Discrepancies in cytogenetic results between different tissues in two fetuses with Wolf- Hirschhorn syndrome.

Discrepant unbalanced structural chromosome aberrations between placental and fetal tissue, both involving the short arm of chromosome 4, were found in two human fetuses affected with Wolf-Hirschhorn syndrome. In the first instance, placental chromosome examination revealed a del(4) (p14), whereas fetal fibroblast chromosomes showed an unbalanced der(4)t(4;13)(p14;q11) translocation. In the second instance, placental karyotyping revealed a 4p+ chromosome, while amniocytes showed a submicroscopic deletion at 4p16.3. Since confirmation of structural aberrations from placental tissue is mostly not sought if the phenotype of the fetus is abnor- mal, discrepancies between karyotypes obtained from placental tissue and amniocytes or fetal tissues might be more frequent than the rare reports published so far would suggest. It is unclear whether the simple deletion or the more complex rearrangement is the primary aberration from which the other derived. Structural chromosome aberrations often have a much more complex mechanism of formation than the end product would suggest, and secondary rearrangements of a given aberration in the zygote are more frequent than expected.