The enzyme encoded by the GSR gene is called glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR), a homodimeric flavoprotein. This enzyme is critical molecule in protecting hemoglobin, red cell enzymes, and biological cell membranes against oxidative stress by increasing the level of reduced glutathione (GSSGR) in the process of aerobic glycolysis; it catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form glutathione (GSH). It also functions as dimeric disulfide oxidoreductase and utilizes an FAD prosthetic group and NADPH to reduce one molar equivalent of GSSG to two molar equivalents of GSH. Defects in this enzyme result in mild to moderately severe hemolytic anemia upon exposure to certain drugs or chemicals. Haemolytic anaemia due to glutathione reductase (GSR) deficiency is extremely rare, characterized by nearly complete absence of GSR activity in erythrocytes. Transmission is autosomal recessive. This disease should be distinguished from glutathione reductase deficiency secondary to dietary riboflavin deficiency and from the acute pharmacologic phenocopy induced by the alkylating agent Carmustine (BCNU) that is used in chemotherapy.