Is the most common trisomy at the time of birth. Also called Down syndrome, it is associated with moderate to severe intellectual disabilities and may also lead to digestive disease, congenital heart defects and other malformations.

Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome) are associated with a high rate of miscarriage. These babies are born with severe brain abnormalities and often have congenital heart defects as well as other birth defects. Most affected individuals die before or soon after birth, and very few survive beyond the first year of life.

Also called Turner Syndrome or 45, X. This is caused by a missing copy of the X chromosome. Girls with Monosomy X may have heart defects, hearing problems, minor learning disabilities and are usually shorter than average. As adults they are often infertile.

Also called 47, XXY. This is caused by an extra copy of the X chromosome in boys. Boys with Klinefelter syndrome may have learning disabilities, tend to be taller than average, and most men with this condition are infertile.

Also known as 47, XXX. This is caused by an extra copy of the X chromosome in girls. Some girls with triple X syndrome have learning disabilities, and most are taller than average.

Also called Jacob’s syndrome or 47, XYY. This is caused by an extra copy of the Y chromosome, and only affects boys. Boys with this condition tend to be taller than average and may have associated mild learning and behavioral difficulties.