Trisomy 21, also known as down-syndrome, is a genetic disorder in which a third copy of chromosome 21 is present. The disorder involves physical growth delays as well as distinct facial features. Young adults with down-syndrome have an average IQ of 50, and intellectual disabilities can range from mild to moderate. Although the parents of the child with down-syndrome are genetically normal, the child’s extra copy of chromosome 21 is due to chance. The probability in which a child may develop down-syndrome increases with increasing age of the mother. According to Journal of Genetic Counseling, “…since about the year 2000, women aged 35 and older have accounted for slightly more than 50% of pregnancies with Down syndrome” (Berkowitz, Roberts, Minkoff). The probability that a 20 year old mother would test positive in a prenatal screening is 0.1%, while for a 45 year old mother, that percentage is 3%. Due to access to termination of pregnancy and abortion, many parents will use a positive prenatal screening to justify pregnancy termination.
Down syndrome is the most common disease involving chromosomal abnormality in humans. 0.1% of babies born each year are diagnosed with down-syndrome. In 2013, globally, 8.5 million individuals suffered from down-syndrome, and 36,000 deaths resulted. That number is an improvement from the 43,000 deaths resulting from down-syndrome in 1990. Down-syndrome is named after John Langdon Down, a British doctor who discovered the chromosome abnormality in 1866. In 1959, French scientist Jérôme Lejeune discovered the extra copy of chromosome 21 present in those suffering from down-syndrome.
Trisomy 21 is caused by nondisjunction of chromosome 21 to separate during the development of gametes. Nondisjunction is more common in the female egg, with 88%, than in male sperm, 8%. During merging of the egg and sperm, that percentage is 3%. Trisomy 21 is the most common mechanism in the development of down-syndrome. However, Robertsonian translocation occurs in 2-4% of down-syndrome cases. Robertsonian translocation occurs when the longer arm of chromosome 21 attaches itself to another chromosome, which is often chromosome 14. This mutation may be present in the parents, or t may be a new mutation. If the mother is affected by the genetic condition, there is a 15% chance of having a child with down-syndrome. However, an affected father has a less than 5% chance of having a child with down-syndrome. This type of mutation is not affected by the age of the mother, like with Trisomy 21.
As of today, there is no cure for down-syndrome. Although education and a safe environment have been shown to improve the quality of life in patients of down-syndrome, many require specialized education and do not participate in the workforce. In the United States, only 20% of patients with down-syndrome participate in employment. Welfare opportunities and financial and legal support are often provided by the government or shelters. Due to access to specialized health care and social programs, life expectancy is between 50 and 60 years old for patients of down-syndrome. In 1960, sufferers of down-syndrome had an average life expectancy of 10 years old (CDC). Thanks to developments in medicine and biological study, those with down-syndrome are able to live longer and have a better quality of life. With continued social welfare programs and medical advancements, the quality of life for those with down-syndrome will continue to grow, until a cure is finally found to prevent the nondisjunction of chromosomes.
- “Data and Statistics.” Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 21 Oct. 2014. Web. 02 Dec. 2016.
- National Institutes of Health. U.S. Department of Health and Human Services, n.d. Web. 02 Dec. 2016.
- Challenging the Strategy of Maternal Age–Based Prenatal Genetic Counseling, Richard L. Berkowitz, MD Jaclyn Roberts, MD Howard Minkoff, MD