Mitochondrial mosaic staining for cytochrome c oxidase in liver has previously been reported in six subjects: (i) one with Alpers syndrome caused by pathogenic mutations in POLG, (ii) one with Pearson disease, (iii) in another subject with POLG deficiency [14], (iv) in an infant with encephalopathy and cholestatic giant cell hepatitis, (v) in a subject with fatal infantile hepatic failure due to mutations in POLG [26, 35], and (vi) in a subject with MEGDEL syndrome [36]. The gene discussed is POLG; the disease is liver failure.