Problems in genetic counseling in a family with an "atypical" centronuclear myopathy

Genetic counseling often deals with a rare disease the inheritance of which is not clearly established or in which genetic heterogeneity is reported. In addition, relevant parameters such as penetrance, gene frequency, and mutation rate may not be available. In this situation, establishing the risk may be very difficult. An example is presented in which Bayesian risk calculation proved to be of great help in providing precise risk estimates in a family in which an "atypical" centronuclear myopathy was segregating.