the Population Architecture using Genomics and Epidemiology (PAGE) study sites. After several quality control and data organization steps, either the standard logistic or linear regression analysis is performed depending on the phenotypic information. Subsequently, all continuous phenotypes are log-transformed before the association between the SNPs and the transformed phenotypes is finally calculated. Generally, there are two types of results from a PheWAS study: A result can be considered 'expected' if a genotype-phenotype association has previously been observed and reported. These cases can validate the legitimacy of PheWAS and act as a positive control. For instance, diabetes-related phenotypes like hyperinsulinemia, obesity, and fasting glucose level are shown to be associated with phenotypes of type II diabetes from PheWAS. A 'novel' result would be of more interest since it demonstrates the power of PheWAS for discovering new associations that have not been reported before. If two disease phenotypes are not previously-known as related and a single SNP is shown to give rise to these two phenotypes, it is a good indication that a pleiotropic effect is present. An example of this pleiotropic discovery is a SNP that's already known to be associated with diabetes turns out to also be significantly associated with arthritis. Even though novel associations between phenotype is discovered, further biological studies is necessary to determine whether it actually reflects the system. Drug Response Variability A PheWAS has also successfully highlights discrepancies in drug response among individuals. A quantitative PheWAS study was done to identify variation in thiopurine response. The EMR stores quantitative value of IBD patient's TPMT (thiopurine S-methyltransferase) activity, which then allow researchers to split the patients it into three categories: low TPMTa, normal TPMTa, and very high TPMTa. It was found that cohorts with very high TPMTa level are associated with diabetes mellitus and iron-deficiency anemia, which further shows that thiopurine therapy are three times more likely to fail in patients with very high TPMTa. Performing thiopurine therapy on patient with very high TPMTa level may increase the frequency of anemia episode. This PheWAS finding may further the progress of personalized treatment based on patient's measurement. Instead of treating IBD patients with the conventional thiopurine treatment, patient may benefit more from more intensive therapy or other approaches. Clinical Significance A clinical test has been done by utilizing PheWAS on HIV patients, obtained from the AIDS Clinical Trial Group (ACTG) datasets from 27 different laboratories. Identifying accuracy between