[DNA diagnosis of Huntington's chorea. Application and genetic counseling in 4 involved families].

The discovery of linked DNA markers permits presymptomatic and prenatal diagnosis of autosomal-dominant Huntington's disease. However, family members born at 50% risk can find out if they have inherited the mutant gene only if family analyses are possible. Many individuals at risk lack a sufficient number of living relatives for presymptomatic testing. However, prenatal exclusion testing in pregnancy can be offered to most probands. In four case reports we demonstrate the first clinical use of these markers for genetic counselling in Switzerland. The method was used for both presymptomatic testing and prenatal diagnosis. Prenatal exclusion testing is described in one family. The general practitioner should be informed of the potentialities of DNA technology, since competent advice to his patients and follow-up of positive probands are part of his duties.