Biotech Values

[Biowatch]

Statin side effects:

AMERICA’S MOST POPULAR DRUG HAS A PUZZLING SIDE EFFECT. WE FINALLY KNOW WHY.

https://www.theatlantic.com/health/archive/2023/06/the-gene-that-explains-statins-most-puzzling-side-effect/674542/

But why should an anticholesterol drug weaken muscles in the arms and legs? Recently, two groups of scientists stumbled upon an answer. They didn’t set out to study statins. They weren’t studying cholesterol at all. They were hunting for genes behind a rare disease called limb girdle muscle dystrophy, in which muscles of the upper arms and legs—sound familiar?—become weak and waste away. After both teams tracked the disease through a handful of families in the U.S. and a Bedouin family in Israel, their suspicions separately landed on mutations in a gene encoding a particularly intriguing enzyme.

The enzyme is known as HMG-CoA reductase, and to doctors, it is not obscure. It is, in fact, the very enzyme that statins block in the process of halting cholesterol production. And so, the answers to two mysteries suddenly became clear at once: Dysfunction in this enzyme causes muscle weakness from both limb girdle muscular dystrophy and statins.

This connection between a rare disease and a common drug stunned the researchers. “It seemed too good to be true,” says Joel Morales-Rosado, a pathologist who worked on one of the studies as a postdoctoral researcher at the Mayo Clinic. “One of the first things you learn in medical school is association between statins and myopathy.” Now the answer as to why— along with a potential treatment for it—has emerged from the DNA of just a few patients living with a seemingly unrelated genetic disease.

This pair of studies in the U.S. and Israel “really strongly suggests” that statins cause muscle damage via the same HMG-CoA reductase pathway, says Andrew Mammen, a neurologist at the National Institutes of Health who was not involved in either study. The enzyme’s role had been suspected, he told me, but “it had never been proven, especially in humans.” (Questions still remain, however. The enzyme, for example, is found in tissues throughout the body, so why do these common side effects show up in muscles specifically?) Rosenson, at Mount Sinai, wondered if variations in this gene could explain why statins don’t affect everyone the same. Perhaps patients who suffer particularly severe muscle side effects already have less functional versions of the enzyme, which becomes problematic only when they start taking statins, which reduce its function even further. This research might end up concretely improving the life of at least some of the patients most severely affected by statins.

That’s because Birk’s team in Israel did not stop at simply identifying the mutation. For two decades, he and his colleagues have been studying genetic disorders in this Bedouin community in the Negev and developing genetic tests so parents can avoid passing them on to their children. (Cousin marriages are traditional there, and when two parents are related, they are more likely to carry and pass on the same mutation to a child.) With limb girdle muscular dystrophy, his team went one step further than usual: They found a drug to treat it.

This drug, called mevalonolactone, allows muscle cells to function more normally even without the HMG-CoA reductase enzyme. Birk’s team first tested it in mice given doses of statins high enough to weaken their limbs; those also given mevalonolactone continued to crawl and even hang upside down on a wire just fine. They seemed to suffer no ill effects. When that experimental drug was given to the Bedouin woman bedridden with limb girdle muscular dystrophy, she also started regaining control of her arms and legs. She could eventually lift her arm, sit up by herself, raise her knees, and even feed her grandchild on her own. It was a dramatic improvement. Birk told me he has since heard about dozens of patients with limb girdle muscular dystrophy around the world who may benefit from this experimental drug.