POLG2 encodes the minor subunit of the mtDNA polymerase, which is responsible for DNA replication of 13 proteins, 22 tRNAs, and two ribosomal RNAs (rRNAs) that are required for transcription of mitochondria‐specific proteins, including those involved in oxidative phosphorylation.39 Furthermore, patients with mutations of POLG2, who have progressive external ophthalmoplegia (PEO), have reduced mtDNA content in their cells.40 We therefore hypothesized that the Polg2‐Y265X mutation may affect the mtDNA content in Polg2+/Y265X kidneys and compared this with the Polg2+/+ kidneys (Fig. 3A). The gene discussed is POLG2; the disease is progressive external ophthalmoplegia.