Down综合征(DS)是智力低下最常贝的原因,96%以上的病例是由于不分离导致21三体。尽管三十年前发现此病,但有关双亲之一配子影响额外染色体发生的因素知道的却很少。已提出有关发病机理的几种假说,如双亲嵌合体、涉及21号染色体的随体联合、NOR区域活性、未成熟着丝粒分裂、减数分裂时21号染色体不配对或不分离的遗传倾向等。 Down syndrome (DS) is the most common cause of mental retardation, with more than 96% of cases due to nondeletion leading to trisomy 21. Although the disease was discovered 30 years ago, little is known about the factors that affect the appearance of extra chromosomes by one of the parents. Several hypotheses regarding the pathogenesis have been proposed, such as the genetic relationship between the parental chimera, the satellite association involving chromosome 21, the activity of the NOR region, immature centromere division, chromosome 21 unpaired or not at meiosis Wait.