Definition of Fragile X syndrome:

Fragile X syndrome is a genetic condition involving changes in part of the X chromosome. It is the most common form of inherited intellectual disability (mental retardation) in boys.

Causes, incidence, and risk factors:

Fragile X syndrome is caused by a change in a gene called FMR1. A small part of the gene code is repeated on a fragile area of the X chromosome. The more repeats, the more likely there is to be a problem

The FMR1 gene makes a protein needed for your brain to grow properly. A defect in the gene makes your body produce too little of the protein, or none at all.

Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely. You can have Fragile X syndrome even if your parents do not have it.

Symptoms:

• Delay in crawling, walking, or twisting
• Hand clapping or hand biting
• Hyperactive or impulsive behavior
• Mental retardation
• Speech and language delay
• Tendency to avoid eye contact

Physical signs may include:

• Flat feet
• Flexible joints and low muscle tone
• Large body size
• Large forehead or ears with a prominent jaw
• Long face
• Soft skin

Some of these problems are present at birth, while others may not develop until after puberty.

Family members who have fewer repeats in the FMR1 gene may not have mental retardation, but may have other problems. Women with less severe changes may have premature menopause or difficulty becoming pregnant. Both men and women may have problems with tremors and poor coordination.

Signs and tests:

There are very few outward signs of Fragile X syndrome in babies. Some signs may include:

• Large head circumference in babies
• Mental retardation
• Large testicles after the start of puberty
• Subtle differences in face features

In females, excess shyness may be the only sign of the disorder.

Genetic testing can diagnose this disease.

Treatment:

There is no specific treatment for Fragile X syndrome. Specialized training and education help affected children function at as high a level as possible.

Support Groups:

National Fragile X Foundation -- www.nfxf.org

Expectations (prognosis):

How well the patient does depends on the amount of intellectual disability (mental retardation).

Complications:

Complications vary depending on the type and severity of symptoms.

• Recurrent infections in children
• Seizure disorder

Fragile X syndrome can be a cause of autism or related disorders, although not all children with fragile X syndrome have these conditions.

Prevention:

Genetic counseling may be helpful if you have a family history of this syndrome and are planning to become pregnant.