Interestingly, the fibroblasts from the patient (case 3) with a NAXD mutation predicted to only prevent mitochondrial NADHX repair activity (and not cytosolic repair activity) did not show decreased serine synthesis pathway activity based on these measurements, further supporting that, in this form of the disease, the predominant myopathy symptoms are caused by perturbed mitochondrial metabolism. The gene discussed is NAXD; the disease is myopathy.