The inherent value of any disease predictor, however, is a function not just of predictive power, but also the cost and invasiveness of the prediction procedure, and the cost and effectiveness of the interventions available. This balance of practicality and predictive power is central to the incorporation of any predictor to routine medical practice, including genetics. Genetic risk prediction is currently not straightforward, as it requires obtaining a blood or saliva sample and ordering a bespoke genotyping assay for a locus of interest. However, the marginal cost of prediction could be very low in the future if full genome sequences are available and infrastructure is developed to interpret it. The continuing plunge in the cost of sequencing individual genomes (36) is making this scenario increasingly likely. Cheap and readily available genome sequencing is already being used in clinical genetics practice to diagnose genetic disease (37,38), to guide cancer treatment (39) and as a cost-effective form of carrier testing (40). Once a patient's genome is on file, risk prediction can essentially be performed for free and can then be used to inform diagnostics, screening and preventative measures in an automated way.
