Predictive testing for Huntington's disease with linked DNA markers.

Availability of new DNA markers, more tightly linked to the Huntington's disease (HD) locus than the original G8 (D4S10) probes, has improved predictive accuracy for both presymptomatic and prenatal exclusion testing. 50 predictive tests were carried out on high-risk individuals. 6 of these were on first-trimester chorionic villus biopsy specimens; in 2 cases the HD gene was not transmitted to the fetus while in 4 cases no exclusion could be made. The remaining 44 tests were on adults with either 25 or 50% risk of manifesting the disease; 19 had a greatly increased risk and 25 a substantially decreased risk of HD. Family structures in Scotland are suitable for testing about 75% of potentially affected individuals, and the new generation of DNA markers makes virtually all families fully informative.