What causes down syndrome?

Down syndrome is caused by the presence of an extra copy of chromosome 21 in a person's cells. This extra genetic material disrupts the normal course of development, leading to the physical and cognitive characteristics associated with Down syndrome. The exact reason why this extra chromosome occurs is not fully understood, but it is known to be a random genetic event that can happen during the formation of reproductive cells or early in fetal development.

Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. This can happen in a few different ways:

- Nondisjunction: This is the most common cause of Down syndrome. It occurs when there is an error in cell division during the formation of the egg or sperm. This can result in an egg or sperm that has an extra copy of chromosome 21.
- Translocation: This occurs when a piece of chromosome 21 breaks off and attaches to another chromosome, typically chromosome 14. This can result in a child who has two copies of chromosome 21 on one chromosome and one copy on the other.
- Mosaicism: This is a less common cause of Down syndrome. It occurs when some cells in the body have an extra copy of chromosome 21 while other cells do not. This can result in a child who has some of the features of Down syndrome, but not all of them.