Phenotypic spectrum of 45,X/46,XY individuals.

We report on five patients with 45,X/46,XY mosaicism. In these subjects, as well as in 58 individuals from the literature with a similar chromosome constitution, we did not find a preponderance of 46,XY cells among patients showing ambiguous to abnormal male external genitalia when compared to those patients with slight or no virilization. However, the average frequency of 46,XY cells in blood in these mosaic individuals suggests that this sample includes mainly individuals whose mosaicism originated early in embryonic cell division. Those individuals whose mosaicism originated later are not significantly represented in this sample and would have higher frequencies of 46,XY cells. These individuals would be excluded from an intersex sample if they had well-virilized genitalia. This ascertainment bias suggests that the degree of virilization depends on the frequency of 46,XY cells.