[Genetic counseling on a molecular basis for Huntington's chorea].

The gene responsible for Huntington Disease has been mapped at the end of the short arm of chromosome 4. Different polymorphic probes from the immediate vicinity of the gene are available and provide accurate tools for the identification of carriers of the gene. The presymptomatic testing of adults or the prenatal testing (exclusion testing) of the unborn child must be considered with great caution, it requires a multidisciplinary approach and will benefit from intensive collaboration with the lay organizations. Presymptomatic testing will presumably find a much wider application when it can be coupled to an effective preventive treatment.