Estimation of the proportion of genetic cases in late-onset diseases: an application to Alzheimer's disease.

In diseases with a complex etiology including a genetic component, an important issue is to determine the proportion of cases really having inherited the disease. This is not easy in late-onset diseases where censoring might obscure the transmission pattern of the disease and give an apparently non-genetic distribution of the cases. We present a model that allows the estimation of the proportion of genetic cases in late-onset diseases. This model takes censoring into account by explicit modelling of the time dependency of the onset of the disease. The model is illustrated with an example based on an epidemiological survey in Alzheimer's disease and with simulated data.