Genetic analysis of frequencies of phenotypes in the spontaneously diabetic BB rat--a main animal model of autoimmune type-I-diabetes.

The incidence of diabetes shows variations of 40 to 80% in different BB rat sublines. Whether genetic or environmental factors are responsible for this observation remains unclear. Little data is available on population-based investigations and no results have been reported about computer-aided simulation of models with regard to the inheritance of spontaneous diabetes in BB rats. On the basis of the finding that diabetes incidence in offspring of diabetic parents is significantly higher than in matings in which one or both parents were non-diabetic we have analysed the frequencies of parental phenotypes in relation to the incidence of diabetes over 25 inbred generations in our BB/OK rat strain. We could ascertain a relation of a high frequency of matings of diabetic parents to high diabetes incidence. This was confirmed by model-based simulations and comparison of simulated and observed diabetes incidence. The study gives strong evidence of segregation of one additional gene in the BB/OK rat subline.