DISCREPANCY IN MOSAIC FINDINGS BETWEEN CHORIONIC VILLI AND AMNIOCYTES- A DIAGNOSTIC DILEMMA INVOLVING 45,X, 46,XY, AND 47,XYY CELL-LINES

Discrepancies between cytogenetic findings in chorionic villi (CV) and fetal tissue have been reported. Several embryogenic models have been proposed to explain such discrepancies. We describe a case in which a nalysis of the direct preparation showed 24% 45,X and 76% 46,XY, with 43% 45,X and 57% 46,XY cells in cultured villi. Amniocentesis results disclosed 97% 46,XY and 3% 47,XYY. No 45,X cells were found in culture d amniocytes. These findings suggest that nondisjunction occurred earl y in postzygotic cleavage resulting in 3 cell lines. It is postulated that through selection, the less viable 45,X cells died out among thos e destined to become fetus proper but persisted among the cytotrophobl ast and extraembryonic mesoderm cells. While there is probably selecti on against all aneuploid cell lines, 47,XYY cells are more likely to s urvive in the fetus. An explanation for the lack of 47,XYY cells in th e CV might be simply that the tissue sampled was not representative of the cytogenetic make up of the entire placenta.