Rs1057868

rs1057868, also known as A503V, is a relatively common variant defining the POR*28 allele of the P450 (cytochrome) oxidoreductase POR gene. The POR gene encodes a protein involved in electron transport of cytochrome p450 enzymes such as CYP3A4, CYP3A5 and CYP3A7.

A study of 251 individuals from two independent studies (182 patients treated with methadone and 69 patients with clozapine) for CYP3A activity found that CYP3A SNPs themselves did not predict particularly well inter-individual variability in overall CYP3A activity. However, rs1057868(T;T) individuals had a 1.6x increased CYP3A activity compared to rs1057868(C) carriers (n=182, p=0.004), and the finding was replicated in a second independent dataset. The authors conclude that this POR gene SNP is a better predictor of overall CYP3A activity than CYP3A SNPs.