中文摘要：

三染色体性 21，也在症候群下面说出是最经常的 autosomalaneuploidy 和智力迟钝的最普通的原因。百分之五十个病人有先天的心畸形性。20 分钟三染色体性 21 的一个案例出生了，并且发生率是 1in 在中国的 600 ～ 800 个新生儿。在有三染色体性 21 的三分之二个案例中，有自发的流产，因此实际发生比出生后地获得了高。

英文摘要：

Trisomy 21, also named Down syndrome was the most frequent autosomal aneuploidy and the most common cause of mental retardation. Fifty percent patients had congenital heart malformation. Every 20 minutes one case of trisomy 21 was born, and the incidence rate was 1 in 600 to 800 newborns in China.1 In two thirds of cases with trisomy 21, there was a spontaneous abortion, so the actual incidence was higher than that obtained postnatally.