Fragile X Syndrome and Associated Disorders

Fragile X syndrome and fragile X-associated disorders are a group of genetic conditions that can affect individuals and their families in many ways. Find out more about fragile X syndrome and fragile X-associated disorders.

What are fragile X-associated disorders?

All fragile X-associated disorders are caused by changes in the same gene, the fragile X mental retardation 1 (FMR1) gene. Fragile X-associated disorders include:

• Fragile X syndrome, the most common known cause of intellectual disability that can be inherited.
• Fragile X-associated primary ovarian insufficiency (FXPOI), a cause of infertility and early menopause among adult women.
• Fragile X-associated tremor/ataxia syndrome (FXTAS), a cause of tremors and problems with walking, balance, and memory among older adults.

FXTAS and FXPOI recently were discovered by studying families affected by fragile X syndrome. Hence, more is known about fragile X syndrome than about FXPOI or FXTAS.

What are the signs of fragile X syndrome?

Some, but not all, children with fragile X syndrome have facial features that may become more noticeable with age. These features include:

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

Other signs that a child might have fragile X syndrome include:

• Developmental delays (not sitting, walking, or talking as early as other developing children);
• Learning disabilities (poor achievement in school);
• Social and behavioral problems (such as poor eye contact, increased anxiety, decreased attention, hand flapping, impulsive behaviors, and hyperactivity); and
• Seizures.

Males who have fragile X syndrome usually have some degree of intellectual disability that can range from mild to severe. Females with fragile X syndrome can have normal intelligence or some degree of intellectual disability.

How many people have fragile X syndrome?

The exact number of people who have fragile X syndrome is unknown, but it is estimated that about 1 in 4,000 males and 1 in 6,000 to 8,000 females have the disorder. Although fragile X syndrome occurs among both males and females, females usually have milder symptoms.

What causes fragile X syndrome?

Fragile X syndrome is caused by a mutation (change) in the FMR1 gene located on the sex chromosome X (males have only one X chromosome and females have two). The FMR1 gene usually makes a protein that is needed for normal brain development. Among individuals who have fragile X syndrome, the mutated gene does not make this protein.

Watch a video about what causes fragile X syndrome [VIDEO - 3.20 MB] (Note: If you have difficulty viewing the clip, please send us an email.) or download a transcript.

How is fragile X syndrome diagnosed?

Fragile X syndrome can be diagnosed by testing a person's DNA from a blood sample. A physician or genetic counselor must order the test. Testing also can be done to detect changes in the FMR1 gene that can lead to FXTAS or FXPOI.

A diagnosis of fragile X syndrome can be beneficial to the family because it can provide an explanation for a child's intellectual disabilities and behavioral problems. This allows the family and other caregivers to learn more about the disorder and manage care so that the child can reach his or her full potential.

What is CDC doing about fragile X syndrome and fragile X-associated disorders?

CDC and its partners have been working on several public health activities to learn more about fragile X syndrome and to improve the health and well-being of people who have fragile X-associated disorders.

These projects include:

• Fragile X Clinical and Research Consortium
  The Fragile X Clinical and Research Consortium is promoting the health and well-being of people who have fragile X syndrome by learning more about how fragile X syndrome affects people and families. More than 20 fragile X clinics across the United States are involved in the consortium. The goals of the consortium include making a fragile X patient registry, standardizing and ensuring appropriate care for people affected by fragile X syndrome, and collecting information over time about people living with fragile X syndrome. This information will be used to determine the public health needs of people with fragile X syndrome and ensure that the public health needs of people with fragile X syndrome are met.
• National Fragile X Family Survey
  CDC is working with researchers from the University of North Carolina at Chapel Hill and RTI International on a national survey of families with fragile X syndrome and fragile X-associated disorders. This survey will address many aspects of fragile X syndrome and fragile X-associated disorders, including diagnosis, treatments and services, family support and communication, adult needs and transition to adulthood, and key public health outcomes. The results from this survey will be used to find better ways of serving individuals and families affected by fragile X.
• Prevalence of the Fragile X Premutation Study
  CDC is supporting a study to determine the prevalence of the fragile X premutation. The study covers diverse aspects of participants' lives, including intergenerational relationships, family functioning, physical and mental health, and well-being from late adolescence through late life. The study offers a unique opportunity to study the prevalence of fragile X-associated disorders among a large sample group and to explore the lives of people with fragile X-associated disorders.

More Information

• Fragile X syndrome
• Health problems among fragile X carriers
• Additional resources
  • The National Fragile X Foundation
  • FRAXA Research Foundation