The development of sexual organs in humans is still not completely understood at the molecular level, controlled through the chromosomal difference between men and women. Steroids related to sexual development can have a temporary or permanent effects. Androgens are the leading compounds differentiating between (among other sexual organs) the internal and external genitalia of men. Next to the classical pathway of androgen synthesis (see [https://www.wikipathways.org/index.php/Pathway:WP4523]), alternative pathways are known, which make use of either selective expression patterns of isoenzymes or alternate enzymes. As an alternative, a socalled 'backdoor pathway', which can create dihydrotestosterone (DHT), skipping testosterone. Several enzymes between the classical and backdoor pathway are shared, however the later one utilises one unique enzyme, 3-alpha hydroxysteroid dehydrogenase 3 (gene: AKR1C2). Even though the relevance of this backdoor pathway for humans is not completely clear yet, mutations in the human AKR1C2 gene can lead to disordered sexual differentiation. This finding would indicate that both the classical and the alternative pathway are needed for normal development of male genitalia in humans. For more information on androgens, see Hiort (2013 [https://www.ncbi.nlm.nih.gov/pubmed/23800242]), and for more information on the disease linked to this pathway, please visit Chapter 37 of the book of Blau (ISBN 3642403360 (978-3642403361)). dff bd0 c2a d01 a78 f1d a5a Aka HSD3B2; 3 beta-hydroxysteroid dehydrogenase type II Responsible protein found through Rhea (not part of Blau book) b24 b21 b21 Function:"This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes" [https://www.uniprot.org/uniprot/P16435] c2a ac0 fa0 b21 f1d a5a Function:"Conversion of pregnenolone and progesterone to their 17-alpha-hydroxylated products and subsequently to dehydroepiandrosterone (DHEA) and androstenedione. Catalyzes both the 17-alpha-hydroxylation and the 17,20-lyase reaction. Involved in sexual development during fetal life and at puberty" [https://www.uniprot.org/uniprot/P05093] e32 d30 e32 Function:"This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes" [https://www.uniprot.org/uniprot/P16435] Function:"This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes" [https://www.uniprot.org/uniprot/P16435] Function:"This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes" [https://www.uniprot.org/uniprot/P16435] Function:"This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes" [https://www.uniprot.org/uniprot/P16435] Responsible protein found through Rhea (not part of Blau book) Reduced Reduced Reduced Reduced Reduced Oxidised Oxidised Oxidised Oxidised Oxidised **No Rhea available b21 d30 e32 cc7 d66 fed cc7 ac0 fa0 Specific Rhea for this reaction is not available at the moment; added Rhea for compounds classes reaction **No Rhea available cc7 ac0 fa0 cc7 fa0 c80 fca e64 eda b21 fa8 cc1 a5a fca b21 eda f40 cc7 d66 d50 b21 f1d ff1 acd b21 f1d **No Rhea available aa9 a78 f94 d01 **No Rhea available b21 a5a c80 b21 b21 eda eda eda eda cc7 cc7 f1d a5a 26545797 PubMed 26545797 PubMed Biochemical analyses and molecular modeling explain the functional loss of 17β-hydroxysteroid dehydrogenase 3 mutant G133R in three Tunisian patients with 46, XY Disorders of Sex Development. 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