Fragile X syndrome

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Fragile X syndrome is a genetic condition involving changes in part of the X chromosome. It is the most common form of inherited mental retardation in males and a significant cause of mental retardation in females.

Martin-Bell syndrome; Marker X syndrome

Fragile X syndrome is caused by a change in the FMR1 gene. A small section of the gene code (three letters only -- CGG) is repeated on a fragile area of the X chromosome. The more repeats, the more likely there is to be a problem.

Normally, the FMR1 gene makes a protein needed for your brain to grow properly. A defect in this gene makes your body produce too little of the protein, or none at all.

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Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely. You can have Fragile X syndrome even if your parents do not have it.

Fragile X syndrome can be a cause of autism or related disorders, although not all children with fragile X syndrome have these conditions.

Review Date: 05/12/2010
Reviewed By: A.D.A.M. Editorial: David Zieve, MD, MPH, David Eltz. Previously reviewed by Diana Chambers, MS, EdD, Certified Genetics Counselor (ABMG), Charter Member of the ABGC, University of Tennessee, Memphis. Review provided by VeriMed HealthcareNetwork (8/11/2009).

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