Disruption of Fe-S assembly in ISCU myopathy causes depletion of FECH. (A) As reported previously, total ISCU protein levels were depleted in vastus lateralis muscle biopsies taken from Swedish patients with ISCU myopathy (lanes designated as P1-P3), compared with 3 healthy controls (designated C1-C3), and a patient with an unrelated mitochondrial myopathy (designated as M1). A prominent protein band observed after Ponceau-S staining of the filter served as the loading control. (B) FECH protein levels were also greatly decreased in the ISCU myopathy biopsies, as were levels of the Fe-S cluster-containing enzyme mitochondrial aconitase. (C) Primary myotube cultures obtained from an ISCU myopathy patient as well as from a healthy person (control) were terminally differentiated by growth in low serum conditions (“Tissue biopsies and myoblast culture”). Although FECH and ISCU levels increased in both control and patient cultures during the course of the experiment, the relative level of both proteins was diminished in the patient cultures compared with the control at every given time point. (D) Little difference in FECH mRNA levels was seen in control and patient myotube cultures at zero and 5 days of differentiation, as assessed by Northern blot.