According to this AAAS article, clinical trials are currently underway to see if blocking overactive glutamate receptors in the brain can block the effects of Fragile X, primarily mental retardation.

The hope is that once the Fragile X is suppressed, therapy can rewire the brain to allow it to overcome the limitations imposed by the haywire genetics, thus allowing people once afflicted to lead normal, healthy lives.

Fragile X

In a nutshell, Fragile X is caused by DNA methylation of the FMR1 genome on the X sex chromosome. It causes a longer face, large or protruding ears, flat feet, low muscle tone, and mental retardation. People with Fragile X have a learning rate 2.2 times less than ordinary people, and as they grow older, they lose their ability to make decisions and recall events. Verbal working memory (speech, basically) is found to decay with age; cluttered speech and self talk are common.