Clinical and genetic study of a juvenile⁃onset Huntington disease

Abstract

Background Huntington's disease (HD) is an autosomal dominant hereditary progressive neurodegenerative disorder with a distinct phenotype characterized by chorea, dementia, cognitive and affective impairment. There are selective neural cell loss and atrophy in the caudate and putamen. Dr. George Huntington firstly described the disease accurately and insightfully, which led to a widespread recognition of the inherited chorea that now bears his name. Huntington disease gene (IT15) locus on chromosome 4p16.3, and encompasses 67 exons with a trinucleotide repeat (CAG) in the first exon. The CAG repeat length is highly polymorphic in the population and expanded on at least one chromosome of individuals with HD. Clinically, patient with HD are often onset in adulthood. Juvenile⁃onset HD is relatively rare. Adult⁃onset HD patients usually have a CAG expansion from 40 to 55 whereas those with juvenile ⁃ onset greater than 60 which are often inherited from the father. We investigated the clinical features of a juvenile⁃onset case with Huntington disease and dynamic mutation of his family. Methods The CAG repeats of IT15 gene were detected using polymerase chain reaction and capillary electrophoresis in 115 individuals with preliminary diagnosis as Huntington disease. The repeat numbers of some samples carried expanded or intermediate alleles were verified by the pMD18⁃T vector clone sequencing. Results Fragment analysis showed that one juvenile ⁃ onset case presenting with cognitive dysfunction and hypokinesis carried 15/68 CAG repeats of IT15. His father carried 17/37 and mother carried 15/17. Conclusion 1) The juvenile ⁃onset case of HD presented with different clinical features compared with adult⁃onset cases. The typical signs of adult⁃onset cases include progressive chorea, rigidity and dementia. The most common sign of juvenile⁃onset Huntington disease is cognitive decline. 2) The dynamic mutation of IT15 gene expansion of the CAG repeats in the intergenerational transmission may lead to anticipation, which is a phenomenon characterized by increasing severity and earlier onset in successive generations. The abnormal allele of the patient inherited from his father and substantially expanded between generations, which indicates the CAG repeats is more unstable in the paternal inheritance.

DOI：10.3969/j.issn.1672⁃6731.2012.03.011