Scientists reported Thursday they had identified the genetic defect that is responsible for an unusual form of inherited paralysis.

Researchers at the Massachusetts General Hospital and Harvard Medical School in Boston and the University of Pittsburgh said they had tracked down the faulty gene that causes hyperkalemic periodic paralysis.The disorder is one of a strange group of inherited illnesses that cause episodes of paralysis that are temporary but debilitating.

The defect apparently causes a malfunction in a critical pathway called a "sodium channel" located inside muscle cells. The malfuction causes potassium to build up outside the cell wall, upsetting the cell's usual balance and paralyzing the muscle.

The researchers identified the apparent genetic defect for hyperkalemic periodic paralysis by analyzing genetic material from members of families in which the disease appeared to be passed down through generations. The defect was traced to a gene located on the so-called chromosome 17.

"We still have only a statistical correlation rather than proof that our candidate gene causes hyperkalemic periodic paralysis," said Dr. Robert Brown Jr., an assistant professor of neurology at Harvard Medical School, who helped conduct the research.