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      Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats.

      Nature genetics

      Trinucleotide Repeats, genetics, Transcription Factors, TATA-Box Binding Protein, Spinocerebellar Degenerations, Repetitive Sequences, Nucleic Acid, Proteins, Nerve Tissue Proteins, Molecular Sequence Data, Middle Aged, Male, Humans, Gene Expression Regulation, Female, immunology, DNA-Binding Proteins, Cloning, Molecular, Child, Base Sequence, Antibodies, Monoclonal, Amino Acid Sequence, Alleles, Age of Onset, Adult, Adolescent

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          Abstract

          Two forms of the neurodegenerative disorder spinocerebellar ataxia are known to be caused by the expansion of a CAG (polyglutamine) trinucleotide repeat. By screening cDNA expression libraries, using an antibody specific for polyglutamine repeats, we identified six novel genes containing CAG stretches. One of them is mutated in patients with spinocerebellar ataxia linked to chromosome 12q (SCA2). This gene shows ubiquitous expression and encodes a protein of unknown function. Normal SCA2 alleles (17 to 29 CAG repeats) contain one to three CAAs in the repeat. Mutated alleles (37 to 50 repeats) appear particularly unstable, upon both paternal and maternal transmissions. The sequence of three of them revealed pure CAG stretches. The steep inverse correlation between age of onset and CAG number suggests a higher sensitivity to polyglutamine length than in the other polyglutamine expansion diseases.

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          Most cited references 50

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          An analysis of 5'-noncoding sequences from 699 vertebrate messenger RNAs.

          5'-Noncoding sequences have been compiled from 699 vertebrate mRNAs. (GCC) GCCA/GCCATGG emerges as the consensus sequence for initiation of translation in vertebrates. The most highly conserved position in that motif is the purine in position -3 (three nucleotides upstream from the ATG codon); 97% of vertebrate mRNAs have a purine, most often A, in that position. The periodical occurrence of G (in positions -3, -6, -9) is discussed. Upstream ATG codons occur in fewer than 10% of vertebrate mRNAs-at-large; a notable exception are oncogene transcripts, two-thirds of which have ATG codons preceding the start of the major open reading frame. The leader sequences of most vertebrate mRNAs fall in the size range of 20 to 100 nucleotides. The significance of shorter and longer 5'-noncoding sequences is discussed.
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            • Record: found
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            CAG expansions in a novel gene for Machado-Joseph disease at chromosome 14q32.1.

            We have identified a novel gene containing CAG repeats and mapped it to chromosome 14q32.1, the genetic locus for Machado-Joseph disease (MJD). In normal individuals the gene contains between 13 and 36 CAG repeats, whereas most of the clinically diagnosed patients and all of the affected members of a family with the clinical and pathological diagnosis of MJD show expansion of the repeat-number (from 68-79). Southern blot analyses and genomic cloning demonstrates the existence of related genes. These results raise the possibility that similar abnormalities in related genes may give rise to diseases similar to MJD.
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              • Record: found
              • Abstract: found
              • Article: not found

              Expansion of an unstable trinucleotide CAG repeat in spinocerebellar ataxia type 1.

              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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                Author and article information

                Journal
                8896557
                10.1038/ng1196-285

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