of affection in FRAXA includes from learning problems to mental retardation. The syndrome includes speech and language deficits, abnormal behaviours, including autistic features, macro orchidism, prominent ears, hyperactivity, sensorial integration and motor impairments. Actual data and the authors own work is reviewed. Topics approached are the gene product, diagnostic methodology, clinical picture, epidemiology, prevention, screening and the actual situation in Costa Rica regarding this pathology.

Disabilities caused by unstable mutations in Costa Rica

Myotonic dystrophy and fragile X syndrome are two genetically determined relatively common disabilities. Both are examples of a new type of mutation mechanism called unstable or dynamic mutations, triple repeats expansions or DNA amplification. Fragile X syndrome is recognized as the main cause of hereditary mental retardation and myotonic dystrophy is considered the most common muscular dystrophy of adults. This is a prospective non randomized study of clinically affected people, in order to confirm the diagnosis with molecular techniques (Southern blot and PCR) and to perform cascade screening of the rest of the family to offer them adequate genetic counseling. We were able to corroborate the initial diagnosis in most clinical cases of myotonic dystrophy, but in the cases of mental retardation more than half studies were negative for fragile X syndrome, stressing the difficulties encountered by medical practitioners to diagnose this syndrome. The reasons for this are several; probable the main culprit is the subtle and unspecific clinical picture affected individuals exhibit, particularly children before puberty. Cascade screening, genetic counseling and selective abortion are the only tools available to prevent these disabling diseases for the moment.

Las mutaciones inestables, nuevo reto para el consejo genético de enfermedades hereditarias: [revisión] / Unstable mutations, new challenges for genetic counseling of inherited disorders: [review]

Unstable mutations or amplification of DNA tandem repeats sequences constitute a new kind of genetic alteration discovered in the 90's that cause hereditary diseases. This mutation has been found inside or near important genes involved in the normal neurological function in human beings. In some cases, the presence of the amplification causes altered expression of the genes, their inactivation or the synthesis of a protein with new functions. Some common characteristics of these diseases are that they affect the central nervous system and are degenerative in nature. Most of them show genetic anticipation meaning that the severity of the manifestations increases in each generation and appear at an earlier age. In most cases, the severity of the symptoms is positively correlated with the size of the amplification. Twenty illnesses caused by this kind of mutations have been identified so far. Briefly, this work reviews the current knowledge about this topic.