title: [Direct genotypic analysis of myotonic dystrophy: detection of an unstable DNA fragment in carriers].
abstract: BACKGROUND
  Myotonic dystrophy (DM) is an inherited autosomal dominant disorder. The molecular defect responsible for the disease is the expansion of a CTG triplet at the 3' end of the DM gene. We report the analysis of the gene expansion, its correlation with the clinical severity and with the phenomenon of anticipation.
  
  
  METHODS
  Using the cDNA25 probe, we have analyzed 140 affected DM patients from a total of 42 families comprising 303 individuals. According to the clinical status, the affected DM patients were classified as follows: group I, congenital form; group II, classical form, and group III, mild form.
  
  
  RESULTS
  A larger than normal fragment was detected in all the DM patients but in none of the controls. The expansion size is 2.5-6 kb in group I, 0.3-5 kb in group II and 0.2-1.5 kb in group III. In 49 parent-child couples which show clinical anticipation, 47 have an increase in size of the fragment from one generation to the next.
  
  
  CONCLUSIONS
  Our results show a clear correlation between the severity of the disease and the expansion size. We confirm at the molecular level the phenomenon of anticipation. The direct gene analysis of the DM families allows the diagnosis of all the at-risk individuals and facilitates the genetic counselling of these families.
authors.affiliation: Unidad de Genética Molecular, Hospital de la Santa Creu i Sant Pau, Barcelona.
authors.forename: A M
authors.initials: AM
authors.lastname: Cobo
authors.forename: L
authors.initials: L
authors.lastname: Martorell
authors.forename: A
authors.initials: A
authors.lastname: López de Munain
authors.forename: B
authors.initials: B
authors.lastname: Basauri
authors.forename: J M
authors.initials: JM
authors.lastname: Martínez
authors.forename: K
authors.initials: K
authors.lastname: Johnson
authors.forename: M
authors.initials: M
authors.lastname: Baiget
mesh_terms: D000328:Adult; D002648:Child; D004247:DNA / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D009223:Myotonic Dystrophy / Q000235:genetics*; D010375:Pedigree; D012150:Polymorphism, Restriction Fragment Length
chemical_list: D004247:DNA
vernacular_title: Análisis genotípico directo de la distrofia miotónica: detección de un fragmento de ADN inestable en individuos portadores.