Fragile X syndrome is a genetic abnormality on the X chromosome that leads to intellectual disability and behavior problems.
Chromosomes are structures within cells that contain DNA and many genes. Genes are segments of deoxyribonucleic acid (DNA) and contain the code for a specific protein that functions in one or more types of cells in the body. Genes contain instructions that determine how the body looks and functions. (See Genes and Chromosomes for a discussion about genetics.)
Fragile X syndrome is the most commonly diagnosed inherited cause of intellectual disability, and boys are affected more often than girls. Fragile X syndrome is second only to Down syndrome as a cause of intellectual disability in boys. However, unlike Fragile X syndrome, Down syndrome is not inherited in most cases. (For more information, see the National Fragile X Foundation.)
The symptoms of Fragile X syndrome are caused by an abnormality of a specific gene on the X chromosome (see Gene Abnormalities). 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).
The joints may be abnormally flexible, and heart disease (mitral valve prolapse) may occur.
Children may have mild to moderate intellectual disability. Features of autism may develop, including repetitive speech and behavior, poor eye contact, and social anxiety.
Women who have the premutation may go through menopause at a much younger age, sometimes in the mid-30s.
People who have the premutation are at risk of Fragile X–associated tremor/ataxia syndrome (FXTAS), which causes tremor, loss of coordination, later intellectual disability, and, over time, deterioration of cognitive function.
Diagnosis of Fragile X Syndrome
DNA tests
Fragile X syndrome can be detected by DNA tests done after birth. (See also Next-generation sequencing technologies.)
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.
National Fragile X Foundation: Provides advocacy, education, support, and public and professional awareness programs and services
