Incidence of mongolism and its diagnosis in the newborn.

An accurate estimate of the incidence in the general population of mongolism at birth is required for the genetic study of the disease. Penrose (1949) has estimated the frequency of the condition among children of school age in Great Britain from the records of local authorities; the incidence among children aged 10 to 14 is probably about 1 in 2,000. He stresses, however, that the high infant mortality of mongols implies that the incidence at birth is considerably higher than this. The only figure available for the incidence at birth in Great Britain is that given by Malpas (1937) for a maternity hospital; he found eighteen cases in 13,964 births, that is 1 in 776; but with such small numbers the random error may be large and mothers who have their babies in hospital are to some extent selected. For the U.S.A., too, the only figures available are based on the experience of single maternity units (Jenkins, 1933; Parker, 1950). The only factor known to be related to the incidence of mongolism is the mother's age, the apparent relation between birth order and mongolism being due to the association of maternal age and birth order (Penrose, 1933). So that while it is difficult to get any direct estimate of the incidence of mongolism at birth in the general population, it is probably correct to apply figures obtained from hospital births provided that due correction is made for the fact that mothers in hospital are rather younger than mothers having their confinements at home.