CYB5R3 and hereditary disease: Congenital methemoglobinemia is caused by gene mutation to decrease the activity or stability of NADH-Cytochrome b5 reductase (b5R),[4] The formation of autosomal recessive genetic disease mainly characterized by methemoglobin (MetHb) reduction disorder.[5,6] There are 2 clinical types: Type I, also known as erythrocyte type, is characterized by decreased stability of b5R, and its clinical manifestations are closely related to the content of MetHb.