Presumptive mosaic origin of an XX/XY female with ambiguous genitalia

A child with ambiguous genitalia had an Xx/XY karyotype in ali tissues examined. Analyses of Il informative polymorphisms. both chromosomal andgenetic (Rh and HLA). showcd no difference between thc two celi lines. Il is unlikely that the child originated from fertilisation of the egg and the second polar body by two sperms: therefore. we hypothesise thal the child originated from an XXY zygote after milotic errors during cleavage. Recent findings of differences in the chromosome constitution between the extraembryonic tissues and the fetus suppon this view.