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Title: Genome-wide association of statin-induced myopathy
Author: Link, Emma
ISNI:       0000 0004 2676 7541
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2009
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Lowering LDL-cholesterol with statin therapy produces substantial reductions in cardiovascular events, and larger cholesterol reductions may produce larger benefits. Rarely, myopathy occurs with statins, especially at higher doses and in combination with certain medications. Similarly strong associations might exist between myopathy with high-dose statin regimens and genetic variants, especially those affecting blood statin levels. This study aimed to find genetic variants associated with statin-induced myopathy. A feasibility study was completed to assess whether plausible effect sizes of 5 to10-fold higher risks per genetic variants could be detected among 50-100 cases with statin-induced myopathy and to consider the best study design. A genome-wide association study was then carried out using approximately 300,000 genetic markers (and additional fine-mapping) in 85 people with definite or incipient myopathy and 90 controls, who were all taking 80mg simvastatin daily in a 12,000 participant trial of 80mg vs 20mg simvastatin daily. The cases were also compared to 2,300 additional controls who had not been exposed to intensive-dose statin therapy. Replication of the myopathy result and lipid-lowering associations were tested in a 20,000 participant trial of 40mg simvastatin daily versus placebo. The genome-wide scan yielded a single strong association (p = 4x10-9) of myopathy with the rs4363657 single nucleotide polymorphism (SNP) located within the SLCO1B1 gene on chromosome 12. This non-coding SNP was in nearly complete linkage disequilibrium (r2=0.97) with the non-synonymous rs4149056 SNP. The population prevalence of the rs4149056 C allele was 15%, and the odds ratio for myopathy was 4.5 (95% confidence interval 2.6 to 7.7) for each copy of the C allele and 16.9 (4.7 to 61.1) for CC vs TT homozygotes. Over 60% of these myopathy cases could be attributed to the C variant. The SLCO1B1 gene encodes the organic anion transport polypeptide OATP1B1, which has been shown to regulate hepatic uptake of statins. In literature reports, rs4149056 reduced statin transport and was associated with 37% (31% to 44%) higher systemic statin acid levels per C allele. The association of rs4149056 with myopathy was replicated in the trial of 40mg simvastatin daily, which also showed that it was associated with the cholesterol-lowering effects of simvastatin. No SNPs in any other region were clearly associated with myopathy (although comparison of the myopathy cases with the 2,300 controls identified a region of chromosome 1p12 that warrants further study). This study identified common variants in SLCO1B1 that influence the risks of statin-induced myopathy substantially. Genotyping these variants may be useful for tailoring both the statin dose and safety monitoring. More generally, such studies of the genetic determinants of serious adverse reactions with other drug classes may help to improve the balance between treatment efficacy and safety.
Supervisor: Parish, Sarah ; Rory, Collins Sponsor: Commonwealth Scholarship Commission
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Medical Sciences ; Cardiovascular disease ; Epidemiology ; Genetics (medical sciences) ; statin ; myopathy ; rhabdomyolysis ; genome-wide association study ; candidate gene study