Pharmacogenomics: the importance of accurate phenotypes.

Lack of knowledge regarding genotype-phenotype correlations is often cited as the major barrier delaying the uptake of pharmacogenomics into routine medical practice. When we look forward to genome-wide association studies as one of the most promising tools for overcoming the pharmacogenomics knowledge barrier, we must keep in mind that having large patient cohorts may not help improve our understanding of alleles implicated in drug-response phenotypes, unless we ensure that such phenotypes are precise and pertinent. It may be wiser, and far more cost effective, to invest scarce research funding in accurate patient drug-response phenotyping than to genotype (or fully sequence) hundreds to thousands of study participants. Biobanks created with personalized medicine research in mind should, when possible, have access to donors' clinical data, including detailed disease- and drug-response phenotypes.