FXN and Friedreich ataxia: Defects in genes related to iron homeostasis and antioxidant systems are frequently associated with mitochondrial dysfunction, but inconsistently included under the umbrella of ‘mitochondrial disease.’ For example, Friedreich’s ataxia (FA), caused by defects in the mitochondrial iron homeostasis factor frataxin, and Sedaghatian-type spinal metaphyseal dysplasia (SSMP), caused by defects in glutathione peroxidase 4 (GPX4), are not universally included in ‘mitochondrial disease’ gene lists, though mitochondrial function is impacted by defects in these genes [4–6].