Intercellular genomic (chromosomal) variations resulting in somatic mosaicism: Mechanisms and consequences

Large-scale variations of the human genome can be produced by losses or gains of whole chromosomes (aneuploidy). In contrast to DNA sequences variations at subchromosomal level (single nucleotide polymorphisms, short tandem repeat variations) or interindividual subtle chromosome region changes (deletions, duplications, large-scale copy-number variants, fragile sites), aneuploidy simultaneously involves hundreds or even thousands of genes and, therefore, dramatically affects functional genome activity. Aneuploidy originates from either meiotic or mitotic chromosome instability and, in some instances, manifests as somatic chromosomal mosaicism. Although the real incidence of mosaic aneuploidy in somatic human tissues remains to be determined, one can suppose an overlooked fraction of cells with unshared genomes due to large-scale genomic alterations among 10(14) cells forming the human body. Intercellular differences in chromosome number can be considered an overlooked type of structural and functional genome variations, which produce genetic mosaicism. This review refers to somatic chromosomal mosaicism and aims to describe its mechanisms and consequences. Moreover, the effect of somatic chromosomal mosaicism on both interindividual and intercellular diversity as well as human diseases is discussed. Finally, since the identification of these genomic variations faces numerous difficulties, we found pertinent to describe available approaches towards the detection of chromosomal mosaicism in human somatic tissues.