Fragile X Syndrome

Here you’ll find answers to some of the questions that parents often have about this condition. Additional resources are listed at the bottom of the page. Diagnosis and management information can be found in the Fragile X Syndrome module, which is written for primary care clinicians but also may be of help to parents and family members.

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disabilities and a common known cause of autism. It may not be immediately apparent that a person has fragile X syndrome as symptoms, such as learning problems, autism, and anxiety, and some physical features, can be subtle.

Males are usually more affected than females. Features may include: intellectual disabilities, ranging from mild learning disabilities to intellectual disability, attention deficit and hyperactivity, anxiety and unstable mood, autistic behaviors and/or sensory integration problems, such as hypersensitivity to loud noices or bright lights, speech delay, with expressive language more severely affected than receptive language, and seizures. Physical features are usually hard to recognize in babies and young children, but sometimes become more apparent with age: long face, large ears, flat feet, hyperextensible joints, low muscle tone, and in adult men, large testes.

Testing for fragile X is done by a simple and reliable DNA blood test. This test is widely available, so talk with your doctor.

Prognosis will depend on your child's symptoms now. Children who are mildly affected at diagnosis may be less affected as adults than children with severe symptoms at diagnosis.

Fragile X syndrome occurs when there is an expansion of the genetic material in a specific place on the X chromosome. The chances of having a second child with fragile X increase if the mother has a larger expansion, and can be as high as 50% if the second child is male. This should be discussed with your doctor as the risks can be better estimated with more information about the mother's genetic material. Prenatal testing for fragile X is available.

There is currently no cure for fragile X, although appropriate education and medications can help maximize the potential of each child. However, most boys and many girls remain significantly affected throughout their lives.

Only about 20% of children with fragile X syndrome exhibit significant autistic behaviors, so it is very possible for a child to have fragile X syndrome and not have autism. Autistic behaviors include poor eye contact, hand-flapping, self-injurious behavior, and poor sensory skills.

Extended family members of individuals with fragile X syndrome may have related disorders, including social problems, learning disabilities, premature ovarian failure, and fragile X-associated trem/ataxia syndrome, depending on gene status. Screening is sometimes done on extended family members to provide proactive care for problems that may arise as well as to give genetic counselors more information so that they may better counsel a family regarding recurrence risk.