TYMP and mitochondrial disease: In addition, cerebral white matter lesions in mitochondrial syndrome are caused by a set of nuclear genes involved in maintaining the integrity of mtDNA, such as DNA polymerase gamma, and thymidine phosphorylase and MPV17 defects have also been reported.[3,9–12] Mutations in mitochondrial aspartyl-tRNA synthetase have been found to be associated with white matter lesions in the brainstem and spinal cord.[13,14] The characteristics of cerebral white matter lesions may depend on the molecular pathology of mitochondrial disease.