Down syndrome (or Trisomy 21) is a condition in which a person has an extra chromosome. Chromosomes are "packages" of genes in the body. They determine how a
baby's body forms and functions as it grows.

Around 1 in every 800 babies will be born with Down syndrome.

Down syndrome occurs naturally – there is no known cause.

Down syndrome usually causes varying degrees of intellectual and physical disability and associated medical issues.

The day is celebrated in an effort to raise awareness about Down syndrome and to advocate for the rights, inclusion, and well-being of people with Down syndrome. 

The date was selected because Down syndrome is caused by the presence of a third copy of the 21st chromosome, and 21/3 (March 21st) represents this genetic condition.

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