What causes Down syndrome?

What causes Down syndrome?

Each human cell typically contains 23 pairs of chromosomes. Down syndrome occurs because of changes in the way cells in chromosome 21 divide. Every person with Down syndrome has an extra amount of this chromosome in some or all of their cells.

In the most common type of Down syndrome, trisomy 21, the condition occurs randomly and isn’t inherited. However, when translocation or mosaicism is the cause of Down syndrome, hereditary (passed down among family members) should be looked at as a cause.