SNP selection and genotyping

CBR1 rs3787728 and rs2835267 were selected according to a previous study (17). Genomic DNA was extracted from whole blood using the AxyPrep Blood Genomic DNA Miniprep kit (Axygen Scientific, Inc., Union City, CA, USA). The two CBR1 SNPs were then genotyped using Sequenom Mass Array matrix-assisted laser desorption ionization-time of flight mass spectrometry platform (Sequenom, San Diego, CA, USA). The polymerase chain reaction and single base extension primers were designed using Assay Design software version 3.0 (Sequenom) and synthesized by Sangon Biotech Co., Ltd. (Shanghai, China). The primers were as follows: rs3787728 forward, 5′-ACGTTGGATGATTTCCAGAGGATCCCTATC-3′; reverse, 5′-ACGTTGGATGTGACCTGCAGGATCCTGGTG-3′; extension, 5′-CCTTTTCCCTAAGTCGT-3′; rs2835267 forward, 5′-ACGTTGGATGACCTTTCAGTAGGGCTGTTC-3′; reverse, 5′-ACGTTGGATGCTAGCACTTGAGAATACCAG; extension, 5′-ACAGACACCAGAAAACAA-3′.