Martin-Bell syndrome; Marker X syndrome
Fragile X syndrome is a genetic condition involving changes in part of the X chromosome. It is the most common form of inherited intellectual disability in boys.
Fragile X syndrome is caused by a change in a gene called FMR1. A small part of the gene code is repeated several times in one area of the X chromosome. The more repeats, the more likely the condition will occur.
The FMR1 gene makes a protein needed for your brain to function properly. A defect in the gene makes your body produce too little of the protein, or none at all.
Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X expansion is likely to affect them more severely. You can have fragile X syndrome even if your parents do not have it.
A family history of fragile X syndrome, developmental problems, or intellectual disability may not be present.
Behavior problems associated with fragile X syndrome include:
Physical signs may include:
Some of these problems are present at birth, while others may not develop until after puberty.
Family members who have fewer repeats in the FMR1 gene may not have intellectual disability. Women may have premature menopause or difficulty becoming pregnant. Both men and women may have problems with tremors and poor coordination.
There are very few outward signs of fragile X syndrome in babies. Some things the health care provider may look for include:
In females, excess shyness may be the only sign of the disorder.
Genetic testing can diagnose this disease.
There is no specific treatment for fragile X syndrome. Instead, training and education have been developed to help affected children function at the highest possible level. Clinical trials are ongoing (www.clinicaltrials.gov) and looking at several possible medicines for treating fragile X syndrome.
National Fragile X Foundation: fragilex.org
How well the person does depends on the amount of intellectual disability.
Complications vary, depending on the type and severity of symptoms. They may include:
Fragile X syndrome can be a cause of autism or related disorders, although not all children with fragile X syndrome have these conditions.
Genetic counseling may be helpful if you have a family history of this syndrome and are planning to become pregnant.
Hunter JE, Berry-Kravis E, Hipp H, Todd PK. FMR1 disorders. GeneReviews. 2012:4. PMID: 20301558 pubmed.ncbi.nlm.nih.gov/20301558/. Updated November 21, 2019.
Kumar V, Abbas AK, Aster JC. Genetic and pediatric diseases. In: Kumar V, Abbas AK, Aster JC, eds. Robbins Basic Pathology. 10th ed. Philadelphia, PA: Elsevier; 2018:chap 7.
Madan-Khetarpal S, Arnold G. Genetic disorders and dysmorphic conditions. In: Zitelli BJ, McIntire SC, Nowalk AJ, eds. Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 1.BACK TO TOP
Review Date: 7/29/2019
Reviewed By: Anna C. Edens Hurst, MD, MS, Assistant Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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