A possible explanation for the low incidence of gonosomal aneuploidy among the offspring of triplo-X individuals.

A review of the reproductive performance of 47,XXX individuals showed that the incidence of gonosomal aneuploidy among the offspring is low. To explain this unexpected phenomenon it is hypothesized that fertile triplo-X individuals have chromosomally normal oogonia due to mitotic nondisjunction in a cell from which the primordial germ line took origin. Mosaic 46,XX/47,XXX individuals have a somewhat higher risk of bearing aneuploid offspring, possibly due to a constitutional tendency toward gonosomal nondisjunction.