trisomy 18 syndrome

例句：

1. 1.This child has a genetic disorder that is caused by having an extra copy of chromosome 18.
   这个孩子患有一种遗传病，是由于染色体18多出一条造成的。
2. 2.The trisomy 18 syndrome is the most common cause of mental retardation in children.
   唐氏综合症是儿童智力低下最常见的原因。
3. 3. Trisomy 18 syndrome can lead to physical and developmental disabilities, including heart defects and learning difficulties.
   唐氏综合症可能导致身体和发育上的障碍，包括心脏缺陷和学习困难。