Blood processing, DNA extraction, and genotyping: Blood samples will be drawn into ethylenediamenetetraacetic acid (EDTA) tubes and immediately refrigerated at 4° C. Plasma will be separated by centrifugation and stored at -80° C. DNA will be extracted from the buffy coat using a commercially available kit (Qiagen Puregene, Valencia, California) and stored at -20° C. Study participants will be genotyped for three common chr4q25 SNPs (rs2200733, rs17570669, and rs3853445) using Sanger sequencing.