H6PD and myopathy: In muscle SR, hexose-6-phosphate dehydrogenase (H6PD) reduces NADP+ to produce the NADPH needed for steroidogenesis, and H6PD-deficient skeletal muscle exhibits a myopathy characterized by abnormal SR structure (Lavery et al., 2006; Rogoff et al., 2010), activation of stress-induced UPR (Bujalska IJ et al., 2008), and dysregulation of Ca2+ metabolism (Ying, 2006).