[Use of polymorphous DNA probes in the study of French families with Huntington's chorea].

Huntington disease (HD) is a neurodegenerative disorder caused by an autosomal dominantly inherited defect. The discovery of DNA polymorphisms genetically linked to the HD locus provided the possibility of an early presymptomatic test. The first marker locus described (G-8) had an approximately 5% recombination rate with the HD locus, and the subsequent discovery of some more tightly linked marker loci, notably D 495, has greatly improved the accuracy of presymptomatic testing. We describe here the preliminary results obtained and the difficulties encountered in a French predictive testing program on presymptomatic subjects belonging to choreic families.