Recent endeavors to throw light on the etiology of Mongolian idiocy have resulted in considerable literature on the subject during the past few years. The rarity of its occurrence in more than one child in a family is an observation of universal note.
Goddard1 has collected the histories of 322 cases of Mongolian idiocy, and in not one instance was there a history of more than one Mongolian child in the family. McClelland2 remarks that it is a common observation that in no family was more than one Mongolian idiot encountered. Shuttleworth3 says that the production of more than one Mongol in the same family is a great rarity, he himself having heard of only two cases and having never seen any. He also reports the case of twins, one normal and the other a Mongol, as does Swanberg.4 Dr. Max Schlapp, in the course of
PARDEE IH. TWO CASES OF MONGOLIAN IDIOCY IN THE SAME FAMILY. JAMA. 1920;74(2):94-95. doi:10.1001/jama.1920.02620020026013