title: Improvement in the molecular diagnosis of Machado-Joseph disease.
abstract: BACKGROUND
  Direct detection of the gene mutation allows for the confirmation of the clinical diagnosis of Machado-Joseph disease (MJD), the most frequent cause of autosomal dominant spinocerebellar ataxia worldwide.
  
  
  OBJECTIVE
  To address the main difficulties in our national MJD predictive testing program. The first was the emergence of intermediate alleles, for which it is not yet possible to determine whether they will cause disease. The second was the issue of homoallelism, ie, homozygosity for 2 normal alleles with exactly the same (CAG)(n) length, which occurs in about 10% of all test results.
  
  
  METHODS
  A large pedigree with 1 affected patient carrying a 71 and a 51 CAG repeat and 2 asymptomatic relatives carrying the 51 CAG repeat and normal-size alleles underwent clinical and molecular studies. Intragenic haplotypes for these alleles were determined. A representative sample of the healthy population in the region was obtained to assess the distribution of the normal (CAG)(n) length. We established the genotype for 4 intragenic polymorphisms in the gene for MJD (MJD1) in 21 homoallelic individuals, to distinguish their 2 normal chromosomes. In addition, we developed a new Southern blot method to completely exclude cases of nonamplification of expanded alleles in the homoallelic individuals.
  
  
  RESULTS
  The study of the family in which the 51 CAG repeat was found suggests that the allele is apparently not associated with disease. These intermediate alleles were not present in a large sample of the healthy population from the same region. Intragenic polymorphisms allowed distinction of the 2 different normal alleles in all cases of homoallelism. The absence of an expanded allele was also confirmed by Southern blot.
  
  
  CONCLUSIONS
  We propose an improved protocol for molecular testing for MJD. These strategies, developed to overcome the practical difficulties mostly in the presymptomatic and prenatal diagnosis of MJD, should prove useful for other polyglutamine-related disorders.
authors.affiliation: UnIGENe, IBMC, Universidade do Porto, 4150-180 Porto, Portugal.
authors.forename: P
authors.initials: P
authors.lastname: Maciel
authors.forename: M C
authors.initials: MC
authors.lastname: Costa
authors.forename: A
authors.initials: A
authors.lastname: Ferro
authors.forename: M
authors.initials: M
authors.lastname: Rousseau
authors.forename: C S
authors.initials: CS
authors.lastname: Santos
authors.forename: C
authors.initials: C
authors.lastname: Gaspar
authors.forename: J
authors.initials: J
authors.lastname: Barros
authors.forename: G A
authors.initials: GA
authors.lastname: Rouleau
authors.forename: P
authors.initials: P
authors.lastname: Coutinho
authors.forename: J
authors.initials: J
authors.lastname: Sequeiros
mesh_terms: D000328:Adult; D000368:Aged; D000483:Alleles; D000067699:Ataxin-3; D001483:Base Sequence; D005260:Female; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D017827:Machado-Joseph Disease / Q000175:diagnosis* / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D010375:Pedigree; D011110:Polymorphism, Genetic / Q000235:genetics; D011174:Portugal; D012097:Repressor Proteins; D019680:Trinucleotide Repeat Expansion
chemical_list: D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; C092341:ATXN3 protein, human; D000067699:Ataxin-3