The Lessons of Polyploidy

Elsewhere in this issue (p 367), Pai et al report still another phenotypic manifestation of triploidy in man: increased RBC indices. This can be added to those already described in triploidy, such as increased size of other types of cells,1arborizing polyps of the amnion,2ocular colobomata, asymmetry, syndactyly of fingers and toes, and intrauterine growth retardation.3Most observations have been made on patients with diploid-triploid mosaicism, since the longest known survival in a case of pure triploidy is five months.4 Triploidy is a triplication of each chromosome, rather than the duplication seen in the normal diploid set. Thus, the sex chromosomes must be abnormally triplicated (69,XXX or 69,XXY), with the strong possibility of genital abnormalities in the male. That the entirely triploid babies are able to survive even a few months seems remarkable, considering the magnitude of the chromosome changes. Of course, most are never