Abstract
Most common diseases develop through complex interactions among multiple genetic factors and nongenetic （e.g. environmental） factors. Identifying the susceptibility genes has been difficult, because, unlike Mendelian diseases, each causal gene makes a small contribution to the pathogenesis of a disease. Genome wide association study （GWAS） is known as a potentially powerful approach for common complex diseases. Recently, many GWASs have been carried out to detect such causal genes. Here we briefly outline the basic concepts of GWAS and introduce our first experience, from which the PSCA gene was detected as a susceptibility gene of the diffuse type gastric cancer.
