Tweaking a gene may fix Fragile X syndrome

Dec 20 2007

According to new research clues to Fragile X syndrome may be connected to one single human gene.

Fragile X syndrome is the most common inherited cause of mental retardation and autism and affects 90,000 to 100,000 Americans.

Fragile X syndrome can cause seizures, impaired memory, learning disabilities, hyperactivity, severe mental retardation and accelerated body growth.

It is a genetic disorder caused by mutation of the FMR1 gene on the X chromosome.

Apart from intellectual disability, prominent characteristics of the syndrome include an elongated face, large or protruding ears, flat feet, larger testicles in men and low muscle tone; speech too may be affected and may include cluttered or nervous speech.

Behaviour may include stereotypic movements such as hand-flapping and poor social development, particularly shyness and limited eye contact and some individuals with the fragile X syndrome also meet the diagnostic criteria for autism.

Fragile X syndrome is more common in males often resulting in severe intellectual disability but while most females experience symptoms to a lesser degree they too can develop just as severe symptoms.

There is no current cure for the syndrome which is commonly treated with behavioral therapy, special education, medication, and when necessary, treatment of physical abnormalities.

Researchers at the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology conducted a study using mice and found that with genetic engineering they were able to alter the gene in mice which caused the worst symptoms of Fragile X syndrome.

The researchers say their findings support the theory that many of the symptoms of Fragile X stem come from too much activation of one of the brain's chief network managers, a protein called the metabotropic glutamate receptor or mGluR5.

FMRP and mGluR5 control one another and when a mutation cuts out FMRP, mGluR5 signals run rampant.

The researchers discovered that by reducing levels of mGluR5 in the brains of mice, many symptoms of Fragile X syndrome were also reduced and they suggest that some experimental drugs could have the same effect.

The researchers have also conducted experiments with a drug called MPEP which interferes with mGluR5, for a variety of conditions, including drug addiction and anxiety.

Lead author Professor Mark Bear says their findings have major therapeutic implications for Fragile X syndrome as well as autism.

Professor Bear says if the new drug is proved to be safe the first trials would be in adults with Fragile X, however maximum benefit could be expected if treatment is begun early in life.

He says the ultimate goal would be to have the drug approved for use in affected children.

Experts advise those with the fragile X syndrome in their family histories to seek genetic counseling to assess the likelihood of having children who are affected, and how severe any impairments may be in affected descendants.

The study is published in the December 20, 2007, issue of the journal Neuron.