A case of Mongolism in DZ female twins studied at 10 and then at 43 years of age.

A pair of female mongoloid twins was studied when they were ten years old and, again, some thirty years later. A careful comparison was made of the similarities and differences between them in features or traits which have proved to be useful in determining the zygosity of like-sexed twins. Though some of these characters can be, and frequently are, considerably modified in the presence of mongolism and so lose part of their value for that purpose, the differences noted in these twins, both as children and as middle-aged adults, are thought to outweigh their similarities and so warrant the conclusion that they are, indeed, dizygotic.