Prediction of genetic risks from segregation analyses of morbid risks

Segregation analysis provides a genetic model of disease based upon morbid risks in age-specific classes, from which the model derives genotype-specific morbid risks. In the absence of disease-specific mortality each morbid risk is a cumulative incidence (age-specific penetrance). If disease-specific mortality reduces the number of affected in the older classes, the morbid risk is less than the corresponding penetrance. When counselling individuals with a family history of disease, their genetic risk is a function of penetrances, which can be calculated from morbid risks. We have applied this method to breast, ovarian and colorectal cancer.