The relative aetiological importance of birth order and maternal age in mongolism

Mongolian imbeciles are very often born last in a long family. The fact, which was pointed out many years ago by Shuttleworth (1909), has led clinicians to believe that mongolism is to believe that mongolism is to some extent a product of the exhaustion of maternal reproductive powers due to frequent child-bearing (Still, 1927; Fantham, 1925). The conclusion is widely accepted with the reservation that the affected child is not necessarily born at the end of the family (Thompson, 1925). Several cases are first-born, in fact, and it is sometimes stated that the condition occurs more frequently in first and last children than in other ordinal positions. There is, however, ample evidence that mongolian imbeciles have a significantly later birth rank than normal children (Hogben, 1931). It is also established, from large numbers of figures which have been collected, that the maternal age at the birth of mongolian imbeciles is unduly high. Though some of these imbeciles have young mothers, most of the cases (about 70%) are born after the mother has reached the age of 35 years. Thus the maternal age itself is likely to be an aetiological factor quite as important as birth order. I Know of no serious attempt, however, to distinguish between the aetiological significance of these two factors: to do this is the task I have umdertaken.