Fragile X syndrome (FXS) is a genetic condition that causes intellectual disability, behavioral and learning challenges, various physical characteristics and, in some cases, seizures. Though FXS occurs in both genders, males are more frequently affected than females, and generally with greater severity. 1   It is also the leading known genetic cause of autism.

Prevalence

Fragile X Syndrome (FXS) is the most common cause of inherited intellectual disability and most common known genetic cause of autism, which affects 1 in 88 children in the United States. Approximately one-third of all children with FXS have autistic-like symptoms. Of children diagnosed with an autism spectrum disorder, roughly 5% have FXS as well. The full mutation appears in approximately 1 in 3,600 to 4,000 males and 1 in 4,000 to 6,000 females. The premutation occurs in about 1 in 260 females and 1 in 800 males, although recent studies indicate the prevalence of female carriers may be as high as 1 in 130. Those who carry the permutation, also referred to as “carriers”, have a high chance of passing either the full mutation or the premutation to their offspring.  Approximately 1,000,000 Americans have or are at risk of developing FXS or a related disorder. 2

Characteristics

The majority of males with fragile X syndrome have a significant intellectual disability. The spectrum ranges from subtle learning disabilities to severe intellectual disability and autism. Behavioral characteristics include attention deficit disorders, speech disturbances, hand biting, hand flapping, autistic behaviors, poor eye contact, and aversion to touch and noise. While some females with fragile X syndrome will exhibit these characteristics, fewer females are affected and their degree of impact is usually diminished.

Because fragile X presents itself in such a myriad of ways, it is often challenging for families to get a clear diagnosis of the disorder. In fact, it is thought that a high percentage of those affected with FXS are undiagnosed or misdiagnosed.

Cause

The condition is caused by abnormalities in a specific gene on the X chromosome, a strand of DNA that carries hereditary information.

Children with fragile X syndrome don’t produce enough of a certain protein known as the fragile X mental retardation 1 (FMR1) protein, causing cognitive and behavioral impairments. Females are less affected than males because females have two X chromosomes (while males have one X and one Y). Males with fragile X only have the nonfunctioning gene while females with fragile X have one normally functioning gene which partially compensates for the nonfunctioning gene.

Men with the premutation will pass the altered gene to all of their daughters and none of their sons. Women with the premutation have a 50% chance of passing the altered gene to all of their offspring.

Treatment

Special education, speech and language therapy, occupational therapy and behavioral therapies help to address many of the physical, behavioral, and cognitive impacts of Fragile X Syndrome. Medical intervention can help with aggression, anxiety, hyperactivity and poor attention span.   These interventions treat the symptoms as currently, there is no fully effective treatment for Fragile X Syndrome.  However, clinical trials are proving to be successful and a Fragile X Syndrome “cure” is on the horizon.

For more detailed information on Fragile X Syndrome and related disorders, go to www.fragilex.org  or search “Fragile X Syndrome” at www.nih.gov

1, 2  – Source: www.fragilex.org

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