Mixed medication In a very small number of patients taking statins, a condition called myopathy can develop, causing severe muscle pain and weakness.
Until now, scientists have been unable to explain why the condition occurs in some patients and not others. It is hoped that the discovery will pave the way for a simple genetic test to identify patients at risk of developing myopathy, making it easier to tailor treatment to individual patients. The findings are published in the New England Journal of Medicine.
Statins are taken by about 3.4 million people in England and are one of the safest medicines available. They are taken to lower dangerous levels of LDL (low density lipoprotein) or ‘bad’ cholesterol in the blood that has been linked to cardiovascular disease and stroke. It is estimated that statins save nearly 10,000 lives in England every year.
However about one in 10,000 people on a standard dose of statins develops myopathy - for those on a high dose the risk rises to one in 1,000.
Most people are prescribed a standard dose of statins (e.g 20-40mg simvastatin daily) which is linked to very few cases of myopathy. However people on higher doses are more at risk – especially if they have the gene variation.
The Oxford team discovered that a genetic variation of a gene called SLC01B1 was responsible for 60 per cent of the myopathy cases in people taking high dose statin therapy (80mg simvastatin daily).
The SLC01B1 gene is responsible for controlling the amount of statins that get taken up by the liver and the genetic variation appears to impair its function, allowing more statin to enter the bloodstream.
‘We believe that this is the first time anyone has scanned the complete human genome for the genetic culprit of a drug’s side effect, and we’re very excited about the results,’ said team leader Professor Rory Collins.
‘A DNA test based on these findings could guide doctors as to whether a patient at high risk of heart disease will cope with a high dose of a statin, which might be more effective than a standard dose at preventing a heart attack or stroke. If the patient doesn’t have the gene variation, they’re likely to be at low risk of myopathy even on high statin dose.’
Collins points out that the technology for a simple test for the gene variation is already available and would be very inexpensive to implement. He added that the increased risk from the gene variant in people on standard doses is so small that the test would not be suitable for routine use in all people taking statins.
'Fortunately, statin-induced myopathy is very rare and reversible if the symptoms are recognised and the drug is stopped, so it would not be necessary to screen all people prescribed usual doses,' said Professor Peter Weissberg, Medical Director at the British Heart Foundation.
‘However, for those who require a higher dose or who are taking medicines that could interact with the statin, a genetic test could be used to guide prescribing to avoid myopathy. This approach will help us to optimise treatments to prevent heart attacks and strokes in individuals at high risk.’
Weissberg suggests that those people who were on high doses of statins who were discovered to carry the gene variant could be monitored more closely for signs of myopathy and if symptoms developed then treatment could be adjusted.
‘The genetic variation increases the level of statins in the blood and so those who carry it may reap the same health benefits from lower doses,’ points out Weissberg, ‘There are also alternative treatments such as the cholesterol absorption inhibitor ezetemide that could be used along side low doses of statins.
‘For now, if people are troubled by side effects from their medicines they should discuss them with their doctor.’