[Genetic diagnosis of Huntington disease]

We report here a simple and effective method to assess the CAG repeat size of HD gene for gene diagnosis of Huntington disease. Genomic DNA sequences in polymorphic CAG repeat HD gene was amplified by PCR with TaKaRa LA Taq DNA polymerase and GC buffer. To distinguish normal alleles from HD alleles, DNA fragments of affected alleles were recovered as templates for secondary PCR. The secondary PCR products were cloned into T vector for sequencing to determine CAG repeat size. A total of 20 normal individuals and 3 members from a HD pedigree were included in this study. Results showed that the CAG repeat numbers in 20 normal individuals and 3 normal alleles from the HD pedigree varied in normal range, while in 3 HD alleles, the copy numbers of CAG repeat were 39, 40, 41 respectively. There was no overlap between the copy number of the normal and affected alleles. In conclusion, the TaKaRa LA Taq DNA polymerase with GC buffer can be used to effectively amplified CAG repeat of HD gene, which combined DNA sequencing can diagnose HD accurately. In addition, these finding suggested that the dynamic mutation in HD gene responsible for the genetic defect in Chinese HD patients.