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Nature of the Genetic Difficulty

Fragile X Syndrome, known as a FXS, is caused by changes in the fragile X mental retardation 1 (FMR1) gene found on the X chromosome. The FMR1 gene is responsible for the fragile X mental retardation protein (FMRP), which is needed for normal brain development. People who have FXS cannot make this protein. People who have other fragile X-associated disorders have changes in their FMR1 gene but usually make some of the protein.

There is a place in the FMR1 gene where the nucleotides CGG is repeated over and over again. In most people, the number of repeats is small (6 to 45 repeats), which is normal. If the number of repeats is too large (more than 200 repeats), the gene turns off. When the gene is turned off, no protein is made. Without the protein, the person develops FXS. This is called a "trinucleotide repeat disorder."

FXS affects both males and females. However, females often have milder symptoms than males. The exact number of people who have FXS is unknown, but it has been estimated that about 1 in 5,000 males are born with the disorder.

Basis Facts of Disease

Physical features that affect some, but not all, FXS patients include:

  • A large head;
  • A long face; and
  • Prominent ears, chin, and forehead.

Other signs that a child might have FXS include:
  • Developmental delays (not sitting, walking, or talking at the same time as other children the same age);
  • Learning disabilities (trouble learning new skills); and
  • Social and behavior problems (such as not making eye contact, anxiety, trouble paying attention, hand flapping, acting and speaking without thinking, and being very active).

FXS patients may also exhibit hyperactivitiveness, mental retardation, lack of attention, intellectual disability, repetition of activities and other emotional, social and behavioral problems. The symptoms of learning disability may range from mild learning problem to severe intellectual disorders. Other signs and symptoms include abnormality in sensory, social and emotional behavior. Males who have Fragile X Syndrome usually have some degree of intellectual disability that can range from mild to severe. Females with FXS can have normal intelligence or some degree of intellectual disability with or without learning disabilities.


There is no cure for FXS. However, the outlook for children with fragile X syndrome is better when the disease is diagnosed early. Among people with a full fragile X mutation, approximately half of females and almost all males have lifelong mental retardation. Treatment services can help people learn important skills and therapies include learning to learn to talk, walk, and interact with others. In addition, medicine can be used to help control some issues, such as behavior problems. People with fragile X syndrome typically have a normal lifespan.

Sources Cited

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