FTO also exemplifies the importance of phenotypic variables. T2D is common in obese individuals. FTO SNPs are associated with T2D, but this is due to the association of T2D and body mass index (BMI). (50) The association of FTO with T2D disappears if T2D cases and controls are matched for BMI. (53) Surprising relationships among phenotypes have also been discovered. For example, SNPs on chromosome 8q24.21 are associated with prostate, breast and colorectal cancer, which were not previously thought to be genetically related.(54) The region contains no known genes, so that without a GWAS strategy, it would have been ignored. It is now being intensively studied.
