[IT15 gene analysis in two pedigrees of Huntington's disease].

To investigate the relationship between the clinical features and (CAG)n trinucleotide repeats in two pedigrees of Chinese Huntington's disease (HD). Clinical and neuroimaging features, the age of disease onset and pattern of transmission of the patients were studied in the two pedigrees of HD. Genomic DNA of 42 family members was used for amplification of the (CAG)n repeats of IT15 gene by PCR. The numbers of (CAG)n were determined by electrophoresis through a 6% polyacrylamide gel and direct sequence analysis. Results showed that patients in pedigree 1 were absent of the typical triad of HD symptoms or caudate atrophy. A total of 9 (5 patients and 4 asymptomatic) out of 18 family members had 40-50 (CAG)n repeats in the IT15 gene. In pedigree 2, all the patients were characterized by a triad of symptoms, including motor disturbance, cognitive impairment and psychiatric features. Three patients and two asymptomatic relatives had more than 50 (CAG)n repeats in the IT15 gene. In conclusion, the clinical symptoms are partly determined by (CAG)n repeats in the IT15 gene. The age of onset was correlated with (CAG)n repeats over 50, and the phenomenon called "anticipation" was found to have played a role.