Fragile X Syndrome

Cause of inherited mental retardation

Fragile X syndrome is caused by a genetic defect of a single gene on the X (female) chromosome. Fragile X syndrome affects approximately 1 in 4,000 males and 1 in 8,000 females. Women have two X chromosomes, and a normal X chromosome may mitigate the effects of a defective X chromosome. Fragile X syndrome affects people of all ethnic backgrounds. It is the most common cause of inherited mental retardation.

Symptoms
The effects of Fragile X on an individual's mental status are partially related to the environment in which the individuals grows up, what educational and therapeutic opportunities are available, and how early those interventions are begun. The cognitive and neuropsychological symptoms include:

• Mild to severe mental retardation (IQ 20-80)
• Poor eye contact, hand biting, or hand flapping behaviors are present in 16-25% of individuals. Some children with Fragile X syndrome may also be diagnosed with autism, and some children with autism may have undiagnosed Fragile X syndrome.
• Attention deficits, and in about 1/3 of males, aggression
• Approximately 20% of individuals have a seizure disorder

Some musculoskeletal problems such as scoliosis may be present. Adolescents and adults with Fragile X syndrome have a long thin face with prominent ears, forehead, and jaw. A defect in the mitral valve of the heart may also occur.

Diagnosis
Fragile X syndrome is difficult to diagnose in children. An affected infant may develop normally at first. After age one year, though, the child begins to have noticeable delays in language and short-term memory. Physical signs of Fragile X, such as the typical facial features, are only noticeable after the onset of puberty.

Fragile X syndrome may be suspected if the individual has a number of male relatives with mental retardation. However, in many families the child with Fragile X syndrome is the first member known to have mental retardation. If Fragile X syndrome is suspected, a blood test known as FMR1/DNA is used to confirm the diagnosis.

Treatment
Medical care for an individual with Fragile X syndrome focuses on treating common problems and helping the individual achieve his/her developmental potential. Screenings for scoliosis, heart valve defects, and vision problems will be performed. A comprehensive developmental evaluation by a speech/language pathologist, occupational therapist, and physical therapist may be performed several times during an individual's life to help promote independent living. Children affected by Fragile X will benefit from educational support services and behavior management. Fragile X does not shorten a person's life span.

Last updated 11/20/05

Information for this article was taken from:
- Jewell, J. (2003). Fragile X syndrome. eMedicine, accessed at http://www.emedicine.com/ped/topic800.htm
- National Fragile X Foundation