Directional genomic hybridization (dGH™) identifies small, inverted duplications in situ

Thomas Liehr^1,2*Erin Cross³Stefanie Kankel^1,2

• ¹Friedrich Schiller University Jena, Jena, Germany
• ²University Hospital Jena, Jena, Thuringia, Germany
• ³Kromatid, Inc, Longmont, United States

While fluorescence in situ hybridization (FISH) is a standard approach for characterizing the chromosomal structure involving a region of interest, FISH to target single chromatids is not routinely performed. However, this latter approach seems principally suited to distinguish small, tandem inverted duplications, from direct duplications in clinical cases. A commercially available single-chromatid-FISH approach called "directional genomic hybridization (dGH™) has been applied here in nine cases of small supernumerary marker chromosomes (sSMC) known to have inverted duplications. The successful detection of small, inverted duplications has been demonstrated here for the first time using a custom Kromatid dGH™ InSite assay. For all five of the euchromatic sSMCs, inversions were detected with the dGH single-chromatid molecular cytogenetic assay. Thus, the dGH method of FISH™ is a readily applicable, straightforward approach to identify small, inverted duplications undetectable by conventional (molecular) cytogenetic methods. It may be used to identify the presence of small inversions within regions presenting a copy number gain identified by chromosome microarray. Distinguishing small, inverted duplications from direct duplications, may have an impact on topologically associating domains and thus on clinical outcome.