Cytochrome b5 deficiency

Cytochrome b 5 deficiency is a rare condition and form of isolated 17.20-lyase deficiency caused by deficiency in cytochrome b 5, a small hemoprotein that acts as an allosteric factor to facilitate the interaction of CYP17A1 with P450 oxidoreductase, 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 b 5 is reduction of methemoglobin, so cytochrome b 5 deficiency can also result in elevated methemoglobin levels and/or methemoglobinemia, similarly to deficiency of cytochrome b 5 reductase.