Fragile X Syndrome

Written by Jacquelyn Cafasso
Medically Reviewed by Jennifer Wider, MD

What Is Fragile X Syndrome?

Fragile X syndrome is an inherited genetic disease that causes intellectual and developmental disabilities. Inherited means that the disease is passed down from parents to children through their genes. Fragile X syndrome is the most common hereditary source of mental disability in boys. People with fragile X syndrome usually experience a range of developmental and learning problems. The disease is a life-long condition. Only some people with fragile X syndrome are able to live independently.

According to the Genetics Home Reference (GHR), fragile X syndrome is found in about one in every 4,000 males and about one in every 8,000 females. (GHR) Males usually have more severe symptoms than females.

What Causes Fragile X Syndrome?

Fragile X syndrome is caused by a defect in the FMR1 gene located on the X chromosome. The X chromosome is one of two types of sex chromosomes. The other is the Y chromosome. Women have two X chromosomes while men have one X chromosome and one Y chromosome.

The defect (mutation) on the FMR1 gene prevents the gene from properly making a protein called the fragile X mental retardation 1 protein. This protein plays a role in the functioning of the nervous system. The exact function of the protein is not fully understood. A lack or shortage of this protein causes the symptoms characteristic of fragile X syndrome.

What Are the Symptoms of Fragile X Syndrome?

Fragile X syndrome results in learning disabilities, developmental delays, and social or behavioral problems. Disabilities vary in severity. Male patients usually have some level of intellectual disability. Female patients may have some intellectual disability or learning disability or both, but many women with fragile X syndrome will have normal intelligence. These women might only be diagnosed with fragile X syndrome if another family member is also diagnosed.

People with fragile X syndrome may show a combination of the following signs as children and throughout life:

  • developmental delays, such as taking longer than normal to learn to sit, walk, or talk compared with other children of the same age
  • stuttering
  • intellectual and learning disabilities, such as having trouble learning new skills or information
  • anxiety (general or social)
  • autism
  • impulsiveness
  • attention problems
  • social problems, such as not making eye contact with other people, disliking being touched, and trouble understanding body language
  • hyperactivity
  • seizures
  • depression
  • difficulty sleeping

Some people with fragile X syndrome have facial or other physical abnormalities. These may include:

  • a large forehead or ears with a prominent jaw
  • an elongated face
  • protruding ears, forehead, and chin
  • loose or flexible joints
  • flat feet

How Is Fragile X Syndrome Diagnosed?

Children who show signs of developmental delays or other outward signs including a large head circumference, or subtle differences in facial features at a young age may be tested for fragile X syndrome. Fragile X syndrome can be diagnosed using a DNA blood test called the FMR1 DNA Test. The test looks for changes in the FMR1 gene that are associated with fragile X syndrome.

How Is Fragile X Syndrome Treated?

Fragile X syndrome cannot be cured. Treatment is aimed at helping the patient learn key skills, such as language use and proper social interaction. This may involve receiving extra help from teachers, therapists, family members, doctors, and coaches.

There may be services and other resources available in your community to help children learn important skills for proper development. Contact the National Fragile X Foundation at 1-(800) 688-8765 for more information regarding specialized therapy and educational plans.

Medications that are typically prescribed for behavior disorders, such as attention deficit disorder (ADD) or anxiety, may also be prescribed to treat the symptoms of fragile X.

What Can Be Expected in the Long Term?

Fragile X syndrome is a life-long condition and can affect all aspects of life, including one’s schooling, work, and social life.

According to the Centers for Disease Control and Prevention (CDC), about 44 percent of women and nine percent of men with fragile X syndrome reach a high level of independence as adults. The majority of women achieved at least a high school diploma and about half succeeded in holding a full-time job. (CDC)

However, the majority of men with fragile X syndrome require assistance with daily activities as adults. Few male patients achieve a high-school diploma or succeed in finding full-time work.

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