The Multifactorial Model for the Inheritance of Liability to Disease and Its Implications for Relatives at Risk

Abstract

The multifactorial model for the inheritance of disease liability (Falconer [1965]) is discussed. In this model, the probability that an individual has the disease depends on the value of some underlying continuous quantity x. The quantity x is assumed to have a genetic component leading to correlations between relatives. For certain family groups, the probabilities of all possible patterns of disease occurrence are shown to be calculable from single integrals involving only univariate Normal density and cumulative distribution functions. Using these probabilities, the recurrence risk for an individual can be calculated from a knowledge of the occurrence of the disease in the family. Relative recurrence risks are tabulated for individuals belonging to families in which there is information on one or both parents, or on two or three full-sibs (or, equivalently, one parent and one or two fullsibs). Recurrence risks in families containing a pair of monozygous twins are also given.