From https://www.worlddownsyndromeday.org/about-wdsd
What is World Down Syndrome Day?
World Down Syndrome Day (WDSD) , 21 March, is a global awareness day which has been officially observed by the United Nations since 2012.
The date for WDSD being the 21st day of the 3rd month, was selected to signify the uniqueness of the triplication (trisomy) of the 21st chromosome which causes Down syndrome.
English 
Spanish