Journal du syndrome de Down et des anomalies chromosomiques
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Genetic Etiology of Chromosome 21 Nondisjunction and Down syndrome Birth: Aberrant Recombination and Beyond

Sujay Ghosh and Papiya Ghosh

Aberrant recombination pattern is known as risk factor for Chromosome 21 nondisjunction in oocyte and subsequent Down syndrome child birth. A considerable fraction of recombining chromosomes that missegregates exhibits erroneous pattern of single chiasma placement along the length of chromosome 21, either very close to centromere or very close to telomere. This pattern differs significantly from the chromosomes that segregate correctly. Researchers have also found an interaction of maternal age with aberrant pattern of single chiasma positioning on the chromosome and the interaction differs according to stage of meiotic origin of error i.e., meiosis I or meiosis II. Moreover, study on nondisjoined chromosome 21 that carries two simultaneous chiasmata revealed such chromosomes have tendency to missegregate in meiosis II. In meiosis I error double chiasmate chromosome exhibits shifting of distal chiasma towards centromere. Genome wide recombination profiling revealed recombination regulation at the maternal level predisposes meiosis I error, but additional oocyte-specific dysregulation contributes to the nondisjunction event. Very study has characterized certain genomic features that are associated with aberrant recombination pattern of nondisjoined chromosome 21, though confirmation of this notion is contingent to replication of such study in other population.