Trisomy 21 is a congenital genetic disorder and it is not possible to generalize how long a patient can live. Trisomy 21, also known as Down syndrome, is caused by the failure to separate chromosome 21 during meiosis during germ cell formation, resulting in the formation of aneuploid abnormal gametes with abnormal chromosome numbers. Patients may have specific facial features such as a low nasal bridge, wide eye spacing, small eye fissures, internal canthus, large tongue extension, as well as growth retardation and short limbs. About 60% of the children may be aborted in the womb. Some of the surviving children may also die between 3 and 6 months of age. If they survive into adulthood, they often show signs of dementia. Therefore, prenatal diagnosis by cytogenetic methods through collection of chorionic villi or amniotic fluid is recommended to prevent the birth of children with trisomy 21 during pregnancy.