Genetic Cause of Statin-Related Muscle Pain Found

British researchers identify variant that increases risk of myopathy at high doses

By Ed Edelson
HealthDay Reporter

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WEDNESDAY, July 23 (HealthDay News) -- British researchers have discovered a genetic variant that causes some people who take cholesterol-lowering statins to have the muscle weakness called myopathy.

"We found a variant that affects the transport of statins into the liver," said Dr. Rory Collins, a professor of medicine and epidemiology at the University of Oxford and a leader of the group reporting the discovery in the July 24 online issue of the New England Journal of Medicine. "That variant produces a high level of blood statins and accounts for the greatest proportion of myopathy in people who use statins."

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That side effect is not common, although it has been reported in a number of studies. It occurs in fewer than one of every 1,000 people taking statins. The new study indicates that one copy of the myopathy-related variant is carried by about a quarter of the population, Collins said, with a much smaller percentage carrying two copies. The variant accounts for about 60 percent of all statin-related myopathy cases, Collins said.

"It causes a substantial increase in relative risk," he said. "The risk is increased about fourfold for those who have one variant version of the gene, about 15-fold for someone who inherits two variant versions."

All human genes come in pairs, one from each parent.

Even when the variant version is present, the risk of myopathy depends on how big a dose of a statin is prescribed, Collins said. "For the statin doses most usually used, 20 to 40 milligrams of simvastatin, for example, the risk of myopathy is very low," he said. "Using a high dose for someone at high risk, the absolute risk of myopathy is maybe one in 1,000. With a standard dose, the risk would be about one in 10,000."

The myopathy caused by statins generally is not severe, and it disappears a day after the medication is stopped.

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