MONGOLISM is a congenital anomaly of unknown etiology. Attempts to attribute it to any single cause or to a combination of etiologic factors have failed. One main reason is that no experimental approach to the subject has been possible because the condition is recognized only in man. As a rule, mongolism occurs sporadically in family pedigrees, as well as among siblings; this circumstance indicates that the factor, or the combination of factors, which leads to this entity occurs only rarely. Therefore, cases of repeated incidence in a family have always aroused great interest and have been looked on as experiments of nature of possible value in contributing to an eventual understanding of mongolism.
Up to the present, forty-eight families have been reported in which mongolism occurred more than once among siblings. The data are exclusive of those pertaining to families in which there were 2 mongoloid children who constituted a