The MT-ND5 gene spans 1.8 kb within the mitochondrial DNA between bases 12,336 and 14,147. Mutations in the MT-ND5 gene have been found in small percentage of all cases of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). The G13513A mutation was identified in at least five patients with characteristic features of MELAS. This mutation results in reduction of complex I activity, which disrupts energy production within mitochondria. Also mutations within MT-ND5 gene have been identified in about 10 patients with Leigh syndrome.