Genetic prediction in Huntington's disease: what are the limitations imposed by pedigree structure?

The major factor limiting use of the polymorphic DNA sequence D4S10, genetically linked to the Huntington's disease (HD) locus, in clinical practice is the fragmented nature of HD families. A population survey in South Wales suggested that genetic prediction would only be possible in 15% of adults at risk as a result of this. We have analysed pedigrees from 151 families, containing 482 adults between 18 and 45 years of age who were at high risk of developing HD, 157 of whom had attended genetic counselling clinics. Thirty-seven percent of adults at high risk in these kindreds had the appropriate pedigree structure needed for presymptomatic testing. It should be possible to perform fetal exclusion tests in about 80% of pregnancies at risk.