Isabel Silveira

Publications (2)5.07 Total impact

• Article: Linkage disequilibrium analysis in Machado-Joseph disease patients of different ethnic origins

  Claudia Gaspar, Iscia Lopes-Cendes, Anita L. DeStefano, Patrícia Maciel, Isabel Silveira, Paula Coutinho, Patrick MacLeod, Jorge Sequeiros, Lindsay A. Farrer, G. A. Rouleau
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  ABSTRACT: Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar degeneration originally described in families of Portuguese-Azorean ancestry. The hypothesis that its present world distribution could result from the spread of an original founder mutation has been raised. To test this possibility we have conducted a linkage disequilibrium study of markers segregating with the MJD1 locus in a total of 64 unrelated families of different geographical origins. Significant association was detected between the MJD1 locus and marker alleles at loci D14S280, D14S1050 and D14S81. All affected individuals, except one Chinese family, had allele 3 (237 bp) at D14S280. This finding is consistent with a founder effect in our MJD population. However, distinct haplotypes were observed in patients originating from the two Azorean islands showing the highest disease prevalence; therefore, the possible existence of more than one founder mutation can not be excluded with the markers currently available.
  Human Genetics 08/1996; 98(5):620-624. · 5.07 Impact Factor
• Article: Correlation between CAG Repeat Length and Clinical Features in Machado-Joseph Disease

  Patrícia Maciel, Claudia Gaspar, Anita L DeStefano, Isabel Silveira, Paula Coutinho, João Radvany, David M. Dawson, Lewis Sudarsky, João Guimarães, Jose E. L. Loureiro, Marjan M. Nezarati, Lee I. Corwin, Iscia Lopes-Cendes, Karen Rooke, Roger Rosenberg, Patrick MacLeod, Lindsay A Farrer, Jorge Sequeiros, Guy A Rouleau
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  ABSTRACT: Machado-Joseph disease (MJD) is associated with the expansion of a CAG trinucleotide repeat in a novel gene on 14q32.1. We confirmed the presence of this expansion in 156 MJD patients from 33 families of different geographic origins: 15 Portuguese Azorean, 2 Brazilian, and 16 North American of Portuguese Azorean descent. Normal chromosomes contain between 12 and 37 CAG repeats in the MJD gene, whereas MJD gene carriers have alleles within the expanded range of 62–84 CAG units. The distribution of expanded alleles and the gap between normal and expanded allele sizes is either inconsistent with a premutation hypothesis or most (if not all) of the alleles we studied descend from a common ancestor. There is a strong correlation between the expanded repeat size and the age at onset of the disease as well as the clinical presentation. There is mild instability of the CAG tract length with transmission of the expanded alleles; both increase and decrease in size between parents and progeny occur, with larger variations in male than in female transmissions. Together, these effects can partly explain the variability of age at onset and of phenotypic features in MJD; however, other modifying factors must exist.