title: Parental origin, nondisjunction, and recombination of the extra chromosome 21 in Down syndrome: a study in a sample of the Colombian population.
abstract: BACKGROUND
  Free trisomy 21 is responsible for 95% of Down syndrome cases. Advanced maternal age and susceptible recombination patterns are recognized risk factors associated to Down syndrome. Maternal origin of trisomy occurs in approximately 90% of cases; paternal and mitotic origin share the remaining 10%. However, the recombination events that serve as a risk factors for trisomy 21 have not been carefully characterized.
  
  
  OBJECTIVE
  To analyze and validate observations in a sample of Colombian trysonomy 21 cases.
  
  
  METHODS
  Twenty-two Colombian families were selected, each with one affected Down syndrome (free trisomy 21) child. Microsatellite polymorphisms were used as DNA markers to determine the parental/stage origin of non-disjunction and recombination events. Non-parametric tests were used to compare our results with those reported. Multiple correspondence analysis was used to outline different groups and their associations.
  
  
  RESULTS
  Distribution of trisomy 21 was 90.9% maternal, 4.5% paternal and 4.5% from mitotic origin, similar to distributions reported previously. However, we found differences in the frequency of maternal meiotic stage errors between the present study (46.1% meiosis I and 53.9% meiosis II) compared to those reported previously (70% meiosis I and 30% meiosis II). Multiple correspondence analyses showed association of either local recombination events or absence of recombination with specific non-disjunction stages.
  
  
  CONCLUSIONS
  Recombination patterns found in this study support the hypothesis that susceptible chiasmate configurations are associated to maternal meiosis I and meiosis II errors. Non-disjunction frequencies between maternal meiotic stages need to be clarified in our population.
authors.affiliation: Grupo de Neurociencias, Instituto de Genética, Universidad Nacional de Colombia, Bogotá D.C., Colombia.
authors.forename: Nelson Javier
authors.initials: NJ
authors.lastname: Ramírez
authors.forename: Helen Marcela
authors.initials: HM
authors.lastname: Belalcázar
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Yunis
authors.forename: Luis Napoleón
authors.initials: LN
authors.lastname: Quintero
authors.forename: Gonzalo Humberto
authors.initials: GH
authors.lastname: Arboleda
authors.forename: Humberto
authors.initials: H
authors.lastname: Arboleda
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002891:Chromosomes, Human, Pair 21 / Q000235:genetics*; D003105:Colombia; D004314:Down Syndrome / Q000235:genetics*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009630:Nondisjunction, Genetic; D010290:Parents; D011995:Recombination, Genetic