Deletion of P399_E401 in NADPH cytochrome P450 oxidoreductase results in partial mixed oxidase deficiency

► Mutations in human POR cause congenital adrenal hyperplasia. ► We are reporting a novel 3 amino acid deletion mutation in POR P399_E401del. ► POR mutation P399_E401del decreased P450 activities by 60-85%. ► Impairment of steroid metabolism may be caused by multiple hits. ► Severity of aromatase inhibition is related to degree of in utero virilization.