The chromosome abnormality in mongolism.

In an examination of our present knowledge regarding chromosome anomalies in mongolism the anomalies of trisomy-21 (the commonest anomaly in association with mongolism), 13-15/21 translocation and 21-22/21 translocation were illustrated and discussed. The relatively uncommon chromosome translocations and chromosome mosaicisms found in association with mongolism have especial clinical importance. Translocation of either type may occur as an isolated finding in a mongoloid patient. However, the translocation chromosome is frequently also found in one of the phenotypically normal parents. This is associated with an increased incidence of mongolism in the offspring, though the actual risk figure is uncertain in view of the small number of families described to date. The occurrence of chromosome mosaicism in mongolism may be associated with incomplete manifestation of the syndrome, and the ultimate mental development in such patients has varied from normal to severely retarded in cases described in the literature.