PNPT1 and mitochondrial DNA depletion syndrome, encephalomyopathic form with methylmalonic aciduria: Recessive mutations in the PNPT1 gene, encoding PNPase, were recently linked to human mitochondrial disease in two siblings affected by encephalomyopathy, choreoathetosis, and combined OXPHOS deficiency, and in three siblings from a second family affected by non-syndromic hearing loss (Vedrenne et al., 2012; von Ameln et al., 2012).