Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse, Jena, Germany
*Corresponding author Email: Thomas.Liehr@med.uni-jena.de
Copy number variations are nowadays most often understood as submicroscopic gains or losses of chromosomal material, either connected with a disease or just one of the many possible genetic variants in man. However, besides such submicroscopic copy number variations,already decades ago chromosome analysis revealed the existence of cytogenetic visible copy number variations; first discovered were the chromosomal heteromorphisms, more recently euchromatic variants and unbalanced chromosome abnormalities without phenotypic consequences. Recently, for submicroscopic copy number variations a so-called two-hit model suggested. This suggests that the combination of per se harmless size variants may be led to clinical aberrations if they are present together in a patient.
A literature based comparison of cytogenetic visible copy number variations and MG-CNVs revealed that, biologically, besides size, these two groups of copy number variations do not really differ. Both may be present as heterochromatic (gene-poor to gene-free) and euchromatic copy number variation-variants. Identical regions have even been reported as cytogenetic visible copy number variation and a submicroscopic copy number variationsindependently. This study reviews the differences between submicroscopic and microscopically visible CNVs.
Yet cytogenetic visible copy number variations, especially chromosomal heteromorphisms are by far not considered enough in evaluation of routine cytogenetic analysis as well as in array-based comparative genomic hybridisation analysis.