The human genome puzzle - the role of copy number variation in somatic mosaicism.

The discovery of copy number variations (CNV) in the human genome opened new perspectives in the study of the genetic causes of inherited disorders and the etiology of common diseases. Differently patterned instances of somatic mosaicism in CNV regions have been shown to be present in monozygotic twins and throughout different tissues within an individual. A single-cell-level investigation of CNV in different human cell types led us to uncover mitotically derived genomic mosaicism, which is stable in different cell types of one individual. A unique study of immortalized B-lymphoblastoid cell lines obtained with 20 year interval from the same two subjects shows that mitotic changes in CNV regions may happen early during embryonic development and seem to occur only once, as levels of mosaicism remained stable. This finding has the potential to change our concept of dynamic human genome variation. We propose that further genomic studies should focus on the single-cell level, to understand better the etiology and physiology of aging and diseases mediated by somatic variations.