Parental origin, nondisjunction, and recombination of the extra chromosome 21 in Down syndrome: a study in a sample of the Colombian population

introduction. 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. materials and 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.