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Retardation check hope

New Delhi, Dec. 19: Indian and US scientists have pushed medicine a big step closer towards correcting the most common form of inherited mental retardation and a leading cause of autism.

In studies on mice, researchers at the Massachusetts Institute of Technology (MIT) and two national laboratories in Bangalore have corrected symptoms caused by the genetic disorder called Fragile X Syndrome (FXS).

Their findings, to appear tomorrow in the journal Neuron, are based on the genetic correction of FXS in mice. But the research leap has bolstered hopes that drugs may also be able to achieve the same effect in humans.

“The mutation that causes FXS leads to abnormalities in the structure and functions of the brain. These studies show us how they might be corrected through a very specific mechanism,” said team member Sumantra Chattarji, a neurobiologist at the National Centre for Biological Sciences in Bangalore.

“This is the first mechanism of treatment for FXS for which drugs are already in the pipeline,” Chattarji said.

The studies have cemented evidence for the idea that the FXS mutation leads to over-activation of a gateway, called mGluR5, on the surfaces of brain cells. In people — or mice — with FXS, mGluR5 runs rampant.

“Fragile X is a disorder of excess — excess protein synthesis, memory extinction, body growth and excitability — and remarkably all the excesses can be reduced by reducing mGluR5,” said Mark Bear, lead author of the study and neuroscience professor at MIT.

The studies have shown that a 50 per cent reduction in mGluR5 — achieved by a genetic route — corrected the abnormal connections between brain cells, improved brain development and memory, restored body growth and reduced seizures — symptoms experienced by FXS-affected humans.

Doctors estimate that one in 3,600 males and one in 4,000 to 6,000 females have FXS, which has no known cure. It is caused by mutation in a single gene and its symptoms can range from learning disabilities to severe mental retardation, social and emotional problems as well as growth abnormalities.

The findings have raised hopes among parents of children affected by FXS.

Chattarji and neurophysiologist B. Shankaranarayan Rao, from the National Institute of Mental Health and Neurosciences in Bangalore, found that mice with FXS mutation, along with lower levels of mGluR5, had healthy connections between brain cells.

“Their brains looked no different from those of ordinary mice. It’s encouraging,” Chattarji said. The move from the genetic route in FXS animals to drug trials in humans might be fast because drugs that lower mGluR5 had been developed decades ago by companies for other conditions.

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