title: Evaluation of somatic mutations in tibial pseudarthrosis samples in neurofibromatosis type 1.
abstract: BACKGROUND
  Tibial pseudarthrosis is associated with neurofibromatosis type 1 (NF1) and there is wide clinical variability of the tibial dysplasia in NF1, suggesting the possibility of genetic modifiers. Double inactivation of NF1 is postulated to be necessary for the development of tibial pseudarthrosis, but tissue or cell of origin of the 'second hit' mutation remains unclear.
  
  
  METHODS
  Exome sequencing of different sections of surgically resected NF1 tibial pseudarthrosis tissue was performed and compared to germline (peripheral blood).
  
  
  RESULTS
  A germline NF1 splice site mutation (c.61-2A>T, p.L21 M68del) was identified from DNA extracted from peripheral blood. Exome sequencing of DNA extracted from tissue removed during surgery of the tibial pseudarthrosis showed a somatic mutation of NF1 (c.3574G>T, p.E1192*) in the normal germline allele. Further analysis of different regions of the tibial pseudarthrosis sample showed enrichment of the somatic mutation in the soft tissue within the pseudarthrosis site and absence of the somatic mutation in cortical bone. In addition, a germline variant in PTPN11 (c.1658C>T, p.T553M), a gene involved in the RAS signal transduction pathway was identified, although the clinical significance is unknown.
  
  
  CONCLUSIONS
  Given that the NF1 somatic mutation was primarily detected in the proliferative soft tissue at the pseudarthrosis site, it is likely that the second hit occurred in mesenchymal progenitors from the periosteum. These results are consistent with a defect of differentiation, which may explain why the mutation is found in proliferative cells and not within cortical bone tissue, as the latter by definition contains mostly mature differentiated osteoblasts and osteocytes.
authors.affiliation: ARUP Laboratories, ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA.
authors.forename: David W
authors.initials: DW
authors.lastname: Sant
authors.affiliation: ARUP Laboratories, ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Margraf
authors.affiliation: Department of Pediatrics, Division of Medical Genetics, Stanford University, Stanford, California, USA Departments of Pediatrics, Division of Medical Genetics, University of Utah, School of Medicine, Salt Lake City, Utah, USA Shriners Hospital for Children Salt Lake City, Salt Lake City, Utah, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Stevenson
authors.affiliation: ARUP Laboratories, ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA Department of Pathology, University of Utah, School of Medicine, Salt Lake City, Utah, USA.
authors.forename: Allie H
authors.initials: AH
authors.lastname: Grossmann
authors.affiliation: Departments of Pediatrics, Division of Medical Genetics, University of Utah, School of Medicine, Salt Lake City, Utah, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Viskochil
authors.affiliation: Departments of Pediatrics, Division of Medical Genetics, University of Utah, School of Medicine, Salt Lake City, Utah, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Hanson
authors.affiliation: Departments of Pediatrics, Division of Medical Genetics, University of Utah, School of Medicine, Salt Lake City, Utah, USA.
authors.forename: Melanie D
authors.initials: MD
authors.lastname: Everitt
authors.affiliation: Sarah M. and Charles E. Seay Center for Musculoskeletal Research, Texas Scottish Rite Hospital for Children, Dallas, Texas, USA Department of Pediatrics, UT Southwestern Medical Center, Dallas, Texas, USA Eugene McDermott Center for Human Growth and Development and UT Southwestern Medical Center, Dallas, Texas, USA Department of Orthopaedic Surgery, UT Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Rios
authors.affiliation: Vanderbilt Center for Bone Biology; Vanderbilt University Medical Center, Nashville, Tennessee, USA Departments of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA Departments of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee, USA Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Florent
authors.initials: F
authors.lastname: Elefteriou
authors.affiliation: Shriners Hospital for Children Salt Lake City, Salt Lake City, Utah, USA.
authors.forename: Theresa
authors.initials: T
authors.lastname: Hennessey
authors.affiliation: ARUP Laboratories, ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA Department of Pathology, University of Utah, School of Medicine, Salt Lake City, Utah, USA.
authors.forename: Rong
authors.initials: R
authors.lastname: Mao
mesh_terms: D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D016514:Genes, Neurofibromatosis 1; D006801:Humans; D009154:Mutation; D009456:Neurofibromatosis 1 / Q000235:genetics*; D011542:Pseudarthrosis / Q000235:genetics*; D011859:Radiography; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology*
keywords: PTPN11; bone; neurofibromatosis type 1; pseudarthrosis; somatic mutation