Ex vivo culturing of primary CD138 + MM cells derived from the BM of prospective patients with MM with and without elevated serum LDH levels was performed in cell culture media containing 1mM (approximate physiologic concentrations in the human body) of 100% enriched 3- 13C-Lactate and 100% enriched U-13C-Glucose as previously described. This evidence concerns the gene SDC1 and Miyoshi myopathy.