Metabolic Myopathies Discovered During Investigations of Statin Myopathy

Abstract

The statins have emerged as the dominant class of drug for the treatment of hypercholesterolemia. These medications are generally well tolerated. However, myalgias, the most frequent side-effect, occur in up to 7% of patients. Transaminitis and skeletal myotoxicity, with elevated serum creatine kinase (CK) levels (i.e., >10 times the upper limit of normal), occur with reported frequencies of 1% and 0.1%, respectively. Various hypotheses have been proposed to explain the relationship between statin therapy and the spectrum of muscle dysfunction manifested by myalgia, myopathy, and rhabdomyolysis.Statin-mediatd inhibition of mevalonate metabolism impairs the synthesis of isoprenylated products–the most notable of which is ubiquinone. However, isoprenylation is responsible for the post-translational modification of up to 2% of cellular proteins. Therefore, numerous metabolic pathways are potentially modified by statin-mediated hypoprenylation. Subclinical defects in one or more energy-deriving pathways may be unmasked upon exposure to the pleotropic effects of statins. Such pharmacogenomic synergism may underlie the development of “statin myopathy” in a subset of patients. In this regard, we describe four patients with mutations in the myophosphorylase (PYGM; MIM 232600), myoadenylate deaminase (AMPD1; MIM 102770), and carnitine palmitoyltransferase (CPT2; MIM 600650) genes whose diagnoses became apparent during the course of investigations for statin-induced myalgias and hyperCKemia.