The R19H mutation in COXVIB1 causes mitochondrial encephalomyopathy [70], while the R20C mutation in COXVIB1 not only causes encephalomyopathy but also cardiomyopathy and hydrocephalus [71]. This evidence concerns the gene COX6B1 and mitochondrial DNA depletion syndrome, encephalomyopathic form with methylmalonic aciduria.