Does the POR rs1057868 TT genotype reduce P450 oxidoreductase activity and lower androgen synthesis?

P450 oxidoreductase (POR) is a vital enzyme that acts as the primary electron donor for microsomal cytochrome P450 enzymes. These enzymes are essential for the biosynthesis of steroid hormones, including androgens (such as testosterone), and the metabolism of many medications. The rs1057868 polymorphism is one of the most significant functional variants of the POR gene.

Biochemical impact and enzymatic activity

Research consistently demonstrates that the POR rs1057868 TT genotype (representing the homozygous *28 or A503V variant) leads to a significant reduction in the POR enzyme's catalytic efficiency.

• Reduced Electron Transfer: Functional biochemical assays show that the TT genotype significantly impairs the enzyme's ability to transfer electrons. In cytochrome c reduction assays, the TT variant exhibited activity of approximately 50.5 units/mg, compared to 135.4 units/mg in the wild-type—a reduction of over 60%.
• Downstream Consequences: This deficit in electron donation directly impacts the performance of several P450 enzymes. For instance, the metabolic activity of CYP2D6 can decrease by 40–50% in the presence of this POR variant, and the metabolic clearance of specific substrates like mitomycin C has been shown to drop from 96.8% in wild-type cells to just 38.3% in those with the TT genotype.

Mechanistic impact on steroidogenesis

The reduction in POR activity has clear implications for the synthesis of steroid hormones.

• Steroidogenic Pathway: POR is a critical requirement for the function of CYP17A1, the enzyme that converts cholesterol derivatives into androstenedione and dehydroepiandrosterone (DHEA), which are the essential precursors for testosterone and other androgens.
• Androgen Synthesis: Because the rs1057868 TT genotype impairs the efficiency of POR, it creates a "bottleneck" in the steroidogenic pathway. This reduced enzymatic support for CYP17A1 leads to less efficient conversion of precursors, thereby lowering the total synthesis of androgens. This mechanism is well-established in research surrounding POR deficiency syndromes, which often manifest with impaired sexual development and adrenal function due to disrupted androgen production.

Bottom line

The claim that the POR rs1057868 TT genotype reduces P450 oxidoreductase activity and lowers androgen synthesis is strongly supported by functional biochemical evidence. The variant significantly reduces electron transfer efficiency, which mechanistically impairs the P450 enzymes required for steroidogenesis, ultimately leading to diminished androgen production.