Down Syndrome

Down syndrome is a common type of birth defect that affects a child's cognitive functioning and other development. Researchers have determined what causes Down syndrome. Typically, fetuses develop with two chromosomes in each of the 23 pairs of chromosomes present in the human body. For each set, one of the chromosomes comes from the mother and the other from the father. However, children with Down syndrome have three chromosomes for chromosome pair 21.

Why do Children with Down Syndrome Have Three Chromosome 21s?

Researchers have identified three ways in which a child can be born with an extra Chromosome 21. For approximately 90% of children with Down syndrome, an abnormal cell division occurs during the development of the egg or sperm that causes three copies of Chromosome 21 to be present in all of the baby's cells. This is known as Trisomy 21. Children may also suffer from Down syndrome if some of their cells develop with a third copy of Chromosome 21 and some develop with the typical two copies. This is known as Mosaic Down syndrome. Finally, children may be diagnosed with Down syndrome if part of Chromosome 21 attaches to another chromosome. This is known as Translocation Down syndrome and it is the rarest type of this condition.

At this time, it is unknown what causes the extra Chromosome 21 that results in Down syndrome.

Living with Down Syndrome

Like children born with other genetic conditions, birth defects, and birth injuries, the severity of Down syndrome effects vary widely. Many children experience mild to moderate cognitive issues, different facial features, and gross motor delays. Additionally, approximately half of children born with Down syndrome experience some kind of heart defect and they are more likely to develop leukemia, serious infections, dementia, sleep apnea, obesity, seizures and other complications.