fragile X syndrome (or Martin-Bell syndrome or FRAX ) is a human genetic disorder caused by mutation of the FMR1 gene on the X chromosome, this mutation in a male on a female in 4000 and in 6000. About 1 in 256 women are carriers of the Fragile X and could pass it on to their children. About 1 in 800 males are carriers of Fragile X, and their daughters will, in turn, carry the gene. It contends with Down syndrome the record as the most common genetic cause of delay mentale.Normalmente the FMR1 gene contains between 6:53 codon CGG repeats (repeats of trinucleotides). In individuals with fragile X syndrome, the FMR1 allele has more than 230 repetitions of this codon. This causes the degree of expansion of cytosine methylation in the promoter of the FMR1 gene, resulting in silencing of the expression of FMR1 gene. Methylation of the FMR1 locus, which is located in chromosome band Xq27.3, at that point causes the constriction and the fragility of the X chromosome, a phenomenon which gives its name to sindrome.I males carrying a FMR1 gene with a significant expansion of the triplet CGG have symptoms of the disease, since you normally have only one copy of chromosome X. Females, however, have two copies of the X chromosome and therefore are twice as likely to have at least one functional allele. Women with an expanded FMR1 gene on one X chromosome may show some symptoms of the disease or be part normali.A mental retardation of varying degree from severe to moderate, some obvious features syndrome are the long face, large ears, large testicles (macrorchidismo), and low muscle tone. The behavioral characteristics may include stereotypic movements (eg, clapping) and atypical social development, particularly shyness and limited eye contact with the interlocutor. Some individuals with the fragile X syndrome are also included in the diagnostic criteria for autism. The mutation and methylation of the FMR1 gene results in the abolishment of the production of the protein for which the gene FMR1 coding, called FMRP (fragile X mental retardation protein) . FMRP is a protein-binding RNA (RNA-binding protein), expressed primarily in the testes and brain, the tissues most affected by syndrome. FMRP is associated with neuronal mRNAs encoding important proteins, and regulates certain key respects, such as transport to the synapse along the dendrites and its translation into proteins. In the absence of FMRP, many of the target protein messenger RNAs are deregulated and are well translated into protein. Similarly, new molecular functions of the protein, which regulate the stability of RNA messaggeri.Anche if there is still no cure for the syndrome, there is hope that a better understanding of its causes will lead to new therapies. At the time, the syndrome can be treated through behavioral therapy, special education, and when necessary, a treatment of anomalies individuals. We advise people who have relatives affected by fragile X syndrome to contact geneticists to assess the probability of having sick children, and to know the seriousness of the problems that may have descendants with the syndrome.
Federico Cesareo
