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Hum Genet. 2018 Jul;137(6-7):511-520. doi: 10.1007/s00439-018-1904-1. Epub 2018 Jul 10.

Extreme clustering of type-1 NF1 deletion breakpoints co-locating with G-quadruplex forming sequences.

Author information

1
Institute of Human Genetics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
2
Department of Neurology, University Hospital Hamburg Eppendorf, 20246, Hamburg, Germany.
3
Institute of Medical Genetics, School of Medicine, Cardiff University, Cardiff, CF14 4XN, UK.
4
Center for Medical Genetics Ghent, Ghent University Hospital, Ghent, Belgium.
5
Department of Genetics, University of Alabama at Birmingham, Birmingham, USA.
6
Institute of Human Genetics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany. hildegard.kehrer-sawatzki@uni-ulm.de.

Abstract

The breakpoints of type-1 NF1 deletions encompassing 1.4-Mb are located within NF1-REPa and NF1-REPc, which exhibit a complex structure comprising different segmental duplications in direct and inverted orientation. Here, we systematically assessed the proportion of type-1 NF1 deletions caused by nonallelic homologous recombination (NAHR) and those mediated by other mutational mechanisms. To this end, we analyzed 236 unselected type-1 deletions and observed that 179 of them (75.8%) had breakpoints located within the NAHR hotspot PRS2, whereas 39 deletions (16.5%) had breakpoints located within PRS1. Sixteen deletions exhibited breakpoints located outside of these NAHR hotspots but were also mediated by NAHR. Taken together, the breakpoints of 234 (99.2%) of the 236 type-1 NF1 deletions were mediated by NAHR. Thus, NF1-REPa and NF1-REPc are strongly predisposed to recurrent NAHR, the main mechanism underlying type-1 NF1 deletions. We also observed a non-random overlap between type-1 NF1-deletion breakpoints and G-quadruplex forming sequences (GQs) as well as regions flanking PRDM9A binding-sites. These findings imply that GQs and PRDM9A binding-sites contribute to the clustering of type-1 deletion breakpoints. The co-location of both types of sequence was at its highest within PRS2, indicative of their synergistic contribution to the greatly increased NAHR activity within this hotspot.

PMID:
29992513
DOI:
10.1007/s00439-018-1904-1
[Indexed for MEDLINE]

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