Genetic Studies and Chromosomal Analyses in Families with Mongolism (Down’s Syndrome) in more than one Member

Abstract

The pedigrees of 6 pairs of sibs and 17 other families where Down''s syndrome has occurred more than once are presented. Parental age data were collected in all families and chromosomal analyses performed on almost all the living mongols and a number of normal parents and sibs. Chromosomal translocation was not the underlying cause of the multiple occurrence of mongolism in any of the 21 families where chromosomal analysis was successful on at least one of the patients with Dawn''s syndrome. In every family either the proband or his relative or both were found to have the regular trisomic karyotype. Translocation mongols occurred in 4 families (2 of the 13-15/21 (D/G) and 2 of the 21-22/21 (G/G) type); in each family the other mongoloid relative was of the regular trisomic type. Mean maternal ages were computed separately in families where the genetic connection between the mongol relatives was through the mother and through the father. The former value was compared with mean maternal ages of all mongols in 3 institutions for the retarded. An approximate estimate of the significance of the maximum difference between the means placed it on the borderline at the 5% level of probability.