[Molecular diagnosis of Huntington's disease: an analysis of two large families].

At present molecular techniques comprise a main resource in the early accurate diagnosis for Huntington's disease. We describe the molecular diagnosis for 8 HD patients and 39 risky family members in two large HD pedigrees by using G8 RFLP linkage analysis as well as direct detection of the expanded (CAG) repeat in IT15 gene with the nested PCR denaturing polyacrylamide gel electrophoretic autoradiography and direct DNA sequencing. The results showed that the normal IT15 alleles contained 13 to 26 CAG repeat but major in 16, while all the HD alleles had over 40 copies of (CAG)n. There was no overlap between the normal and affected alleles. The presymptomatic diagnosis of 39 family members at risk for HD disclosed that 11 subjects carried the affected alleles. All these results indicated that the unstable mutations in IT15 gene were responsible for HD in the Chinese. They also provide valuable data for HD molecular diagnosis, genetic counselling and genetic health.