How variations in genes contribute to variations in disease risk has been a subject of study for more than 100 years (IOM, 2006). Until fairly recently research focused on single genes that give rise to rare genetic diseases such as cystic fibrosis or Huntington’s disease. With the advent of genome-wide association (GWA) studies, however, numerous associations between specific gene loci and complex diseases have been identified, for example for breast cancer, type II diabetes, coronary artery disease, asthma, and bipolar disorder (Goldstein, 2009; Hardy and Singleton, 2009; Smith and Lusis, 2009)
