Resumen
- Down Syndrome (DS) is the most common trisomy in human beings. Its incidence is estimated in one of 745 live births. On a global scale, it is the most frequent cause of mental retardation. The origin of this trisomy is due to a meiotic non-disjunction in about 95% of cases and is usually maternal, especially in women above 35 years of age. The remaining 5% is due to errors in post-zygotic mitosis. Objective: identify the parental origin of the extra chromosome 21, when the error is not disyuncional and establish a correlation between these events and phenotypic manifestations of the patients affected. Materials and methods: we studied fifty families with a child with DS, using 5 STRs markers along 21q which allowed identification of the origin of chromosome 21 additional parents, the time when the error occurred and recombination presents. The statistical analysis was done using the package SPSS version 15.0 for Windows. Results: in 80% of households in the error was meiosis I and 20% in meiosis II, 98% of the additional chromosomes was home maternal and paternal 2% similar to those reported by other authors, correlation was found genotype-phenotype characteristics studied at 8, neck short and wide, third fontanel, prominent lower lip, palate narrow and short, crossing hélix root of the shell, alopecia, single palm crease and other anomalies as nevi and xeroderma and recombination events in 24,5% of the families tested. Conclusions: the maternal age and variation in the number of recombination is not associated with disjunctions meiotics I and II genotype phenotype correlation was found, but the sample size should be expanded in order to establish with certainty that the correlations.