The importance of determining the mode of inheritance for the estimation of recurrence risks.

Recurrence risks for the generalised single locus model and for the multifactorial model have been derived and compared. First the areas of overlap for the two models were determined and sets of parameters chosen to represent these overlap areas. Certain sets of parameters for the single locus model give recurrence risks in sibships similar to these for multifactorial inheritance. Other sets (representing very low penetrant dominant genes) give markedly lower risks. Similar results hold for more complex family histories. Empiric risks for families with two or more affected individuals are needed so as to indicate the trend of the increase in risk which could then be extrapolated to other families and be used in genetic counseling.