Fragile X Syndrome
What is it?
Fragile X syndrome is a form of mental retardation caused by a mutated gene on the X chromosome. It is called fragile X syndrome because the long arm of the X-shaped chromosome looks like it might break
off.
Who gets it?
Fragile X syndrome is the most common form of inherited mental retardation. The symptoms of fragile X syndrome are more severe in boys than in
girls.
What causes it?
Fragile X syndrome is caused by a mutation in the FMR-1 (Fragile X Mental Retardation) gene, located on the X chromosome. In very simple terms, genes determine our genetic makeup, such as how we look. Chromosomes are thread-like structures that carry genes and help to pass on genetic information. The X chromosome is one of two chromosomes that determine an individual's sex. Males have an X and a Y chromosome, while females have two X chromosomes. When a gene mutates, it undergoes a sudden structural change that results in a new characteristic or trait not originally found in the parent gene. The FMR-1 gene appears to play a role in early development, so it causes developmental delays in its mutated form. However, this gene appears to be able to exist in what researchers call a pre-mutated form for several generations of a family. With each generation, the gene becomes closer to full mutation until it results in fragile X syndrome. Boys are more likely to develop more severe symptoms of fragile X because they have only one copy of the X chromosome. Because girls have two X chromosomes, the abnormal gene on one X chromosome might be balanced by a normal gene on the other X chromosome. However, this girl would be a carrier for fragile X. Each of her children would have a 50 percent chance of inheriting her fragile X
gene.
What are the symptoms?
Symptoms of fragile X syndrome differ among boys and girls. Boys with fragile X appear normal atbirth. However, developmental delays become apparent as they grow older. They may also have behavioral problems such as hyperactivity and attention deficit disorder (ADHD). Most boys (as high as 90%) with fragile X syndrome show mild to severe mental retardation. Common physical traits include large, protruding ears; a long, narrow face with a prominent chin and forehead; double-jointed fingers; flat feet; puffy eyelids; and enlarged testes after puberty. Because they have a second normal X chromosome, only 30 to 50% of girls with a full FMR-1 gene mutation develop symptoms.
Symptoms can range from mild learning disabilities to mental retardation, and can include behavioral problems. The physical traits seen in boys are usually not as obvious in girls. In terms of speech, children with fragile X may speak in sudden, rapid bursts of words or repeat words. Males with Fragile X may get stuck on one topic, and talk about that one thing constantly. In a learning environment, girls with fragile X may have difficulty with math, but do very well in reading and spelling. Males with fragile X need to see the whole in order to understand the parts. Both boys and girls with fragile X syndrome experience frequent ear and sinus infections, as well as digestive disorders. Vision problems, including nearsightedness and lazy eye, also occur frequently. Some children with fragile X may have seizures. Children with fragile X are extremely hypersensitive to their environment. This makes it difficult for them to screen out external factors such as noise, lights, or odors. These types of stimuli can cause emotional outbursts or tantrums. While males with fragile X tend to be extremely friendly and sociable, other fragile X behaviors are similar to autism. These include difficulty maintaining eye contact, hand flapping, hand biting, and a dislike of being touched. While fragile X children have a normal lifespan, around 50% of them will develop a heart condition called mitral valve prolapse during
adulthood.
How is it diagnosed?
Fragile X syndrome is diagnosed based upon developmental delays, behavioral characteristics, and physical traits. Your doctor will ask about any family history of mental retardation. To make a definite diagnosis, a drop of blood taken from a finger can be analyzed for the fragile X gene. If a woman is pregnant and she is a carrier, or there is a history of fragile X syndrome in the family, there are procedures that can be performed during the pregnancy to screen for fragile X syndrome. With amniocentesis, a long thin needle is inserted through the woman's abdomen and a sample of amniotic fluid is removed. This procedure can be performed in the 15th to 18th weeks of pregnancy. Chorionic villus sampling is a procedure performed in the 10th to 12th week of a pregnancy. A needle is inserted into the placenta to remove a small amount fetal tissue for study. Another technique is called percutaneous umbilical blood sampling, performed at the 18th to 22nd weeks of pregnancy. This procedure is also known as cordocentesis, and involves inserting a needle through the pregnant woman's abdomen and into a blood vessel in the umbilical cord. A blood sample is drawn through the cord. However, keep in mind that the presence of the fragile X chromosome does not necessarily mean the child will have any symptoms of the
disorder.
What is the treatment?
Although there is currently no cure for fragile X syndrome, it can be treated through a combination of speech and language therapy, occupational therapy, physical therapy, and psychotherapy, depending upon the child's symptoms. Drugs may be used to treat behavioral problems, such as mood swings and aggressive outbursts. Your child's therapists can also teach you techniques for reducing these problems. Anticonvulsants that are used to treat seizures can also help with behavioral problems. Generally, children with fragile X benefit from following a regular routine and avoiding over-stimulation. Try to keep distractions, such as noise and odors, to a minimum.
Self-care tips
There is no known way to prevent fragile X syndrome. However, with help from their parents, healthcare providers, and educators, these children can function in society and in a learning environment. If your child has fragile X syndrome, learn all you can about this disorder, and seek support from your healthcare provider, family, and community.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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