Haplotype analysis in Huntington desease provides insights into mechanisms of CAG repeat expansion
- Univ. of British Columbia, Vancouver (Canada); and others
Huntington disease (HD) is one of 7 disorders now known to be caused by expansion of a trinucleotide repeat. The HD mutation is a polymorphic trinucleotide (CAG) repeat in the 5{prime} region of a novel gene that expands beyond the normal range of 10-35 repeats in persons destined to develop the disease. Haplotype analysis of other dynamic mutation disorders such as myotonic dystrophy and Fragil X have suggested that a rare ancestral expansion event on a normal chromosome is followed by subsequent expansion events, resulting in a pool of chromosomes in the premutation range, which is inherently unstable and prone to further multiple expansion events leading to disease range chromosomes. Haplotype analysis of 67 HD and 84 control chromosomes using 5 polymorphic markers, both intragenic and 5{prime} to the disease mutation, demonstrate that multiple haplotypes underlie HD. However, 94% of the chromosomes can be grouped under two major haplotypes. These two haplotypes are also present in the normal population. A third major haplotype is seen on 38% of normal chromosomes but rarely on HD chromosomes (6%). CAG lengths on the normal chromosomes with the two haplotypes seen in the HD population are higher than those seen on the normal chromosomes with the haplotype rarely seen on HD chromosomes. Furthermore, in populations with a diminished frequency of HD, CAG length on normal chromosomes is significantly less than other populations with higher prevalence rates for HD. These data suggest that CAG length on normal chromosomes may be a significant factor contributing to repeat instability that eventually leads to chromosomes with CAG repeat lengths in the HD range. Haplotypes on the HD chromosomes are identical to those normal chromosomes which have CAG lengths in the high range of normal, suggesting that further expansions of this pool of chromosomes leads to chromosomes with CAG repeat sizes within the disease range, consistent with a multistep model.
- OSTI ID:
- 133358
- Report Number(s):
- CONF-941009--
- Journal Information:
- American Journal of Human Genetics, Journal Name: American Journal of Human Genetics Journal Issue: Suppl.3 Vol. 55; ISSN AJHGAG; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
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