World Down Syndrome Day is celebrated on March 21 for those with Down syndrome. It is a celebration and a day for worldwide awareness that started in 2012. It is celebrated on March 21 because of the twenty first chromosome trisomy, which is the cause for Down syndrome. On Dec. 19, 2011 the United Nation General assembly officially declared March 21 to be the day of World Down Syndrome Day and all are invited to celebrate and support the people with Down syndrome.