The ability to stratify patients and their disease by understanding the genetic basis of their disorders is a very powerful paradigm for drug discovery and development. All the phenotypic tests that have been developed are all a consequence to some extent of the genetics of the patient. The biomarker literature is littered with false associations owing to small sample sizes and inadequate controls. In contrast, the analysis of inherited disease by the application of both Mendelian genetics and association studies with very large data sets has led to very robust findings. In other words, “Genetics never lies”. This important fact has driven, and will continue to drive, novel drug discovery, development and patient stratification. There are good examples for using somatic cell genetics for drug discovery in oncology (leading to crizotinib and vemurafinib) that are showing the way. The same concept applies to other diseases such as multiple sclerosis and amyotrophic lateral sclerosis. But it is more difficult.