By altering a single gene in an animal model, researchers have demonstrated that the effects of the fragile X mutation can be reversed. As such, this research offers potential treatment of fragile x syndrome, the most common form of inherited mental retardation and a leading identified genetic cause of autism.

Fragile X syndrome is known to be caused by loss of the gene for "fragile X mental retardation protein" (FMRP), which is believed to act as a brake on protein synthesis in specific areas of brain circuitry. The authors' idea was that loss of the "brake" would allow another protein that stimulates this process, called metabotropic glutamate receptor 5 (mGluR5), to function unchecked.

Their tests on the double mutant mice revealed that the mGluR5 gene reduction greatly alleviated many abnormalities produced by loss of FMRP. The double mutant mice showed a rescue of abnormalities in brain structure and function, brain protein synthesis, memory, and body growth.

Apparently, theloss of the FMRP gene produces overgrowth of the connections among neurons called dendritic spines, but a 50% reduction in the mGluR5 gene produced mice with completely normal spine density. The double mutants also showed substantial reduction in epileptic seizures caused by lack of FMRP.

These findings were published in the December 20, 2007 issue of the journal Neuron.


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