Given the identification of mutations in genes encoding proteins involved in mt-tRNA modification as a cause of mitochondrial disease (e.g., PUS1 [Bykhovskaya et al., 2004], TRMU [Zeharia et al., 2009], MTO1 [Ghezzi et al., 2012], MTFMT [Tucker et al., 2011], the disruption of these post-transcriptional modifications represents a major consideration for potential disease mechanisms. Here, PUS1 is linked to mitochondrial disease.