[The use of Bayes theorum in genetic counseling in cases of Duchenne muscular dystrophy].

Bayes' law or theorem (1763) allows the expression of a posterior probability of heterozygosity for an X-linked gene, from two different kinds of information, namely: 1. the prior probability for the mother of an isolated case of Duchenne muscular dystrophy: --to be a carrier by mutation of the gene in one of her parents, or by segregation from earlier generations; --to be herself the origin of the mutation; 2. conditional probabilities, taking into consideration the existence of this woman's normal brothers, sons or maternal uncles and the serum creatine-kinase levels in the possible carrier(s) of the mutant gene. In some situations, these calculations give a recurrence risk which is lower than expected at first and allows sometimes to reassure anxious consultants on their genetic risk.