GLRX5 and myopathy: Tissue-specific defects in mitochondrial ISC synthesis have more recently been identified in patients with isolated myopathy (Mochel et al., 2008; Olsson et al., 2008) or sideroblastic anemia (Camaschella et al., 2007), which are linked to mutations in the scaffold ISCU and the enzyme glutaredoxin 5, respectively.