Fragile X Syndrome Corrected in Mice

Mar. 23 -- WEDNESDAY, Dec. 19 (HealthDay News) -- By targeting one gene, scientists have been able to correct many of the abnormalities associated with fragile X syndrome, the most common inherited form of childhood retardation.

Fragile X syndrome is caused by loss of the gene for "fragile X mental retardation protein" (FMRP). It affects about 100,000 people in the United States and is also a leading known genetic cause of autism.

There is currently no treatment or therapy for fragile X syndrome. Symptoms include mental retardation, epilepsy, and abnormal body growth.

"Fragile X is caused by the silencing of a single gene encoding FMRP," said lead researcher Mark F. Bear, director of the Picower Institute and the Picower professor of neuroscience at MIT in Cambridge, Mass. "FMRP regulates protein synthesis in the brain," he explained.

But the findings suggest that a drug could correct many of the symptoms of the disease.

"You are not doomed with the absence of this gene," Bear said. "If we could even come in late and correct it, there is a good chance that we could alter brain development and improve the symptoms," Bear said.

The report is published in the Dec. 20 issue of Neuron.

In the study, Bear's team used mice engineered to lack the FMRP gene. This caused the animals to develop many of the characteristics of human fragile X syndrome.

The lack of FMRP acts as a brake on protein synthesis in specific areas of brain circuitry. According to Bear's group, loss of this genetic "brake" allows another protein driving the syndrome -- called metabotropic glutamate receptor 5 (mGluR5) -- to get out of control.

So, a lack of functioning FMRP brings about runaway protein synthesis, Bear noted. But, "if we could dial back activity at the mGluR5 receptor, we might be able to bring the system back into balance and correct fragile X syndrome," he theorized.

Investigating that notion, Bear's team created mutant mice that lacked both the FMRP gene and had a 50 percent reduction in their production of mGluR5. They reduced rather than eliminated the activity of mGluR5, so that they could mimic what might happen if a drug treatment for fragile X was used in humans.