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What Is Trisomy 21 And How Is It Inherited?

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What Is Trisomy 21 And How Is It Inherited?

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Trisomy 21 (more commonly referred to as Down Syndrome) is a genetic condition caused by an extra copy of chromosome 21; resulting in 3 chromosomes instead of the usual pair.

Trisomy 21 is usually not inherited from parents, as males with Trisomy 21 (except for a few miraculous cases) are considered to be infertile. The creation of a third copy of chromosome 21 occurs as a random event in the creation of reproductive cells in a parent. Specifically, the problem that causes the 3rd copy of chromosome 21 is call nondisjunction. Nondisjunction is "the failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes" (Gottlieb, et al., 2023).

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Symptoms and Life Expectancy of Trisomy 21.

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Symptoms and Life Expectancy of Trisomy 21.

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The Symptoms of Trisomy 21:

The most apparent symptoms of Trisomy 21 are the physical differences it causes in the face and body. As shown in the image above, there are a range of features that are symptoms of Trisomy 21 including most noticeably slanted upturned eyes and a flat nose bridge. In many cases, there are also apparent differences in the skeletal structure of the head.

Affects of Trisomy 21 include:

Heart Disease

Skeletal Deformities

Movement Problems

Spine Disorders

Epilepsy

Hearing Loss

Sleep and Feeding Disorders

Developmental Disabilities (most common)

Trisomy 21 is unique in that unlike other genetic disorders such as Huntington's Disease, the symptoms and affects it has on the afflicted can range from mild to severe. For example, some people with Trisomy 21 can lead relatively normal lives, while others require care their entire life.

Life expectancy:

People with Trisomy 21 can lead relatively long lives, with most individuals living into their 60's. However, it is not uncommon for people with Trisomy 21 who are healthy to live into their 80's.

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Here is a link to a video with an excellent description of Trisomy 21, its cause, testing, and treatment!

Link: https://www.youtube.com/watch?v=ze_6VWwLtOE

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Importance of Understanding Trisomy 21 And Its Prevalence in Society.

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Importance of Understanding Trisomy 21 And Its Prevalence in Society.

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Trisomy 21 is the most common chromosomal anomaly in humans, with more than "5,000 babies being born with Trisomy 21 each year" (Children's Hospital of Philadelphia, 2024) and with more than 350,000 cases in the U.S. alone. I almost guarantee that you, the reader, have met someone with Trisomy 21. The prevalence of this disease in humans is why understanding Trisomy 21 is of the utmost importance. Not just for preventing the disease in future generations, but as an aid to individuals who live with Trisomy 21 to help them lead as healthy and enjoyable lives as possible.

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Testing:

Since its identification in 1866, testing for Trisomy 21 has advanced significantly. The majority of testing for Trisomy 21 is now down prenatally (before birth). The most common prenatal test for Trisomy 21 is through amniocentesis, where "a needle is inserted through the mother’s abdominal wall into the amniotic sac and a small sample of amniotic fluid is drawn out and tested in a laboratory" (Children's Hospital of Philadelphia, 2023). Postnatal testing includes a physical examination of the child and a DNA test from saliva of the child. Because Trisomy 21 has a wide range of severity, if a child is diagnosed with the disorder, further tests will be run to determine said severity. These tests can include X-Rays, MRI's, CT scans, and EOS imaging.

Treatment:

There is no cure for Trisomy 21. However, "treatment is ordered when certain issues — such as heart problems, muscle weaknesses or spinal curvatures — occur and need to be treated" (Children's Hospital of Philadelphia, 2023). Treatment is different patient to patient and could involve "therapy, surgery, or additional support services" (Children's Hospital of Philadelphia, 2023).

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MOSAIC: A Study Currently Being Done To Help Those With Trisomy 21 Combat Sleep Apnea.

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MOSAIC: A Study Currently Being Done To Help Those With Trisomy 21 Combat Sleep Apnea.

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Sleep Apnea, a disorder that causes people to stop breathing or breath shallowly during rest, affects only 5-10% of the general population compared to 50% of children with Trisomy 21 and 80% of adults with Trisomy 21. MOSAIC is a sleep apnea study for children being done by The University of Arizona. The study utilizes two FDA approved drugs, atomoxetine and oxybutynin, to in an attempt to strengthen the muscles in the airways, which have been shown to be noticeably weaker in children with Trisomy 21.

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Gottlieb, S. F. (2023, August 14). Genetics, nondisjunction. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK482240/

Health Library. (2024, May 1). Down syndrome: Symptoms & causes. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/17818-down-syndrome

LuMind IDSC Foundation. (2022, October 19). Down syndrome sleep apnea. LuMind IDSC Foundation. https://lumindidsc.org/down-syndrome-sleep-apnea

Philadelphia, T. C. H. of. (2023, March 1). Trisomy 21 (Down Syndrome). Children’s Hospital of Philadelphia. https://www.chop.edu/conditions-diseases/trisomy-21-down-syndrome#:~:text=Also%20known%20as%20Down%20syndrome,instead%20of%20the%20usual%20pair.