A 48-year man came to his cardiologist for an unscheduled visit complaining of worsening muscle pain and weakness in his arms and legs. He was finding it hard to exercise and even climb stairs.
Two weeks before, the man had been fitted with a stent in his right coronary artery after he showed signs of coronary artery disease and put on antiplatelet drugs and atorvastatin, one of a type of cholesterol drugs called statins. He was also taking metoprolol and ramipril, as well as the antiplatelet agents aspirin and clopidogrel.
The man’s cardiopulmonary and neurological examinations came back normal. He was also screened for a number of conditions that ended up not being the culprit, including chronic diabetes, decreased thyroid activity and kidney dysfunction. Laboratory measurements revealed only mildly elevated levels of creatine kinase (CK), an enzyme created when muscle tissue is damaged.
The man was taken off atorvastatin, and the symptoms progressively decreased after only a few days.
What makes this case interesting is not solely the 48-year-old’s experience, but that of his 65-year-old father.
The 65-year-old was also experiencing limb muscle weakness and was taking the same dose of atorvastatin as his son. The father also had slightly increased CK levels during atorvastatin therapy. Once he was taken off the medication, his muscle weakness disappeared and his CK levels returned to normal.
Doctors suspected a genetic basis for the muscle weakness given the father-son relationship and the near-identical symptoms after starting atorvastatin. Genotyping revealed both men to be carriers of a variation in the gene SLCO1B1 that resulted in reduced activity in the SLCO1B1-coded drug transporter.
Research has shown that variations resulting in decreased SLCO1B1 transporter activity may lead to increased statin blood levels and increase the risk of adverse effects, such muscle weakness (also known as myopathy). Pharmacogenetic testing, such as that offered by Genelex, can help identify these variations.
Although SLCO1B1 genotyping of all patients before initiating statin therapy is not recommended, the case study authors write, physicians should bear in mind that such testing may be useful for patients with a family history of statin-associated myopathy or other side effects. Test results could inform doctors on choice of statin and dose and if close monitoring after administering statins is called for.