ETHE1 and ethylmalonic encephalopathy: Ethylmalonic encephalopathy is a severe, fatal disorder caused by mutations in the ETHE1 gene which encodes a mitochondrial sulfur dioxygenase necessary for the detoxification of sulfide [196]; therefore, mutations in ETHE1 gene lead to the accumulation of hydrogen sulfide, that is a potent inhibitor of cytochrome c oxidase [197].