[Clinical characteristics of Huntington disease in two pedigrees and analysis of expanded CAG trinucleotide repeat].

Objective: To understand the clinical and genetic features of Huntington disease (HD).

Methods: The clinical data of HD cases from 2 Chinese families were analyzed and trinucleotide repeat in the IT15 gene were investigated in 9 of the two families by polymerase chain reaction and GeneScan.

Results: Among the two pedigrees, 6 cases were ascertained as HD by genetic test. Genotypes of IT15 were heterozygous in these HD patients. CAG repeat of the patients in the HD chromosome were 40-78. In the two pedigrees, the onset age was earlier in the subsequent generations than that of their fathers. In pedigree 2, the onset age was inversely correlated with CAG repeat number. One out of the 6 cases was juvenile-onset type of Huntington disease, whose clinical symptoms were different from those of the adult-onset cases, especially the hypertonic manifestation.

Conclusion: HD is an autosomal dominant neurodegenerative disorder with genetic anticipation caused by enlargement of CAG repeat in IT15 gene. The clinical manifestation is different between the juvenile-onset and the adult-onset. The number of CAG repeat is inversely correlated with the onset age and clinical severity.