Parental origin, nondisjunction, and recombination of the extra chromosome 21 in Down syndrome: a study in a sample of the Colombian population.
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.
Ramírez
Nelson Javier
NJ
Grupo de Neurociencias, Instituto de Genética, Universidad Nacional de Colombia, Bogotá D.C., Colombia.
Belalcázar
Helen Marcela
HM
Yunis
Juan José
JJ
Quintero
Luis Napoleón
LN
Arboleda
Gonzalo Humberto
GH
Arboleda
Humberto
H
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