Risk of Dual Occurrence of Mongolism in Sibships

Abstract

The risk of another mongol being born to a mother who had already had such a child was investigated. Records from London and Surrey of 778 sibships containing a mongol were studied, the propositi consisting both of subjects living at home and those in institutions. Two hundred and thirty-five mothers of 778 mongols (30%) had known subsequent live-births, a total of 367 in all, among whom were seven second cases of mongolism (one in 52). Analysis of the 367 subsequent births, in relation to maternal age, showed a 3.7 times greater incidence of mongolism than the incidence expected if there has been no increased risk of having a second mongol. This increased incidence is statistically significant. It is tentatively concluded that the general risk of having another mongol is increased nearly four-fold once a mother has had such a child. If similar data were collected from other sources, this conclusion could be substantiated or modified, and sufficient information would become available to subdivide the general figure for the increased risk of bearing a second mongol into risk figures at various maternal ages. Nine of the 778 mongols were products of twin birth (one in 86) suggesting, on the basis of an incidence of mongolism of one in 666 maternities, an association of twinning with mongolism, in this country, one in about 57,000 births. Of the nine twin pairs, one was concordant for mongolism (a same-sex pair) and the other right discordant (both same- and opposite-sex pairs).