Fragile X is the most common inherited form of mental retardation and is estimated to affect approximately 90,000 people in the United States . The condition is caused by a mutation in the FMR1 gene on the X chromosome that prevents expression of a single protein, fragile X mental retardation protein (FMRP). Brain development in the absence of FMRP gives rise to the major symptoms of Fragile X syndrome in humans. Psychiatric and behavioral characteristics of FXS include impaired cognitive function, developmental delay, attention deficit and hyperactivity, anxiety, and obsessive-compulsive and autistic behaviors.

The specific functions of FMRP are under intensive investigation and studies indicate it has a major role in regulating the protein synthesis required for normal brain development. If we are correct that Fragile X symptoms and disabilities are due to disrupted regulation of brain protein synthesis, it is reasonable to anticipate that other developmental disorders with similar symptoms might be traced to defects in associated molecular pathways. Indeed, other types of human developmental disorder, including autism, have many of the same core psychiatric and behavioral characteristics as Fragile X Syndrome.

Unmet Therapeutic Need

No drugs have yet to be developed to specifically treat Fragile X syndrome. Although antidepressants and antipsychotics are commonly prescribed "off-label" to treat specific symptoms in patients with FXS and autism, there are no drugs approved by the FDA to enhance cognitive function of people with developmental disorders. Drugs currently used in developmental disorders primarily focus on treating specific symptoms such as anxiety or improving and controlling behavior. While some of these compounds may improve function to a limited degree, the poor efficacy of drugs used to treat FXS results in a vast unmet medical need.

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