Editing Chromosomal translocation (section)

==Nonreciprocal translocation==

Nonreciprocal translocation is a chromosomal abnormality that involves the one-way transfer of [[genes]] from one [[chromosome]] to another [[Non-homologous recombination|non-homologous]] chromosome. This transfer will always be unbalanced resulting in genetic imbalance. This excess or deletion of genetic material compared to a normal genome is likely to result in disease.

Nonreciprocal translocations can occur as a result of three main processes. Errors during [[DNA replication]], unequal [[Chromosomal crossover|crossing over]] in meiosis or mitosis and/or exogenous factors causing double stranded DNA damage.<ref name=":12">{{Cite journal |last1=Ali |first1=Hanif |last2=Daser |first2=Angelika |last3=Dear |first3=Paul |last4=Wood |first4=Henry |last5=Rabbitts |first5=Pamela |last6=Rabbitts |first6=Terence |date=2013 |title=Nonreciprocal chromosomal translocations in renal cancer involve multiple DSBs and NHEJ associated with breakpoint inversion but not necessarily with transcription |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/gcc.22038 |journal=Genes, Chromosomes and Cancer |language=en |volume=52 |issue=4 |pages=402–409 |doi=10.1002/gcc.22038 |pmid=23341332 |issn=1098-2264|url-access=subscription }}</ref> When a chromosome experiences a double strand break at one or more locations it may rejoin to a non-homologous chromosome.<ref name=":12" /> In the case of nonreciprocal translocations, the acceptor chromosome gains material but the donor chromosome does not accept material in exchange. This unequal transfer causes loss of genetic material which may have varying degrees of impact.

A number of factors affect the impact of the translocation. The segment of the chromosome affected by the double strand break may be in a coding or noncoding region.<ref name=":13">{{Cite journal |last1=Nikitin |first1=Dmitri |last2=Tosato |first2=Valentina |last3=Zavec |first3=Apolonija Bedina |last4=Bruschi |first4=Carlo V. |date=2008-07-15 |title=Cellular and molecular effects of nonreciprocal chromosome translocations in Saccharomyces cerevisiae |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=28 |pages=9703–9708 |doi=10.1073/pnas.0800464105 |doi-access=free |pmc=2474487 |pmid=18599460|bibcode=2008PNAS..105.9703N }}</ref> Therefore, the rearrangement may result in a number of affects to the gene. Essential genes may be silenced or [[oncogene]]s may be activated.<ref name=":13" /> The chromosome on which the translocation occurs may also affect the result due to certain chromosomes containing more [[essential gene]]s. Which cell type the translocation occurs in may also have an affect. [[Somatic cell]]s are more likely to result in cancer, where [[germ line cell]]s are more likely to result in birth defects including miscarriages and still births.<ref>{{cite journal |last1=Nambiar |first1=Mridula |last2=Kari |first2=Vijayalakshmi |last3=Raghavan |first3=Sathees C. |title=Chromosomal translocations in cancer |journal=Biochimica et Biophysica Acta (BBA) - Reviews on Cancer |date=December 2008 |volume=1786 |issue=2 |pages=139–152 |doi=10.1016/j.bbcan.2008.07.005 |pmid=18718509 }}</ref>

One specific example of an unbalanced nonreciprocal translocation is [[Emanuel syndrome|Emanuel Syndrome]]. At the chromosomal level, a fragment from chromosome 11 is non-reciprocally translocated to chromosome 22 creating genetic imbalances.<ref name=":9" /> Phenotypically, Emanuel Syndrome presents as neurological and physical developmental disorders, [[microcephaly]], and [[congenital defects]].<ref name=":9" />