Epilepsy gene identified.

A joint U.S.-Finnish team reports nabbing a gene that, when mutated, causes an inherited form of epilepsy.

Richard M. Myers and Len A. Pennacchio of the Stanford University School of Medicine and their colleagues in Finland knew from previous work that the gene for progressive myoclonus epilepsy resides on chromosome 21. They used landmarks along the DNA to zero in on a specific region of the chromosome.

Their research, which appears in the March 22 Science, identifies the culprit as a gene carrying the blueprint for a protein called cystatin B.

Progressive myoclonus epilepsy occurs when a person inherits two defective copies of this gene. A serious disorder that's relatively common in Finland but rare in the United States, the disease results in seizures and mental deterioration that eventually leads to senility.

Researchers don't know why a defect in the gene triggers the disorder.

However, the team's results suggest that the mutant form of the gene leads to reduced production of cystatin B. Cystatin B is a member of a class of proteins called protease inhibitors.

This study marks the first time that a protease inhibitor has been linked to epilepsy, Pennacchio says. Moreover, scientists don't understand why a protease inhibitor would play a role in epilepsy. The finding will most likely spark investigations into whether other forms of the disease are linked to defects in genes coding for these proteins.

The discovery may also lead to a method of identifying carriers of the defect, Pennacchio says. People with a family history of the disorder may want genetic testing before having children, he adds.