Down's syndrome vs mongolianism

Down's syndrome and mongolianism both are nouns.

Word	Noun	Adjective	Verb	Adverb
Down's syndrome	Yes	No	No	No
mongolianism	Yes	No	No	No

As nouns, Down's syndrome and mongolianism are synonyms defined as:

Down's syndrome and mongolianism: a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation

Other synonyms of Down's syndrome include Down syndrome, mongolism, trisomy 21.

Down's syndrome (noun)	mongolianism (noun)
a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation	a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation