Is down syndrome hereditary?

[Yuwan]

Hello, is down syndrome hereditary? If two people who have down syndrome gets married will their kids also have down syndrome? Please let me know is it hereditary? What will happen if my brother with down syndrome marries someone who has down syndrome? Will their kids also have down syndrome?

[Hua]

@yuwan Hello, No in most cases it is not hereditary. It's caused by a mistake in cell division during the early development of the fetus. Translocation Down syndrome can be passed from parent to child. However, only about 3 to 4 percent of children with Down syndrome have translocation and only some of them inherited it from one of their parents.