📖 what
What is Down syndrome?
Human BiologyGenetic Disorders
Quick Answer
Down syndrome is a genetic condition caused by an extra copy of chromosome 21. It is also called trisomy 21.
The Full Story
Down syndrome is the most common chromosomal condition associated with intellectual disability. It usually results from trisomy 21, meaning a person has three copies of chromosome 21 instead of two. The condition was first described medically by John Langdon Down in 1866, and the chromosome cause was identified later in 1959. People with Down syndrome may have characteristic physical features and a range of health and developmental differences.
Key Facts
1.It is usually caused by trisomy 21
2.John Langdon Down described the syndrome in 1866
3.The chromosome basis was identified in 1959
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"The chromosome condition caused by an extra 21"