CYP21A2 and familial glucocorticoid deficiency: However, overall Cyp21a2-deficient mutants showed some residual ability to synthesize cortisol and on a systemic level were less glucocorticoid deficient than our model of glucocorticoid deficiency caused by disruption of the mitochondrial redox cofactor to steroidogenesis ferredoxin 1b (fdx1b) (18).