Hope for Fragile X syndrome

It is a glimmer of hope in the fragile X syndrome, the most common cause of inherited mental retardation. Some of these patients could benefit from medication to improve their behavioral problems, according to a study published today in the journal Science Translational Medicine. Especially, the response to this new molecule, which acts specifically on a receptor in the brain, would be predictable depending on genetic characteristics.

Studies are underway to consolidate on a broader scale these findings in thirty patients. But for researchers is an important first step that has been crossed in a disease previously considered incurable.

The fragile X syndrome reaches many children worldwide. It is characterized mainly by mental retardation, which may be associated with behavioral disorders: attention deficit, movements and repeated phrases, autistic behaviors, aggression etc. Patients are affected by an inability to process sensory information and the severity of symptoms of mental retardation is very variable from one individual to another. The fragile X syndrome is also under-diagnosed.

Since the discovery of the gene in question, there are two decades, researchers have made significant progress on understanding this complex disease. Everything comes from the mutation of the gene FMR 1 (fragility mental retardation 1) gene on chromosome X. This mutation, which consists of an abnormal repeat of a sequence of DNA, causes a defect of the corresponding protein FMRP. Now, it's primary role is to decrease the activity of mGlu5 receptors are essential for proper brain function and neural connections. In the end, it is the overactivation of the brain induced by mGlu5 gene mutation FMR would explain the symptoms.

Researchers tested a molecule (AFQ056) antagonist of these receptors, that is to say which reduced their activity in thirty adult patients. Half received the molecule and the other a placebo, then the two groups were switched after three weeks. By studying the scales of behavior problems, researchers have noticed a score improvement in some patients treated with AFQ056.

By comparing nonresponders to responders, they were found a specific genetic fingerprint, corresponding to a completely inactive mutated gene. 24 of the 30 participants showed few serious side effects, most commonly fatigue or headaches.

A larger trial (including 160 adult patients treated for three months) has just begun. Another will start in 2011 in adolescents, said the Novartis laboratory that develops the molecule. Several other products which are also mGlu5 antagonists, are being studied.

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