Reciprocal translocations: a trap for cytogenetists?
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We report four cases of subjects with phenotypic abnormalities and mental retardation associated with apparently balanced translocations, two inherited and two de novo, which showed, by molecular analysis, a hidden complexity. All the cases have been analyzed with different molecular techniques, including array-CGH, and in two of them the translocation breakpoints have been defined at the level of base pairs via studies in somatic hybrids containing single derivative chromosomes. We demonstrated that all the translocations were in fact complex rearrangements and that an imbalance was present in three of them, thus accounting for the phenotypic abnormalities. In one case, a Prader–Willi subject, we were not able to determine the molecular cause of his phenotype. This study, while confirming previous data showing unexpected complexity in translocations, further underscores the need for molecular investigations before taking for granted an apparently simple cytogenetic interpretation.
KeywordsReciprocal Translocation Pericentric Inversion Balance Translocation Painting Probe Translocation Breakpoint
We are grateful to the YAC Screening Centre of San Raffaele Biomedical Science Park (Milan) for providing BAC clones. This work was supported by cofin02- and cofin03-MIUR (to O.Z.), cofin04-MIUR (to E.R.), the FIRB 2001 (to O.Z.), the Italian Telethon Foundation (GP0247Y01 to O.Z.) and the Cariplo Foundation (to E.R. and O.Z.).
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