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What is Down syndrome? | Live Science

Down syndrome is a condition in which a person has a fully or partially duplicated copy of chromosome 21. (A chromosome is a structure made up of DNA and proteins found in the nucleus of each cell.) Typically, each person has 23 pairs, or 46 total chromosomes. In a person with Down syndrome, there are three copies of chromosome 21 instead of two. This duplication produces a number of effects, including cognitive differences, distinctive facial features and an increased risk of certain health conditions, such as heart problems. The causes of many of these effects are not totally understood.

The condition is named for John Langdon Down, a British doctor who is considered the first to fully describe the condition as a distinct group of characteristics, in 1862, according to the National Down Syndrome Society. Others had described elements of the condition earlier, and descriptions of people who likely had Down syndrome go back much further. In 1959, French doctors Jérôme Lejeune and Marthe Gautier linked the condition with the extra copy of chromosome 21 for the first time.

What is Down syndrome? | Live Science Source link What is Down syndrome? | Live Science

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