The epidemiology of Down Syndrome


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  1. Scenario of Family with Down Syndrome

My name is Joanne Johnson, and my 25 year old son has Down syndrome. When he was born the doctor suspected Down syndrome because of his distinct physical characteristics that suggested so, and with a tissue sample, the doctor confirmed that he had Down syndrome. At birth he was average sized, but as time wore on his peers outgrew him, and he appeared to be much smaller and different physically. Due to low muscle tone, he experienced many digestive issues, and raising him proved to be a challenge from the very start. As he grew older I explained to him that his physical appearance didn’t define him, and that it made him special, but as he grew older I learned I could no longer protect him from the harsh judgment of others. In elementary school his peers began to tease his flat face, and small broad nose and they excluded him from friend groups. Because of his poor muscle tone, he was never the star athlete in team sports like soccer or basketball, and soon learning became an evident challenge. He required special attention in order to grasp concepts in school, but at his own pace he was able to learn the main concepts just like the other kids. As he grew his passion became acting. He is now 25 years old and participates in many plays. Despite his success in acting he still is subject to much criticism and judgment on a daily basis. Finding a job is difficult, but during his spare time he works at the local convenience store at the checkout counter and he volunteers at events with other kids with Down syndrome to let them know that they aren’t alone. He proved to be a blessing in my life, and he brings me much joy. I couldn’t be more proud of him.

  1. Background Information

John Langdon Down, an English physician and doctor was the first to identify the syndrome as well as publish an accurate description of a person with Down syndrome in 1866. This earned Down the recognition as the “father” of the syndrome. Although others had previously recognized the characteristics, Down described the conditions distinctly. In 1959, the French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome. It was later determined that an extra partial or whole copy of chromosome 21 results in the characteristics associated with Down syndrome. [1] In the year 2000, an international team of scientists successfully identified and catalogued each of the approximately 329 genes on chromosome 21.[2] This accomplishment opened the door to great advances in Down syndrome research.

There have been many famous people with Down Syndrome, including Stephanie Ginnsz (The first actor with Down syndrome to play a leading part of the motion picture, Duo ), Lauren Potter (An American actress, who is known for her role as Becky Jackson on the television show Glee), Dr. Karen Gaffney (“The first living person with Down syndrome to receive aDoctor of Humane Lettersdegree for her long-standing humanitarian work in raising awareness about the capabilities of people who have Down syndrome through her roles as an accomplished sports figure, public speaker, and advocate”), Chris Burke (“An American actor, folk singer, and motivational speaker [, also] known for his character Charles "Corky" Thacher on the television seriesLife Goes On” , and many more.[3] While Down syndrome may burden one with physical limitations and obstacles, it surely does not completely suppress one’s ability to pursue passions and goals.

Physical manifestation, also known as the outward symptoms may include distinct facial features such a flat face, a small broad nose, abnormally shaped ears, a large tongue and upward slanting eyes with small folds of skin. Other physical features may include decreased or poor muscle tone, small head, ears, mouth, wide short hands and short fingers, and a short neck. [4]

According to the Centers for Disease Control (CDC), the 2011 estimated prevalence of Down Syndrome increased to 1/691 births. [This is a large increase from the 1/1087 in the 1990’s].[5] Male prevalence is (10.8), and higher in comparison to Female adolescents.[6] “Prevalence of DS by age group was the highest in 0-3 year olds at 11.1, declining to 10.3 among 4-7 year olds, 9.8 among 8-11 year olds, 8.3 among 12-15 year olds, and 6.0 among 16-19 year olds”. An increased risk for Down syndrome may be seen in relationship to a mother’s age. 80% of the Down Syndrome cases that occur are in mothers under 35 in the United States, however this is correlation may simply be because younger women have more children than older women. Generally, the risk of having a child with Down Syndrome is greatly increased with a mother’s age, particularly in ages 40 and over. When a mother conceives the first child with translocation Down Syndrome, having another child with Down Syndrome is greatly increased. [7]

Chart: Down Syndrome at Birth per 10,000 Live Births, 1979--2003. 1979-1983: 9.5; 1984-1988: 10.3; 1989-1993: 10.8; 1994-1998: 11.0; 1999-2003: 11.8.


  1. Scientific Information

Down syndrome is a developmental disorder caused by an extra copy of chromosome 21, therefore, Down syndrome is typically caused by nondisjunction. Nondisjunction is the failure of one or more pairs of homologous chromosomes to separate during the process of meiosis [egg (or sperm) formation]. When the egg joins a normal sperm to form an embryo, three chromosomes are made instead of the usual two. This extra chromosome is then copied over and over again and as a result, every cell in the babies’ body will have the extra chromosome copy. Because of this extra copy, individuals will have Down Syndrome because they have three copies of each gene instead of two. The extra chromosome copy makes it difficult for cells to properly function in the regulation protein production. Resultantly there will be an unideal production of protein has large consequences and because Down syndrome is caused by the presence of a whole chromosome, there is no specific location on the chromosome that Down syndrome is linked to.[9]

Nondisjunction is the cause for Down syndrome, and affects about 1/169 births. Male prevalence is relatively higher, and women who are conceiving their baby after the age of 40 have an increased chance of having a child with Down syndrome. Down syndrome has no strong relation to race, nationality, actions of mother or father during pregnancy, etc. After the age of 40, the risk is increased with mother’s age, however if the first child has translocation Down Syndrome, having another child with Down syndrome is greatly increased. [10]


Risk of having a baby with Down syndrome

25 years

1 in 1,250

30 years

1 in 1,000

35 years

1 in 400

40 years

1 in 100

45 years

1 in 30








Possible Nondisjunction Pedigree

In the body, it is suggested that “The cognitive and developmental problems associated with Down syndrome are linked to a key brainprotein. This protein is SNX27 which is needed by the brain in order for neurons to function properly”. [11] Down syndrome people’s brains have lower levels of the protein SNX27, however SNX27 is imperative for brain function since it keeps glutamate receptors on the surface, allowing neurons to work. The extra chromosome 21 that encodes a micro MRNA (miR-155), and the extra miR-155 allow SNX27 levels to drop, decreasing glutamate receptors. Because people with Down syndrome have significantly lower levels of SNX27 a strong correlation can be seen between the low levels of SNX27 and increase of MiR-155. It has been concluded that the lack of SNX27 protein suppresses one’s brain function and ability to learn, retain memory, and behave.[12] Unfortunately, there currently are no treatments available to relieve this issue.

  1. Resources for Patients and their Families

National Resources

  1. National Down’s Syndrome Society’s Hotline


  1. National Down Syndrome congress

  1. Global Down Syndrome Foundation

Local Resources

  1. Puget Sound and Western Washington Down Syndrome Community

[1]1. National Down Syndrome Society - The National Advocate for People with Down Syndrome Since 1979. "What Is Down Syndrome? - National Down Syndrome Society." Accessed January31,2014.

[2]2. American Pregnancy Association. "Down Syndrome: Trisomy 21." Accessed January31,2014.

[3]3. Wikipedia, the free encyclopedia. "Down syndrome." Accessed January31,2014.

[4]4. NICHD - The Eunice Kennedy Shriver National Institute of Child Health and Human Development Official Home Page. "What are common symptoms of Down syndrome?" Accessed January31,2014.

[5]5. Centers for Disease Control and Prevention. "CDC Data & Statistics | Feature: Down Syndrome Cases at Birth Increased." Accessed January31,2014.

[6]6. Centers for Disease Control and Prevention. "CDC Data & Statistics | Feature: Down Syndrome Cases at Birth Increased." Accessed January31,2014.

[7]7. NICHD - The Eunice Kennedy Shriver National Institute of Child Health and Human Development Official Home Page. "What are common symptoms of Down syndrome?" Accessed January31,2014.


[9] National Down Syndrome Society - The National Advocate for People with Down Syndrome Since 1979. "What Is Down Syndrome? - National Down Syndrome Society." Accessed January31,2014.

[10]9. Global Down Syndrome Foundation. "Down Syndrome Research and Medical Care Timeline." Accessed January31,2014.

[11]10. The Huffington Post. "Brain Protein Linked To Down Syndrome May Be Cause Of Learning & Memory Problems." Accessed January31,2014.

[12]11. Beaker — Sanford-Burnham Science Blog. "Unraveling the molecular roots of Down syndrome." Accessed January31,2014.

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