4. Testosterone Biosynthetic Defects

Testosterone is produced from cholesterol through a number of biochemical conversions. In some individuals, one of the enzymes needed for these conversions is deficient. In such cases, patients are unable to make normal amounts of testosterone despite the presence of testes. Testosterone Biosynthetic Defects affect 46,XY individuals and can be complete or partial, which leads to newborns who appear either completely female or ambiguous, respectively. Four Testosterone Biosynthetic Defects are
listed below:

1. Cytochrome P450,CYP11A Deficiency
2. 3B-Hydroxysteroid Dehydrogenase Deficiency
3. Cytochrome P450,CYP17 Deficiency
4. 17-Ketosteroid Reductase Deficiency

The first three enzyme deficiencies listed above result in Congenital Adrenal Hyperplasia (CAH) (described later) as well as decreased testosterone production by the testes. The fourth enzyme, 17-Ketosteroid Reductase Deficiency, is not associated with CAH. The following chart illustrates the steps of sex differentiation associated with Testosterone Biosynthetic Defects compared to those of unaffected males and females.

Complete Biosynthetic Defect

Partial Biosynthetic Defect