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  2. Down syndrome - Symptoms and causes - Mayo Clinic

    www.mayoclinic.org/diseases-conditions/down-syndrome/symptoms-causes/syc-20355977

    Symptoms & causes. Diagnosis & treatment. Doctors & departments. Overview. The genetic basis of Down syndrome Enlarge image. Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.

  3. Down Syndrome: Symptoms & Causes - Cleveland Clinic

    my.clevelandclinic.org/health/diseases/17818

    Down syndrome is a genetic condition where a person is born with an extra copy of chromosome 21. This means that they have a total of 47 chromosomes instead of 46. This can affect how their brain and body develop. People diagnosed with Down syndrome have happy and healthy lives with supportive care.

  4. What causes Down syndrome? | NICHD - NICHD - Eunice Kennedy...

    www.nichd.nih.gov/health/topics/down/conditioninfo/causes

    Down syndrome is caused by a random error in cell division that results in the presence of an extra copy of chromosome 21. The type of error is called nondisjunction. Usually when one cell divides in two, pairs of chromosomes are split so that one of the pair goes to one cell and the other from the pair goes to the other cell.

  5. Down syndrome - Wikipedia

    en.wikipedia.org/wiki/Down_syndrome

    Down syndrome (also known by the karyotype 47,XX,+21 for females and 47,XY,+21 for males) [98] is mostly caused by a failure of the 21st chromosome to separate during egg or sperm development, known as nondisjunction. [91] As a result, a sperm or egg cell is produced with an extra copy of chromosome 21; this cell thus has 24 chromosomes.

  6. Down Syndrome: Causes, Types, and Symptoms - Healthline

    www.healthline.com/health/down-syndrome

    Down syndrome is the most common genetic condition in the United States. We’ll explain the causes, symptoms, and outlook of this condition.

  7. Down Syndrome: Causes and Risk Factors - Verywell Health

    www.verywellhealth.com/what-are-the-causes-of-down-syndrome-2633265

    Down syndrome (trisomy 21) is caused by a genetic anomaly in which there is an extra chromosome 21. Advanced maternal age is the only risk factor. Skip to content

  8. Down syndrome is usually 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.

  9. Down Syndrome | Birth Defects | CDC - Centers for Disease Control...

    www.cdc.gov/birth-defects/about/down-syndrome.html

    Down syndrome is a genetic condition where a person is born with an extra chromosome. This can affect how their brain and body develop. People diagnosed with Down syndrome can lead healthy lives with supportive care.

  10. Down Syndrome: Causes, Symptoms, Diagnosis, and Treatment - WebMD

    www.webmd.com/children/understanding-down-syndrome-basics

    People with Down syndrome have an extra chromosome that impacts their looks and their ability to think, learn, and reason. Discover the type, causes, and kinds of effects it can have.

  11. Trisomy 21 (Down Syndrome) - Children's Hospital of Philadelphia

    www.chop.edu/conditions-diseases/trisomy-21-down-syndrome

    Causes. Down syndrome occurs because of the extra copy of chromosome 21, which can cause the body and brain to develop differently than a child without the syndrome.