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Research scientists discover gene defect responsible for epilepsy

University Of Bonn (Universit : 21 March, 2007  (Technical Article)
Some 70 million people world-wide suffer from what is known as idiopathic epilepsy. The symptoms can vary considerably, ranging from brief unconsciousness and twitching of arms or legs to serious attacks of cramp. Research scientists at the Universities of Bonn, Ulm and Aachen have now been able to identify a gene that, if not properly functioning, can trigger all forms of commonly occurring idiopathic epilepsy. Their findings have just been published in the renowned science journal 'Nature Genetics'.
Some of the cautionary tales of 'Struwwelpeter' read like the observations of an epilepsy researcher. Take the character Johnny-Look-in-the-Air: 'it was always Johnny's rule, to be looking at the sky' until 'Bump! Dump!', down he fell. He might well have suffered from an absence epilepsy. 'This variant usually affects children of 4 and 5 years of age,' explains the Bonn medical scientists Dr. Armin Heils. 'They lose consciousness for ten or twenty seconds and turn their eyes skywards, but carry on walking until they finally trip and fall.' In other cases, when children reach the age of 10 or 12 they suddenly turn into 'Fidgety Philip': after waking up, or when sitting at the breakfast table, their arms and legs begin to twitch involuntarily, they sweep plates from the table, or drop their cups of cocoa.

'We make an overall distinction between seven different types of so-called idiopathic epilepsies,' explains Dr. Heils. The most dangerous are referred to as 'grand mal' seizures, which are associated with loss of consciousness, severe muscle cramps and foaming at the mouth. 'What all these forms have in common is that they tend to run in the family. The predisposition is inherited, and some rare types are actually caused by a single gene defect.' The Bonn epileptologists have become the first scientists world-wide to identify a gene which, if defective, can cause various types of idiopathic epilepsy. Which form is ultimately manifested in the patient probably depends on other genes.

Every nerve cell communicates with numerous neighbouring cells via electrical impulses. An epileptic attack occurs when these impulses proliferate. A single initial signal can then lead to an electrical response on millions of nerve cells. This is normally prevented by a tiny messenger substance known as 'GABA'; which makes the nerve cells less excitable. The sedative Valium is in a sense modelled on a GABA.

Whether GABA is really able to constrain the process of signal proliferation depends, however, on the concentration of chloride in the nerve cells. If it is too high, the messenger substance acts more like an accelerator. The epilepsy gene contains a blueprint for a channel through which chloride ions from the nerve cells can escape. If an error has been written into the blueprint, the channel becomes useless and the chloride concentration rises in the cells, so that GABA can no longer developed the desired action. Epileptic attacks are the consequence.

The Bonn team studied a total of 46 families in which at least two members have suffered from an idiopathic epilepsy. 'In three families, the gene for the chloride channel had mutated; all the epileptic family members had inherited the defective gene, while the healthy members hadn't,' reports Dr. Heils. In one of these families the channel remained partially functional despite the mutation; these patients have suffered only rare attacks of epilepsy, which were milder than those found in the other two families. 'The patients have suffered from completely different forms of idiopathic epilepsy,' Dr. Heils added, explaining that this was 'an indication that other genes play a role in the disorder.' In contrast, the researchers looked at a control group of 360 healthy persons and found no changes in the channel gene.
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