Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or parts of a third copy of chromosome 21. It is typically associated with physical growth delays, characteristic facial features, and lower mental ability.
Who are the parents?
Most parents of the affected children are usually genetically normal. The extra chromosome occurs by chance. It is more common among parents with a family history and older women, especially those above 35. Some researchers suggest that the age of men matters too since genetic mutations in their sperm increase rapidly with age. One study showed that children can inherit four times as many new mutations from their fathers than their mothers
How common is Down syndrome?
Globally, it occurs in about one per 1000 babies born. A woman who has already given birth to a baby with trisomy 21, is more likely to do so again. The possibility for an extra chromosome increases from less than 0.1% in 20-year-old mothers to 3% in those age 45.
How do children get Down syndrome?
Down syndrome is caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This type of down syndrome, which accounts for 95% of cases, is called trisomy 21. A less common type is called Mosaicism. It is diagnosed when there is a mixture of two types of cells.
Testing for Down syndrome during pregnancy
Pregnant women are screened for Down syndrome from week 10 of pregnancy. After birth, it can be diagnosed by examination and testing. If a screening turns out to be positive, some parents decide to terminate the pregnancy. Other parents decide to accept their baby as it is and later often report to have a wonderful life with their children.
- Mental impairment
- Stunted growth
- Umbilical hernia
- Narrow roof of the mouth
- Flat head and flat nose
- Abnormal outer ears
- Separation of first and second toes
- Hearing and vision disorders
- Heart problems
- Low IQ — the average IQ of a young adult with Down syndrome is 50, equivalent to the mental ability of an 8- or 9-year-old child
Cure and life
There is no known cure for down syndrome. However, due to advances in medical technology, individuals with Down syndrome are living better than ever. Education and proper care can improve quality of life. Some kids with Down syndrome graduate from high school and a few even can attend post-secondary education. Kids and adults with trisomy 21 are generally happy.
Individuals with Down syndrome are living longer than ever before as a result of advances in medical technology. In 1910, the life expectancy of children with Down syndrome was nine years. With the discovery of antibiotics, the average survival age has increased to 20. Now, with recent advancements in clinical treatment, most particularly corrective heart surgeries many adults with Down syndrome reach age 60, and some live even longer — often very happily.
- National Down Syndrome Society, NDSS (http://www.ndss.org/about-down-syndrome/down-syndrome/)
- Parental Influence on Human Germline De Novo Mutations in 1,548 Trios from Iceland, Nature (https://www.nature.com/articles/nature24018 )
- Screening Tests During Pregnancy, Mayo Clinic (https://www.mayoclinic.org/diseases-conditions/down-syndrome/diagnosis-treatment/drc-20355983)