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      Síndrome frágil X Translated title: Fragile X Syndrome

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          Abstract

          Se efectuó una revisión sobre el síndrome frágil X, del cual en Cuba no existían reportes desde el punto de vista poblacional, hasta la realización del estudio psicopedagógico, social y clínico genético de las personas con retraso mental; mediante el cual pudo detectarse un total de 75 personas con defectos del gen FMR-1, que es el gen relacionado con esta enfermedad. Es un síndrome causado en la gran mayoría de los casos por la amplificación o mutación dinámica de las repeticiones del trinucleótido citosina-guanina-guanina (CGG) en la región promotora del gen FMR-1. La traducción de este gen da lugar a una proteína denominada FMRP. Se plantea que la ausencia o deficiencia de esta proteína ocasiona modificaciones de la actividad neuronal. Hoy día no hay cura para el síndrome frágil X, aunque se están desarrollando experimentos basados tanto en la terapia como la ingeniería genética, consistentes en reproducir la carencia de la proteína causante de la enfermedad. El tratamiento médico se limitará a reducir y palear todos los síntomas que pueden observarse en este síndrome. La temprana identificación del síndrome frágil X, resulta muy beneficiosa para los padres y la familia del paciente; pues reduce el impacto psicológico inicial y propicia que se apliquen programas de intervención precoz; proporcionando una mejor comprensión de la historia natural de la enfermedad y el estudio genético entre otros aspectos

          Translated abstract

          It was made a review of the Fragile X Syndrome, of which there were no reports in Cuba from the population point of view, until a psychopedagogical, social and clinico-genetic study of the persons with mental retardation was undertaken. 75 persons with defects of the FMR-1 gene, that is the gene related to this disease, were detected. It is a syndrome caused in most of the cases by the dynamic amplification or mutation of the repetitions of the cytosine-guanine-guanine (CGG) trinucleotide in the promoter region of the FMR-1gene. The translation of this gene gives rise to a protein denominated FMRP. It is stated that the absence or deficiency of this protein produces modifications of the neuronal activity. Today, there is no cure for the Fragile X Syndrome, eventhough experiments based on the therapy and genetic engineering are being developed to reproduce the lack of the protein causing the disease. The medical treatment will llimit itself to reduce and palliate all the symptoms that may be observed in this syndrome. The early identification of the Fragile X Syndrome is very benefitial for the parents and the family of the patient, since it diminishes the initial psychological impact and propitiates the implementation of early intervention programs, allowing a better comprehension of the natural history of the disease and the genetic study, among other aspects.

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          Most cited references50

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          Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in fragile X syndrome.

          Fragile X syndrome is the most frequent form of inherited mental retardation and is associated with a fragile site at Xq27.3. We identified human YAC clones that span fragile X site-induced translocation breakpoints coincident with the fragile X site. A gene (FMR-1) was identified within a four cosmid contig of YAC DNA that expresses a 4.8 kb message in human brain. Within a 7.4 kb EcoRI genomic fragment, containing FMR-1 exonic sequences distal to a CpG island previously shown to be hypermethylated in fragile X patients, is a fragile X site-induced breakpoint cluster region that exhibits length variation in fragile X chromosomes. This fragment contains a lengthy CGG repeat that is 250 bp distal of the CpG island and maps within a FMR-1 exon. Localization of the brain-expressed FMR-1 gene to this EcoRI fragment suggests the involvement of this gene in the phenotypic expression of the fragile X syndrome.
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            Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles.

            The CGG repeat in the 5' untranslated region of the fragile X mental retardation 1 gene (FMR1) exhibits remarkable instability upon transmission from mothers with premutation alleles. A collaboration of 13 laboratories in eight countries was established to examine four issues concerning FMR1 CGG-repeat instability among females with premutation (approximately 55-200 repeats) and intermediate (approximately 46-60 repeats) alleles. Our central findings were as follows: (1) The smallest premutation alleles that expanded to a full mutation (>200 repeats) in one generation contained 59 repeats; sequence analysis of the 59-repeat alleles from these two females revealed no AGG interruptions within the FMR1 CGG repeat. (2) When we corrected for ascertainment and recalculated the risks of expansion to a full mutation, we found that the risks for premutation alleles with <100 repeats were lower than those previously published. (3) When we examined the possible influence of sex of offspring on transmission of a full mutation-by analysis of 567 prenatal fragile X studies of 448 mothers with premutation and full-mutation alleles-we found no significant differences in the proportion of full-mutation alleles in male or female fetuses. (4) When we examined 136 transmissions of intermediate alleles from 92 mothers with no family history of fragile X, we found that, in contrast to the instability observed in families with fragile X, most (99/136 [72.8%]) transmissions of intermediate alleles were stable. The unstable transmissions (37/136 [27.2%]) in these families included both expansions and contractions in repeat size. The instability increased with the larger intermediate alleles (19% for 49-54 repeats, 30.9% for 55-59, and 80% for 60-65 repeats). These studies should allow improved risk assessments for genetic counseling of women with premutation or intermediate-size alleles.
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              A marker X chromosome.

              H Lubs (1969)
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                Author and article information

                Journal
                ibi
                Revista Cubana de Investigaciones Biomédicas
                Rev Cubana Invest Bioméd
                ECIMED (Ciudad de la Habana )
                1561-3011
                March 2007
                : 26
                : 1
                : 0
                Article
                S0864-03002007000100009
                3da321b6-afa1-4760-ab16-35fddab82ff8

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO Cuba

                Self URI (journal page): http://scielo.sld.cu/scielo.php?script=sci_serial&pid=0864-0300&lng=en
                Categories
                MEDICINE, RESEARCH & EXPERIMENTAL

                Medicine
                Fragile X Syndrome,FMRP protein,FMR-1 gene,mental retardation,Síndrome frágil X,proteína FMRP,gen FMR-1,retraso mental

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