Trisomy - Human Trisomy

Human Trisomy

Trisomies can occur with any chromosome, but often result in miscarriage. For example, Trisomy 16 is the most common trisomy in human pregnancies, occurring in more than 1% of pregnancies; only those where there are a number of cells with a normal complement of chromosomes called mosaic trisomy 16 survive. This condition, however, usually results in spontaneous miscarriage in the first trimester.

The most common types of autosomal trisomy that survive to birth in humans are:

• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Trisomy 9
• Trisomy 8 (Warkany syndrome 2)
• Trisomy 22

Of these, Trisomy 21 and Trisomy 18 are the most common. In rare cases, a fetus with Trisomy 13 can survive, giving rise to Patau syndrome. Autosomal trisomy can be associated with birth defects, mental retardation and shortened life expectancy.

Trisomy of sex chromosomes can also occur:

• XXX (Triple X syndrome)
• XXY (Klinefelter syndrome)
• XYY