Hypersensitivity to BSO has been described in fibroblasts from patients with Leigh’s syndrome caused by a mutation in SURF1 (a gene encoding a mitochondrial chaperone involved in cytochrome oxidase assembly) [24] or two mutations in the ND3 and NDUFA1 subunits of complex I [23], as well as in fibroblasts of patients with MELAS (myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) caused by mutations in two mitochondrial tRNAs [23]. The gene discussed is SURF1; the disease is MELAS.