{"id":2512,"date":"2026-07-15T15:10:35","date_gmt":"2026-07-15T15:10:35","guid":{"rendered":"https:\/\/genolifeadn.com\/?p=2512"},"modified":"2026-07-15T18:20:21","modified_gmt":"2026-07-15T18:20:21","slug":"que-es-el-sindrome-x-fragil","status":"publish","type":"post","link":"https:\/\/genolifeadn.com\/en\/que-es-el-sindrome-x-fragil\/","title":{"rendered":"What is Fragile X syndrome?"},"content":{"rendered":"
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What is Fragile X syndrome?<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t

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Fragile X syndrome<\/em>\u00a0(FXS) is the most common hereditary cause of intellectual disability, affecting approximately 1 in every 4,000 males. In the vast majority of cases, this X-linked disorder is caused by CGG repeats in the 5\u2032 untranslated region (UTR) of the FMR1 gene.
The alleles that cause FXS, or complete mutations, contain 200 or more copies of the repeat that are hypermethylated and transcriptionally silenced. The unstable alleles that give rise to complete mutations are called premutations and are associated with phenotypes distinct from FXS. The mutational mechanism, combined with the location of this gene on the X chromosome, leads to distinctive inheritance patterns in which the relevant alleles are passed from intellectually normal males to their unaffected daughters and then to their affected sons.
FXS may be suspected in both sexes and involves a variable clinical phenotype. Individuals with FXS may present with a range of symptoms, from learning difficulties and a normal IQ to severe intellectual disability and autistic behaviors. Physical characteristics have been described, but they are often nonspecific. Thus, diagnosis is based on the detection of mutations in the FMR1 gene.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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The physical characteristics of FXS are quite subtle, and the first clinical sign is usually developmental delay, mild motor delays, and\/or speech delays. Autistic-like behaviors may be observed, such as hand flapping, poor eye contact, and hand biting.<\/p>\n

The average IQ among adult men with the fully methylated mutation is approximately. Men who are less severely affected typically have incomplete methylation, which results in incomplete activation of\u00a0FMR1<\/em>, and may even have an IQ at the borderline or in the low-normal range. In general, for FXS, cognitive deficits include problems with working and short-term memory, executive function, and mathematical and visuospatial skills.\u00a0Because the disorder is X-linked, women are generally affected much less severely than men, particularly in terms of cognitive functioning, but they tend to have a higher risk of emotional problems compared to the general population. Women with the full mutation usually have a normal or borderline IQ, and most will have associated learning disabilities and\/or emotional problems.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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People with FXS generally do not have significant medical problems. Recurrent otitis media and recurrent sinusitis are common during childhood. There may be joint laxity with hyperextensibility in the finger joints and flat feet, which usually improves with age. Gastroesophageal reflux disease occurs in one-third of young infants with FXS and may present with irritability or recurrent vomiting. Seizures and epilepsy are another common feature of FXS during childhood, with an incidence of 13\u201318 % in boys and 5 % in girls.<\/p>\n

Most people with the premutation have normal intelligence, but men are prone to attention problems, executive dysfunction, social deficits, and obsessive-compulsive behavior. Approximately 20 % of women with an FMR1 premutation have premature ovarian failure (POF), which is the premature cessation of menstruation before age 40.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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