What is Down Syndrome?

Down syndrome or Down's syndrome, is a congenital condition that usually causes some degree of learning disability and is typically characterized by certain physical features. In the UK, approximately 750 babies are born with Down syndrome every year and the condition affects individuals of all ethnicities.


Some examples of the typical features seen in people born with Down syndrome include:

  • Reduced muscle tone or hypotonia
  • Eyes that slant upwards and a flat nasal bridge
  • A single crease across the palm known as the palmar crease
  • Low birth weight
  • Delayed ability to crawl and walk
  • Some degree of learning disability

Although many individuals with Down syndrome share characteristic features of the condition, they look different to each other and usually resemble their mother, father or other family members.

The level of learning disability also varies between individuals, with some only experiencing mild intellectual disability (IQ 50 to 70) and others experiencing severe difficulties (IQ 20 to 35).


Down syndrome is caused by the presence of an additional copy of chromosome 21 in a person’s cells. This extra copy is acquired by chance and although Down syndrome is more common among babies born to mothers of an older age, mothers of any age may have a baby with the condition.

Humans usually have 46 chromosomes in every cell, with 23 inherited from each parent. Due to the extra copy of chromosome 21, people with Down syndrome have 47 chromosomes in their cells. This additional DNA causes the physical characteristics and developmental problems associated with the syndrome.


Down syndrome is an incurable condition but there are many children with this condition who grow up to lead fulfilling lives. Down syndrome can be identified before birth using antenatal screening and further tests to confirm the likelihood of a child being born with the condition. To detect the likelihood of Down syndrome, the number and appearance of chromosomes present in the nucleus are assessed using a process called karyotyping.

Further Reading

Last Updated: Feb 26, 2019

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2019, February 26). What is Down Syndrome?. News-Medical. Retrieved on December 07, 2022 from https://www.news-medical.net/health/What-is-Down-Syndrome.aspx.

  • MLA

    Mandal, Ananya. "What is Down Syndrome?". News-Medical. 07 December 2022. <https://www.news-medical.net/health/What-is-Down-Syndrome.aspx>.

  • Chicago

    Mandal, Ananya. "What is Down Syndrome?". News-Medical. https://www.news-medical.net/health/What-is-Down-Syndrome.aspx. (accessed December 07, 2022).

  • Harvard

    Mandal, Ananya. 2019. What is Down Syndrome?. News-Medical, viewed 07 December 2022, https://www.news-medical.net/health/What-is-Down-Syndrome.aspx.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment
You might also like...
What parents need to know about prenatal tests | BGI Perspectives