Trisomies
Our cells usually have 23 pairs of chromosomes. Trisomy is the word used to describe the presence of an extra chromosome in the cells. Trisomies are named based on which chromosome has the extra copy, so a person with trisomy 21 has an extra copy of chromosome 21. Trisomies are not typically inherited, and while women of any age can have a child with a trisomy, the likelihood increases with mother's age.1 People with trisomies are not all the same, but the common trisomies are associated with birth defects, intellectual disability and a range of health problems.