Fragile X Syndrome

Fragile X Syndrome: Description, Causes and Risk Factors: Fragile X SyndromeFragile X is caused by a defect in a single gene. This gene, called FMR1 for “Fragile X Mental Retardation - 1” or FRAXA. The FMR1 gene is located on the long arm of the X chromosome. At the start of this gene lies a region of DNA which varies in length from one person to another. Ordinarily, this stretch of DNA falls within a range of length that would be considered "normal." In some people, however, this stretch of DNA is somewhat longer; this gene change is called a "premutation". Although a person who carries the premutation does not typically have symptoms of Fragile X, the stretch of DNA is prone to further expansion when it is passed from a woman to her children. When the stretch of DNA expands beyond a certain length, the gene is switched off and does not produce the protein that it is normally makes. This gene change is called a "full mutation." The FMR protein's normal role is to help shape the connections between neurons (brain cells) that underlie learning and memory, and we are beginning to understand how the lack of the protein causes Fragile X syndrome. Because absence of the FMR protein delays the development of neurons, rather than damaging or destroying them, it is likely that treatments now being investigated will benefit all individuals with Fragile X, regardless of age. A male who inherits a full mutation exhibits Fragile X syndrome because his only X chromosome contains the mutated gene. A female may not be as severely affected because each cell of her body needs to use only one of its two X chromosomes and randomly inactivates the other. In people with Fragile X, a defect in FMR1 (a "full mutation") shuts the gene down. Like a defective factory, FMR1 cannot manufacture the protein that it normally makes. Other individuals are carriers: they have a small mutation in FMR1 (called a "premutation"). Carriers do not show symptoms of Fragile X syndrome, but they may be at risk for related disorders such as Fragile X-associated tremor/ataxia syndrome (FXTAS) and primary ovarian insufficiency. Fragile X is inherited. Carrier men pass the premutation to all their daughters but none of their sons. Each child of a carrier woman has a 50% chance of inheriting the mutated gene. The Fragile X premutation can be passed silently down through generations in a family before a child is born with the syndrome. Fragile X syndrome is the most common inherited cause of intellectual disabilities and the most common known cause of autism. Fragile X affects 1 in 4000 males and 1 in 6000 females of all races and ethnic groups. About 30% of boys with fragile X meet full criteria for autism. Most boys and some girls have some symptoms of autism, but many tend to be very social and interested in other people. Symptoms: Physical Features: Long face, large ears, flat feet. Other Symptoms: Intellectual disabilities, ranging from mild learning disabilities to mental retardation.
  • Attention deficit and hyperactivity, particularly in young children.
  • Anxiety and unstable mood.
  • Autistic behaviors.
  • Emotional and behavioral problems are common in both sexes.
  • Sensory integration problems, such as hypersensitivity to loud noises or bright lights.
  • Speech delay, with expressive language more severely affected than receptive language.
  • Seizures (epilepsy) affect about 25% of people with Fragile X.
Diagnosis: This blood test, developed in 1992, is accurate and can detect both carriers and fully-affected individuals. It can be ordered by any physician; the blood sample is then sent to a lab that offers the test. It usually takes several weeks to get the results. Treatment: There is currently no cure for Fragile X, although appropriate education and medications can help maximize the potential of each child. However, most boys and many girls remain significantly affected throughout their lives. The cost to society for treatment, special education, and lost income is staggering. The need for research aimed at treatment is urgent. NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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