2.3. Sample collection, DNA extraction, single‐nucleotide polymorphism selection, and genotyping

We collected 2 ml venous blood in ethylenediaminetetraacetic acid anticoagulant tubes. DNA was extracted using a HiPure Blood DNA Mini Kit (Magen, China) according to the manufacturer's protocols. Extracted DNA was stored at −20℃.

Thirteen tagSNPs from GRIN1, GRIN2A, and GRIN2B were selected. All SNPs met the following criteria: (1) a minor allele frequency (MAF) > 5% in the Chinese Han population, (2) SNPs were selected by Haploview (version 4.2) using pairwise linkage disequilibrium with default settings (the Hardy–Weinberg P value cutoff was 0.05 and r² > 0.8).

Assay Designer software (version 3.1) was used for the selected SNP primer design. Polymorphisms were detected using the Sequenom MassARRAY Genotype Platform (Sequenom, San Diego, California, USA) using an allele‐specific matrix‐assisted laser desorption ionization–time of flight mass spectrometry method.