Fragile X syndrome is the most common form of inherited mental retardation.

Fragile X happens when there is a change, or mutation, in a single gene called the Fragile X Mental Retardation 1 (FMR1) gene.  This gene normally makes a protein the body needs for the brain to develop.  But when there is a change in this gene, the body makes only a little bit or none of the protein, which can cause the symptoms of Fragile X.

Fragile X is inherited, which means it is passed down from parents to children.  Parents can have children with Fragile X even if the parents do not have Fragile X themselves.  The changes in the gene can become more serious when passed from parent to child. 

Some people may only have a small change in their FMR1 gene (called a premutation) and may not show any signs of Fragile X.  Other people may have bigger changes in the gene, called a full mutation, that cause the symptoms of Fragile X Syndrome.

For more information about genes and chromosomes, see Cells 101.

Not everyone with Fragile X has the same signs and symptoms, but they do have some things in common. Symptoms are often milder in girls than in boys.  Here are some common signs of Fragile X:

• Intelligence and learning – Many people with Fragile X have intellectual disabilities.  These problems can range from mild learning disabilities to more severe mental retardation. 
• Physical – Teens and adults with Fragile X may have long ears, faces, and jaws.  Many people with Fragile X may also have loose, flexible joints. They may have flat feet and be able to extend joints like the thumb, knee, and elbow further than normal.
• Social and Emotional – Most children with Fragile X have some behavior challenges.  They may be afraid or anxious in new situations.  Many children, especially boys, have trouble paying attention or may be aggressive.  Girls may be shy around new people.
• Speech and Language – Most boys with Fragile X have some problems with speech and language.  They may have trouble speaking clearly, or may stutter, or leave out parts of their words.  They may also have problems understanding “clues” when talking to other people, such as understanding the speaker’s tone of voice or that person’s body language.  Girls usually do not have severe problems with speech or language.
• Sensory – Many children with Fragile X are bothered by certain sensations, such as bright light, loud noises, or the way something feels.  Some do not like to be touched, or have trouble making eye contact with other people

For more specific information about symptoms, check out the What are the Signs and Symptoms of Fragile X Syndrome? section of the NICHD booklet Families and Fragile X Syndrome.

There is no cure for Fragile X, but there are ways to help with the symptoms.

People with Fragile X can get help to reduce or eliminate some of the learning, physical, social and emotional, speech and language, and sensory problems common in Fragile X.  The sooner those with Fragile X get help, the more they can learn and the better their outcomes.

For more specific information on treatments, check out the Are There Treatments for Fragile X Syndrome? section of the NICHD booklet Families and Fragile X Syndrome.