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Cytogenetic studies of chromosomal breakage diseases

Chromosome breaks occur either as a result of damage to DNA (by e.g. radiation or chemicals) or as part of the mechanism of recombination. In G2 phase of the cell cycle chromosomes breaks occurring at this stage are manifested as chromatid breaks while breaks that is occurring in G1 phase, appear later as chromosome breaks. The chromosomal breakage may disrupt an important gene or the break may affect expression of a gene even though it does not disrupt the coding sequence. It may separate a gene from a control element, or it may put the gene in an inappropriate chromatin environment. The aim of this review is to outline the different chromosome breakage disorders and methods for their detection. Numerous genetic syndromes are marked by chromosome instability, that are strikingly associated with various cancers. They represent a group of autosomal recessive heritable disorders that share the common characteristics of increased spontaneous or induced chromosomal breakage. Among these diseases are Fanconi anemia, ataxia telangectasia, Nijmegen breakage syndrome, Bloom syndrome, Werner syndrome and Rothmund-Thompson syndrome. In addition to the classical chromosomal breakage syndromes, there are several other disorders that exhibit chromosomal breakage and instabilities. Cancer is one of a major group that shows chromosomal instability also, other diseases such as chronic inflammatory disease, neurodegenerative disorders. Mitochondrial disease may show instability but not as a constant feature of the disease. In conclusion several cytogenetic techniques have been emerged to detect the chromosomal breakage and instabilities, such as sister chromatid exchange, fluorescent in situ hybridization, micronucleus and comet assay. It is important to properly choose the cytogenetic test according to the disease to be investigated. Analysis of the results could be very helpful in the diagnosis and management of cases