Boston Heart Diagnostics this week launched its Statin Induced Myopathy Genotype test, which the company will market to doctors as a way to identify patients at heightened risk of severe muscle pain following treatment with certain statins.
The Statin Induced Myopathy Genotype test gauges variants in the SLCO1B1 gene, which is associated with a heightened risk of developing severe myopathy after taking statins. The SLCO1B1 rs4149056 genotype that the test analyzes has been shown in studies to "significantly decrease" people's ability to metabolize statins, as well as to confer a heightened risk of myopathy.
Approximately 40 million people in the US take statins each year to lower low-density lipoprotein cholesterol and reduce the risk of heart attack and stroke. According to the company, statin users who are heterozygous for the SLCO1B1 risk allele are about five times more likely to suffer myopathy as a side effect of statins, while those who are homozygous for the risk allele are about 18 times more likely to experience a side effect.
Furthermore, the risk for myopathy "is especially pronounced in those receiving high doses of the lipophilic statins simvastatin and atorvastatin," BHD said in statement. "The physician or healthcare provider should consider using lower doses of water-soluble statins (pravastatin 20 mg/day or less, pitavastatin 2 mg/day or less, rosuvastatin 10 mg/day or less, or fluvastatin 20 mg/day or less) and adding [other cholesterol lowering medications] ezetimibe or colesevelam therapy to augment LDL-C lowering response if needed."
Drug developers are marketing generic versions of several of the above statins. Simvastatin is marketed under the brand name Zocor by Merck; atorvastatin, marketed by Pfizer as Lipitor, lost patent protection last year.
The labels of simvastatin, atorvastatin, and other treatments in the class don't mention SLCO1B1's association with drug-induced myopathy risk. A labeling update from the US Food and Drug Administration might help drive adoption of BHD's test, but such an update would require data submissions to the agency proving the clinical validity of the gene's impact on statin-related adverse reaction.
BHD President and CEO Susan Hertzberg told PGx Reporter that the company is currently figuring out its marketing strategy for the test. The firm is offering it through its Framingham-based CLIA lab as a lab-developed test.
A BHD spokesperson further reflected that while developers of generic statins could potentially be partners to conduct additional validation and cost-effectiveness studies to drive adoption of the Statin Induced Myopathy Genotype Test, generic drug developers generally do not invest heavily in R&D.
BHD has an exclusive US license for the SLCO1B1 rs4149056 marker from the University of Oxford's technology transfer company Isis Innovation. The USPTO has fast-tracked the examination of Oxford's patent covering the marker, and BHD expects a final decision before the end of this year.
Until the patent is granted, Quest subsidiary Berkeley Heart Lab is free to market its SLCO1B1 Genotyping Test, which gauges the same gene variants analyzed by BHD. "Until there is a patent, there is no infringement, so technically, [BHL] could be in that market," Hertzberg said. "But generally speaking, companies generally withdraw tests because you don't want to be promoting a test that you know nine months from now you're going to have to [remove from] the market."
BHD has asked BHL to voluntarily withdraw the test and to collaborate on transitioning any physicians who have ordered BHL's SLCO1B1 Genotyping Test to BHD. "But, I haven't heard back from them yet," Hertzberg said.
In the patent application – which describes a diagnostic method of assessing risk of statin-induced myopathy by detecting the presence of SLCO1B1 rs4149056 polymorphisms – the inventors note that among those taking standard doses of simvastatin (20-40 mg daily) the incidence of myopathy is around one per 10,000 patients annually. As such, "the impact of these gene variants on the absolute risk of myopathy is likely to be small," the inventors said. However, they point out that the risk of this adverse reaction may be heightened ten-fold with higher doses of simvastatin (80 mg daily) and other statins.
"Hence, the use of such drugs in people taking high-dose statin regimens who have the C allele of the rs4149056 polymorphism may produce particularly high absolute risks of myopathy," the inventors write.
According to BHD, statin users with the SLCO1B1 rs4149056 C/T gene variant are five times more likely to experience myopathy than those with the T/T normal genotype. Meanwhile, people who carry the SLCO1B1 C/C variant have an 18 times greater risk of experiencing myopathy compared to non-carriers.
According to statistics cited by BHD, between 25 percent and 50 percent of patients prescribed statins stop taking them for a number of reasons. Although statin-induced myopathy is rare, it is a serious adverse drug reaction that could cause some patients to stop using these drugs and be at heightened risk of cardiovascular events.
A study published online last year in the Pharmacogenomics Journal by researchers at the University of British Columbia and elsewhere sought to replicate previously reported associations between the SLCO1B1 rs4149056 variant and severe myopathy, as well as to determine whether this risk varied depending on the specific statin. While the variant was not significantly associated with myopathy in the group as a whole, the researchers found that genotype was "significantly associated with myopathy in patients who received simvastatin, but not in patients who received atorvastatin."
These findings "provide further support for a role for SLCO1B1 genotype in simvastatin-associated myopathy, and suggest that this association may be stronger for simvastatin compared with atorvastatin," the study authors concluded.