Fragile X syndrome (patient information)

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Fragile X syndrome (patient information)
Location of FMR1 gene
ICD-10 Q99.2
ICD-9 759.83
OMIM 309550
DiseasesDB 4973

Fragile X syndrome


What are the symptoms?

What are the causes?

Who is at highest risk?


When to seek urgent medical care?

Treatment options

Where to find medical care for Fragile X syndrome?


What to expect (Outlook/Prognosis)?

Possible complications

Fragile X syndrome On the Web

Ongoing Trials at Clinical

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor-in-Chief: Alexandra M. Palmer


Fragile X syndrome, also called Martin-Bell syndrome or Marker X syndrome, is a genetic condition involving changes in part of the X chromosome. It is the leading inherited cause of intellectual disorder and autism spectrum disorder with severe behavioral abnormalities . It is an X linked disorder, affecting both males and females. It is a genetic disease caused by CGG trinucleotide expansion (>200 CGG repeats).

What are the symptoms of Fragile X syndrome?

The physical features of Fragile X syndrome is prominent around the time of puberty. Physical features include:

  • Large and protruding ears
  • Elongated face
  • Macroorchidism (large testicles in men after puberty)
  • Flat foot
  • High Arched palate
  • Hyperflexible finger joints
  • Low muscle tone

The common features in child with Fragile X Syndrome include low IQ with learning difficulties (intellectual disabilities). Behavioral abnormalities includes stereotypic movements (e.g., hand-flapping) hyperactivity, inattention, poor social interaction, limited eye contact and poor memory. Child with Fragile X syndrome often presents with developmental delay (including delayed attainment of motor and language milestones). Approximately, 20% of boy with Fragile X syndrome develops seizures (mostly simple or complex partial seizures)

What are the causes of Fragile X syndrome?

Fragile x Syndrome is a genetic disease which is caused by mutation in the Fragile x Mental Retardation 1(FMR1) gene in X chromosome. Generally, these mutation (>200 repeats of CGG) occurs at in the 5' untranslated region of FMR1.[3] In around 2% of cases, Fragile X syndrome can occur as a result of point mutation in FMR1 gene.[4]

Normally, the FMR1 gene makes a protein you need for your brain to grow properly. A defect in this 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 is likely to affect them more severely. You can have Fragile X syndrome even if your parents do not have it.

Who is at highest risk?

There are no established risk factors for Fragile X syndrome. However, the child with family history of Fragile x Syndrome, autism disorder of unknown cause, developmental delay, adult onset ataxia/tremor or any intellectual disabilities are at greater risk of developing the disorder.

How to know you have Fragile X syndrome?

The diagnosis of Fragile X Syndrome is based upon detection of an alteration in the fragile X mental retardation 1 (FMR1) gene. Clinically, mentally retarded child with family history of Fragile X syndrome (especially a male relative) have higher chance of inheriting the disease. There are very few outward signs of Fragile X syndrome in babies. Babies may have a large head circumference. Measurement of oversized testes in males who have reached puberty may also suggest the diagnosis. An experienced geneticist may note subtle differences in facial characteristics. Mental retardation is the hallmark of this condition and, in females, this may be the only sign of the disease. A specific genetic test called polymerase chain reaction (PCR) is used to diagnose this disease. This test looks for an expanded mutation (called a triplet repeat) in the FMR1 gene.

When to seek urgent medical care

Call your health care provider if you suspect the possibility of Fragile X syndrome in a child with mental retardation.

Treatment options

There is no specific treatment for Fragile X syndrome. There are some medication under trial such as fenobam (mGLUR5 antagonist) and Lithium (mGLUR5 signaling inhibitor). Effort is directed toward training and education so that affected children can function at as high a level as is possible. Because the condition is not rare, specific educational approaches have been developed and tested.

Diseases with similar symptoms

Fragile X syndrome must be differentiated from Autism Spectrum Disorder, Attention deficit hyperactivity disorder (ADHD), Fragile XE syndrome (FRAXE), Klinefelter syndrome and Prader-Willi syndrome (PWS).

Where to find medical care for Fragile X syndrome

Directions to Hospitals Treating Fragile X syndrome

Prevention of Fragile X syndrome

Genetic counseling and prenatal screening is recommended when one of the parents is shown to be a carrier of fragile X. Prenatal testing can be done by amniocentesis at 16-20 weeks or by chorionic villus sampling (CVS) at 10-13 weeks to determine if a fetus has inherited the fragile X gene

What to expect (Outlook/Prognosis)

The outcome depends on the extent of mental retardation. Life expectancy is normal.

What are the possible complications?

Complications in Fragile X syndrome patient may include scoliosis or mitral valve prolapse (most frequently encountered cardiac defect).


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