We consider the risk of a disease caused by the presence within the genome of one deleterious mutation or two interacting mutations. For an individual, the probability of being mutated/doubly mutated can be estimated knowing the phenotype of the other members in the family pedigree. We study the performance of this process as a function of the size, the shape of the family tree and the parameters of the model. We carry out simulations using the parameters pertaining to breast/ovarian cancer in BRCA-mutated families.