Nature Genetics
4, 221 - 226 (1993)
doi:10.1038/ng0793-221
Expansion of an unstable trinucleotide CAG repeat in spinocerebellar ataxia type 1Harry T. Orr1, Ming-yi Chung1, Sandro Banfi2, Thomas J. Kwiatkowski Jr.3, Antonio Servadio2, Arthur L. Beaudet3, 4, Alanna E. McCall2, Lisa A. Duvick1, Laura P. W. Ranum1
& Huda Y. Zoghbi2, 3
1Department of Laboratory Medicine and Pathology and Institute of Human Genetics, University of Minnesota, Minneapolis, Minnesota 55455, USA
2Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA
3Institute for Molecular Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
4Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030, USA Correspondence should be addressed to H.Y.Z. Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant disorder characterized by neurodegeneration of the cerebellum, spinal cord and brainstem. A 1.2−Megabase stretch of DNA from the short arm of chromosome 6 containing the SCA1 locus was isolated in a yeast artificial chromosome contig and subcloned into cosmids. A highly polymorphic CAG repeat was identified in this region and was found to be unstable and expanded in individuals with SCA1. There is a direct correlation between the size of the (CAG)n repeat expansion and the age−of−onset of SCA1, with larger alleles occurring in juvenile cases. We also show that the repeat is present in a 10 kilobase mRNA transcript. SCA1 is therefore the fifth genetic disorder to display a mutational mechanism involving an unstable trinucleotide repeat.
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