What is the difference between down syndrome and mongoloid?

None. "Mongoloid" is: considered an ethnically pejorative term & is no longer used to describe the facial features of flat mid-face, flat nasal bridge, epicanthic folds, skin folds of the inner corners of the eyes & up-slanting palpebral fissures or eye openings that are characteristic facial features of people with Down Syndrome but also are seen in many perfectly neurotypical individuals of Asian descent.

Knowledge: Before we were aware of the chromosome defect in Down syndrome there were many suggestions about origin.After Darwin, there an attempt to link it as a missing link and to the Mongolian race because of some physical features.Such terminology is still found in books written in the late 19th and early 20th century, but as knowledge has enlightened us, its use has disappeared.