Rock Your Socks World Down Syndrome Day Shirt. Show you love someone special with this t-shirt. World Down Syndrome Day (WDSD) is on March 21st. Three #21 chromosomes or Trisomy 21 results in down syndrome, thus we observe World Down Syndrome day, 3/21. A cute groovy down syndrome socks t-shirt for anyone wanting to wear wear blue and yellow ribbons and designs to support down syndrome awareness. A cute T21 Tribe Shirt. Click our brand name for more styles. Lightweight, Classic fit, Double-needle sleeve and bottom hem