ETHE1, also known as HSCO, is a sulfur dioxygenase that localizes within the mitochondrial matrix. ETHE1 probably plays an important role in metabolic homeostasis in mitochondria. It may also function as a nuclear-cytoplasmic shuttling protein that binds transcription factor RELA/NFKB3 in the nucleus and exports it to the cytoplasm. ETHE1 can suppresses p53-induced apoptosis by preventing nuclear localization of RELA. Mutations in ETHE1 gene result in ethylmalonic encephalopathy. Ethylmalonic encephalopathy is an autosomal recessive, invariably fatal disorder characterized by early-onset encephalopathy, microangiopathy, chronic diarrhea, defective cytochrome c oxidase (COX) in muscle and brain, high concentrations of C4 and C5 acylcarnitines in blood and high excretion of ethylmalonic acid in urine.