title: Evidence for non-homologous end joining and non-allelic homologous recombination in atypical NF1 microdeletions.
abstract: NF1 microdeletion syndrome is caused by haploinsufficiency of the NF1 gene and of gene(s) located in adjacent flanking regions. Most of the NF1 deletions originate by non-allelic homologous recombination between repeated sequences (REP-P and -M) mapped to 17q11.2, while the remaining deletions show unusual breakpoints. We performed high-resolution FISH analysis of 18 NF1 microdeleted patients with the aims of mapping non-recurrent deletion breakpoints and verifying the presence of additional recombination-prone architectural motifs. This approach allowed us to obtain the sequence of the first junction fragment of an atypical deletion. By conventional FISH, we identified 16 patients with REP-mediated common deletions, and two patients carrying atypical deletions of 1.3 Mb and 3 Mb. Following fibre-FISH, we identified breakpoint regions of 100 kb, which led to the generation of several locus-specific probes restricting the atypical deletion endpoint intervals to a few kilobases. Sequence analysis provided evidence of small blocks of REPs, clustered around the 1.3-Mb deletion breakpoints, probably involved in intrachromatid non-allelic homologous recombination (NAHR), while isolation and sequencing of the 3-Mb deletion junction fragment indicated that a non-homologous end joining (NHEJ) mechanism is implicated.
authors.affiliation: Department of Biology and Genetics, Medical Faculty, University of Milan, via Viotti 3/5, 20133, Milan, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Venturin
authors.forename: Cristina
authors.initials: C
authors.lastname: Gervasini
authors.forename: Francesca
authors.initials: F
authors.lastname: Orzan
authors.forename: Angela
authors.initials: A
authors.lastname: Bentivegna
authors.forename: Lucia
authors.initials: L
authors.lastname: Corrado
authors.forename: Patrizia
authors.initials: P
authors.lastname: Colapietro
authors.forename: Alessandra
authors.initials: A
authors.lastname: Friso
authors.forename: Romano
authors.initials: R
authors.lastname: Tenconi
authors.forename: Meena
authors.initials: M
authors.lastname: Upadhyaya
authors.forename: Lidia
authors.initials: L
authors.lastname: Larizza
authors.forename: Paola
authors.initials: P
authors.lastname: Riva
mesh_terms: D001483:Base Sequence; D019457:Chromosome Breakage; D002886:Chromosomes, Human, Pair 17; D017353:Gene Deletion; D016514:Genes, Neurofibromatosis 1; D055614:Genetic Phenomena; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D009456:Neurofibromatosis 1 / Q000235:genetics*; D020161:Physical Chromosome Mapping; D011995:Recombination, Genetic