Non-allelic homologous recombination

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Non-allelic homologous recombination (NAHR) is a form of homologous recombination that occurs between two lengths of DNA that have high sequence similarity, but are not alleles.[1][2][3]

It usually occurs between sequences of DNA that have been previously duplicated through evolution, and therefore have low copy repeats (LCRs). These repeat elements typically range from 10–300 kb in length and share 95-97% sequence identity.[4] During meiosis or mitosis, LCRs can misalign and subsequent crossing-over can result in genetic rearrangement.[4] When non-allelic homologous recombination occurs between different LCRs, deletions or further duplications of the DNA can occur. This can give rise to rare genetic disorders, caused by the loss or increased copy number of genes within the deleted or duplicated region. It can also contribute to the copy number variation seen in some gene clusters.[5]

As LCRs are often found in "hotspots" in the human genome, some chromosomal regions are particularly prone to NAHR.[1] Recurrent rearrangements are nucleotide sequence variations found in multiple individuals, sharing a common size and location of break points.[4] Therefore, multiple patients may manifest with similar deletions or duplications, resulting in the description of genetic syndromes. Examples of these include NF1 microdeletion syndrome, 17q21.3 recurrent microdeletion syndrome or 3q29 microdeletion syndrome.[6][7][8]

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  1. ^ a b Hurles, Matthew; et al. (2006), "Recombination Hotspots in Nonallelic Homologous Recombination", Genomic Disorders: The Genomic Basis of Disease, Humana Press, pp. 341–355 
  2. ^ Beckmann JS, Estivill X, Antonarakis SE (August 2007). "Copy number variants and genetic traits: closer to the resolution of phenotypic to genotypic variability". Nat. Rev. Genet. 8 (8): 639–46. PMID 17637735. doi:10.1038/nrg2149. 
  3. ^ Colnaghi, Rita (July 2011). "The consequences of structural genomic alterations in humans: Genomic Disorders, genomic instability and cancer". Seminars in Cell & Developmental Biology. 22: 875–885. doi:10.1016/j.semcdb.2011.07.010. 
  4. ^ a b c Colnaghi, Rita; Carpenter, Gillian; Volker, Marcel; O’Driscoll, Mark (2011-10-01). "The consequences of structural genomic alterations in humans: Genomic Disorders, genomic instability and cancer". Seminars in Cell & Developmental Biology. Polarized growth and movement: How to generate new shapes and structuresChromosome Recombination. 22 (8): 875–885. doi:10.1016/j.semcdb.2011.07.010. 
  5. ^ Karn RC, Laukaitis CM (2009). "The mechanism of expansion and the volatility it created in three pheromone gene clusters in the mouse (Mus musculus) genome". Genome Biol Evol. 1: 494–503. PMC 2839280Freely accessible. PMID 20333217. doi:10.1093/gbe/evp049. 
  6. ^ Venturin M, Gervasini C, Orzan F, et al. (June 2004). "Evidence for non-homologous end joining and non-allelic homologous recombination in atypical NF1 microdeletions". Hum. Genet. 115 (1): 69–80. PMID 15103551. doi:10.1007/s00439-004-1101-2. 
  7. ^ Koolen DA, Sharp AJ, Hurst JA, et al. (November 2008). "Clinical and molecular delineation of the 17q21.31 microdeletion syndrome". J. Med. Genet. 45 (11): 710–20. PMC 3071570Freely accessible. PMID 18628315. doi:10.1136/jmg.2008.058701. 
  8. ^ Willatt L, Cox J, Barber J, et al. (July 2005). "3q29 microdeletion syndrome: clinical and molecular characterization of a new syndrome". Am. J. Hum. Genet. 77 (1): 154–60. PMC 1226188Freely accessible. PMID 15918153. doi:10.1086/431653.