ETHE1 and ethylmalonic encephalopathy: Deficiency in CSE promotes neurodegeneration in Huntington’s disease [18], whereas deficiency in ethylmalonic encephalopathy 1 (ETHE1 or persulfide dioxygenase, PDO), a H2S catabolizing enzyme, is a cause of ethylmalonic encephalopathy, which is characterized by abnormally high H2S levels in tissues and blood [19].