Fig. 2

Schematic overview situating the studied genes within the different branches of the steroidogenesis pathway. CYP11A1 encodes the first and rate-limiting enzyme in the steroidogenic pathway. FDX1, FDX2 and FDXR encode ferredoxin (also called adrenodoxin) and ferredoxin reductase which are involved in electron transfer to CYP11A1. HSD3B1 and HSD3B2 encode the 3β-hydroxysteroid dehydrogenases that are involved in the synthesis of sex steroids, aldosterone and cortisol. CYP17A1 encodes the enzyme catalysing the next step towards sex steroid production and POR, CYB5A and CYB5B encoding P450 oxidoreductase and cytochrome b5 are needed as mediators of electron transport to CYP17A1 for its 17,20-lyase activity. HSD17B1, HSD17B2, HSD17B3, HSD17B6, HSD17B7, HSD17B8, HSD17B10, HSD17B11, HSD17B12 and HSD17B14 encode several 17β-hydroxysteroid dehydrogenases and are a group of enzymes that mainly catalyse the interconversion of dehydroepiandrosterone <—> androstenediol, androstenedione <—> testosterone, and estrone <—> estradiol, with enzyme-specific substrate specificity/preferential direction of the reaction (see Additional File 1 Table A1). CYP19A1 encodes aromatase which is responsible for the conversion of male to female sex hormones. CYP21A2 encodes 21-hydroxylase and CYP11B1 encodes 11β-hydroxylase that are required for the synthesis of both aldosterone and cortisol. CYP11B2 encodes 11β-hydroxylase which is committed to the final steps of aldosterone synthesis. SULT2A1, SULT2B1, SULT1E1 encode enzymes responsible for sulphation of steroids and STS encodes steroid sulphatase