*2.2. Quality Control*

Genotype quality control (QC) procedures were performed using PLINK v1.90 [26]. To consider the accuracy and efficiency of SNP genotyping, valid genotypes for each SNP were determined by setting a cut-off of 0.5 for the GenCall (GC) and GenTrain (GT) scores [27]. Samples that did not meet the quality criteria (missing genotype call rate 0.1) were eliminated from the analysis.

After merging the genotypic data from the 600K and 50K arrays, a total of 42,230 autosomal SNPs that overlapped between the two DNA chips were left in the analysis. SNPs with a call rate below 0.90, a minor allele frequency (MAF) lower than 0.05, or those which were located on sex chromosomes were eliminated from the analysis.
