The obsolete medical terms Mongolian idiocy and Mongolism referred to a specific type of mental deficiency, associated with the genetic disorder now known as Down syndrome.
John Langdon Down first characterized what is now known as Down syndrome as a distinguishable form of mental disability in 1862, and in a more widely published report in 1866.
[5][6][7] Due to his perception that these children shared facial similarities with the populations that German physician Johann Friedrich Blumenbach described as the "Mongolian race", Down used the term "mongoloid" in his characterisation of these patients.
F. G. Crookshank published a pseudoscientific book in 1924 named The Mongol in our Midst which suggested that the syndrome was due to genetic traits literally inherited from Mongoloid races.
In 1961, genetic experts wrote a joint letter to the medical journal The Lancet which read: It has long been recognised that the terms Mongolian Idiocy, Mongolism, Mongoloid, etc.