Jumping Translocation at Prenatal Diagnosis
Jumping translocations are defined as translocations involving one donor chromosome and numerous recipient chromosomes. They are rarely seen as constitutional abnormalities and even less likely to be detected at prenatal diagnosis. We describe a case of a jumping translocation, detected at CVS, involving the pericentromeric region of chromosome 18. Follow up amniocentesis and analysis of fetal tissue from the products of conception both indicated stability of a deleted 18p cell lineage. In contrast multiple cell lines, all involving a breakpoint in the pericentromeric region of chromosome 18, were detected at CVS (villi) and at multiple sites of the placenta. These results indicate that cells prior to chorion and fetal cell differentiation were most likely to have been deleted for 18p. The chorionic mesoderm cell lineage then underwent multiple translocations and rearrangements to become mosaic, while the amniotic ectoderm and fetal cells solely retained the unbalanced deleted 18p. This case provides new insight into constitutional jumping translocations in that the contrasting results between placenta and fetus may indicate that these translocations are tissue limited or confined to specific cell lineages during embryogenesis. This has genetic counselling implications for prenatally detected jumping translocations, especially when detected at CVS.