Rs7439366

rs7439366, also known as Y268H, is a SNP in the UGT2B7 gene encoding the 2B7 UDP-Glucuronosyltransferase, active primarily in the liver. The rs7439366(C) allele encodes a histidine (H) at amino acid 268, and the (T) allele encodes a tyrosine (Y). Most publications refer to the histidine as the wild-type (more common) allele.

In a study of glucuronidation activity of human livers, rs7439366(T;T) individuals had 28% lower activity than rs7439366(C;C) individuals with respect to O-glucuronidation of tamoxifen metabolites 4-OH-tamoxifen and endoxifen. The authors suggest this may help explain interindividual variability (beyond CYP2D6 variation) in tamoxifen metabolism - and therefore the effectiveness of tamoxifen in reducing breast cancer recurrence.