Merck Manual

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Fragile X Syndrome

By

Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Reviewed/Revised Nov 2023
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Fragile X syndrome is a genetic abnormality on the X chromosome that leads to intellectual disability and behavior problems.

The symptoms of Fragile X syndrome are caused by an abnormality of a specific gene on the X chromosome (see Gene Abnormalities Gene Abnormalities Chromosomes are structures within cells that contain a person's genes. Genes are segments of deoxyribonucleic acid ( DNA) and contain the code for a specific protein that functions in one or... read more ). People have an excessive number of copies (more than 200) of a small segment of deoxyribonucleic acid (DNA). People with 55 to 200 extra copies are considered to have a premutation because, although they do not have the disorder, their offspring are at greater risk of having it.

Symptoms of Fragile X Syndrome

Children and adults with the syndrome may have physical, intellectual, and behavior problems.

Physical features, which are often subtle, include delayed development; large, protruding ears; a prominent chin and forehead; and, in boys, large testes (most apparent after puberty).

Children may have mild to moderate intellectual disability. Features of autism Autism Spectrum Disorders Autism spectrum disorders are conditions in which people have difficulty developing normal social relationships, use language abnormally or not at all, and show restricted or repetitive behaviors... read more may develop, including repetitive speech and behavior, poor eye contact, and social anxiety.

Diagnosis of Fragile X Syndrome

  • DNA tests

The diagnosis of Fragile X syndrome is typically made when the child is school age or an adolescent. It is recommended that boys with autism and intellectual disability be tested for Fragile X syndrome, especially if their mother has relatives who have similar problems.

Treatment of Fragile X Syndrome

  • Speech, language, and occupational therapies

  • Sometimes medications

Early intervention, including speech and language therapies and occupational therapy, can help children with Fragile X syndrome maximize their abilities.

Stimulants, antidepressants, and antianxiety medications may be beneficial for some children.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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