[Multivariate approach to calculating the recurrence risk in families with multifactorial diseases].

To resolve one of the main theoretical problems of genetic counselling, namely, calculation of the recurrence risk for common diseases, a multivariate approach is suggested, based on the multifactorial model. The model suggests partially different liability for several diseases or various forms of a disease. The specified recurrence risk for each family can be calculated with the account of different morbidity rates for different sexes and the degree of kinship to proband. The input data for computer calculations are: population incidence of diseases, their heritabilities as well as genetical and environmental correlations between the diseases. Our method is illustrated by calculation of the recurrence risk for diabetes mellitus (DM) and bronchial asthma (BA), each of which may be subdivided into several forms. It is proposed that the nature of genetic correlations is different for two diseases. The phenotypic forms of DM are genetically independent, whereas the forms of BA have a common genetic basis.