Fig. 1.

Pathways of DHT synthesis from adrenal DHEA. DHEA is converted by 3β-hydroxysteroid dehydrogenase/isomerase (3βHSD) to AD. In the conventional pathway, AD is first transformed to T (red arrow), which is then converted by SRD5A to DHT. In the alternative pathway, AD is the principal substrate for SRD5A and is converted to 5α-dione (blue arrow), a necessary precursor to DHT. Both 5α-dione and DHT are reversibly interconvertible by 3α-hydroxysteroid dehydrogenases (3αHSD) to the other 5α-reduced steroids, androsterone (AST) and 5α-androstane-3α,17β-diol (Adiol), respectively.