Risk of dual occurrence of mongolism in sibships.

A survey of sibships containing a mongol was undertaken to determine the risk to the mother of bearing a second mongol. Opposing views have been expressed on the subject of familial incidence of mongolism. Benda (1947), Engler (1949) and 0ster (1953a, 1956) have all stated or implied that the risk of bearing a second mongol child is no greater than the general risk of having a mongol. On the other hand, Penrose (1933) regarded the incidence of more than one mongol in a fraternity as greater than the random expectation. Book and Reed (1950) stated that a woman who had borne a mongol had a 20 to 60 times greater chance of having another child similarly affected than if no mongol had been born in her family. Oliver (1950) concluded that the risk of a mother of a mongol having a second one was about 40 times that of any mother producing a child with mongolism. Carter, Hamerton, Polani, Gunalp and Weller (1960) referred to the experience at The Hospital for Sick Children, London, which has shown that 'the risk of parents having a second mongol child is almost certainly raised above the random risk, especially at the younger maternal ages'. Despite these diverging views, there is a striking absence of reported extensive studies. This may be because such studies should be on a scale large enough to provide a substantial number of children born subsequent to a mongol. In the first place, because of the well-established tendency for mongols to be born to relatively old mothers, the likelihood of further children is reduced. Second, the fact of having had a mongol child may act as a deterrent to further child-bearing. Though no larger series on the incidence of mongolism among siblings born after a mongol appears to be available (the only comparably-sized series we were able to find was that of 0ster (1956), which contained 343 siblings born after a mongol, among whom there were four further instances of mongolism), we realize that our numbers are not great. We record our findings, however, with the hope that similar data will be collected from other sources, and that sufficient will become available to substantiate or modify our tentative conclusions.