Of note, upregulation of P5CR and PYCR1 has been previously reported in another mouse model of mitochondrial myopathy (muscle‐specific COX15 KO mouse; Dogan et al, 2018), and we also detect upregulated PYCR1 in MERRF muscle, suggesting that proline synthesis is a common metabolic adaptation in mitochondrial myopathies. This evidence concerns the gene COX15 and Mitochondrial myopathy.