In general, it is obvious that the factor or factors that bear a direct causal relationship to a condition which is clearly apparent at the time of birth—as, according to Brousseau,1 is the case with mongolism—must operate at the time of the formation of the gametic chromosomes or subsequently, during the development of the embryo but before the time of delivery. It is believed that a knowledge of the exact time at which such factors operate would markedly facilitate progress toward an understanding of the etiology of such a condition.
If the condition is produced by genetic factors, then it should be possible to demonstrate among closely related persons who bear any given trait specific relationship configurations that would be diagnostically characteristic of such hereditary factors. The simplest and most definite of these are the various but well known forms of simple mendelian inheritance. But when clearcut
SOUTHWICK WE. TIME AND STAGE IN DEVELOPMENT AT WHICH FACTORS OPERATE TO PRODUCE MONGOLISM. Am J Dis Child. 1939;57(1):68–89. doi:10.1001/archpedi.1939.01990010077006
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