Cytochrome B5 Deficiency

Cytochrome b₅ deficiency is a rare condition and form of isolated 17,20-lyase deficiency caused by deficiency in cytochrome b₅, a small hemoprotein that acts as an allosteric factor to facilitate the interaction of CYP17A1 (17α-hydroxylase/17,20-lyase) with P450 oxidoreductase (POR), thereby allowing for the 17,20-lyase activity of CYP17A1. The condition affects both adrenal and gonadal androgen biosynthesis and results in male pseudohermaphroditism. The principal biological role of cytochrome b₅ is reduction of methemoglobin, so cytochrome b₅ deficiency can also result in elevated methemoglobin levels and/or methemoglobinemia, similarly to deficiency of cytochrome b₅ reductase (methemoglobin reductase).