Hunter JE, Berry-Kravis E, Hipp H, Todd PK.Tassone F, Gantois I, Sonenberg N, Mandel JL, Hagerman PJ. Hagerman RJ, Berry-Kravis E, Hazlett HC, Bailey DB Jr, Moine H, Kooy RF,.Cornish KM, Turk J, Wilding J, Sudhalter V, Munir F, Kooy F, Hagerman R.Īnnotation: Deconstructing the attention deficit in fragile X syndrome: aĭevelopmental neuropsychological approach.Their sons receive a Y chromosome, which does not include the FMR1 gene. Men pass the premutation only to their daughters. By contrast, the premutation in men does not expand to more than 200 repeats as it is passed to the next generation. This means that women with the premutation have an increased risk of having a child with fragile X syndrome. In women, the FMR1 gene premutation on the X chromosome can expand to more than 200 CGG repeats in cells that develop into eggs. In most cases, males experience more severe symptoms of the disorder than females. In males (who have only one X chromosome), a mutation in the only copy of a gene in each cell causes the disorder. X-linked dominant means that in females (who have two X chromosomes), a mutation in one of the two copies of a gene in each cell is sufficient to cause the disorder. (The Y chromosome is the other sex chromosome.) The inheritance is dominant if one copy of the altered gene in each cell is sufficient to cause the condition. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. The premutation is also associated with an increased risk of disorders called fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS).įragile X syndrome is inherited in an X-linked dominant pattern. Some children with an FMR1 premutation may have learning disabilities or autistic-like behavior. As a result, they may have mild versions of the physical features seen in fragile X syndrome (such as prominent ears) and may experience emotional problems such as anxiety or depression. In some cases, however, individuals with a premutation have lower than normal amounts of FMRP. Most people with this premutation are intellectually normal. Males and females with 55 to 200 repeats of the CGG segment are said to have an FMR1 gene premutation. Loss or a shortage (deficiency) of this protein disrupts nervous system functions and leads to the signs and symptoms of fragile X syndrome. The abnormally expanded CGG segment turns off (silences) the FMR1 gene, which prevents the gene from producing FMRP. In people with fragile X syndrome, however, the CGG segment is repeated more than 200 times. Normally, this DNA segment is repeated from 5 to about 40 times. Nearly all cases of fragile X syndrome are caused by a mutation in which a DNA segment, known as the CGG triplet repeat, is expanded within the FMR1 gene. Synapses are critical for relaying nerve impulses. This protein helps regulate the production of other proteins and plays a role in the development of synapses, which are specialized connections between nerve cells. The FMR1 gene provides instructions for making a protein called FMRP. Mutations in the FMR1 gene cause fragile X syndrome. These features include a long and narrow face, large ears, a prominent jaw and forehead, unusually flexible fingers, flat feet, and in males, enlarged testicles (macroorchidism) after puberty. Most males and about half of females with fragile X syndrome have characteristic physical features that become more apparent with age. Seizures occur in about 15 percent of males and about 5 percent of females with fragile X syndrome. About one-third of individuals with fragile X syndrome have features of autism spectrum disorder that affect communication and social interaction. They may have attention deficit disorder (ADD), which includes an impaired ability to maintain attention and difficulty focusing on specific tasks. Children with fragile X syndrome may also have anxiety and hyperactive behavior such as fidgeting or impulsive actions. Most males with fragile X syndrome have mild to moderate intellectual disability, while about one-third of affected females are intellectually disabled. Usually, males are more severely affected by this disorder than females.Īffected individuals usually have delayed development of speech and language by age 2.
Fragile X syndrome is a genetic condition that causes a range of developmental problems including learning disabilities and cognitive impairment.
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