Environmental risk factors can be added to the genetic predictor, to make a better predictor of the phenotype. In practice not all environmental factors are identified (and some factors classified as “environment” may simply be stochastic events12). For example, combining SNPs and phenotypic predictors, such as body-mass-index and smoking, improved prediction of age-related-macular degeneration, an eye disease in humans where age is a major risk factor13. In some circumstances more accurate phenotyping, including the use of repeated measures, can lead to a more heritable trait. In general, expectations need to be adjusted accordingly for the application of phenotype or disease prediction in humans.
