POLG and mitochondrial encephalomyopathy: As an example, CIPO is a feature associated with mitochondrial encephalomyopathies that can be caused by mutations in TYMP, a gene coding for thymidine phosphorylase, but also by polymerase gamma (POLG) mutations, or mutations in the mitochondrial DNA (mtDNA), which occur in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) [13].