Acrocentric chromosome polymorphisms: beware of cryptic translocations.

Cryptic translocations may escape diagnosis, especially when they implicate chromosomal regions that are known to be polymorphic in the human karyotype. We describe a case of postnatal diagnosis of Beckwith-Wiedemann syndrome (BWS) due to an unbalanced translocation that had not been diagnosed in the fetal karyotype. This first cytogenetic analysis revealed that one chromosome 14 presented as a common acrocentric short arm polymorphism. Further analyses after birth, using C-banding, NOR staining and fluorescence in situ hybridization (FISH) with telomeric probes, revealed that it was the result of an unbalanced de novo t(11;14)(p15;p13) translocation leading to partial 11p trisomy and to BWS. Prenatal cytogenetic management of such apparently inoffensive chromosome markers is discussed.