The activities of 5α-reductase and 17,20-lyase determine the direction through androgen synthesis pathways in patients with 21-hydroxylase deficiency

► We examined the activities of the 5α-reductase and 17,20-lyase in patients with 21-hydroxylase deficiency. ► We used urinary steroid metabolomics obtained by gas chromatography - mass spectrometry. ► The 5α-reductase is the gatekeeper of the backdoor pathway. ► The 17,20-lyase is the regulator of the flux through the androgen pathways.