CHROMOSOMAL MOSAICISM AS A REASON OF DEVELOPMENTAL DISORDERS IN HUMAN. PART I. MECHANISMS OF FORMATION

The chromosomal mosaicism connected with unbalanced karyotype due to numeric and structural chromosome aberrations may be a reason of the developmental disorders or by the presence of chromosome instability manifesting in some monogenic disorders in human. The mechanisms of formation the mosaicism like the postzygotic nondisjunction, anaphase lagging, postzygotic duplication, disturbances of protein function of genes responsible for repair of double-strand DNA breaks and control cell divisions, the genes controlling the separation of sisters chromatid or telomere length have been presented. In addition the hot spots - LCR (low copy repeats) as the predisposing factor of illegitimate somatic recombination responsible for chromosome breakage and chromosomal rearrangements were also considered. The specific form of mosaicism leading to developmental disturbances due to genomic imprinting of some genes being in disomy state of entire or segments of chromosomes were taken also into consideration.