title: Paget's disease of bone in the French population: novel SQSTM1 mutations, functional analysis, and genotype-phenotype correlations.
abstract: Mutation screening of the SQSTM1 gene in 94 French patients with PDB revealed two novel point-mutations (A381V and L413F) and two new compound heterozygous genotypes (P392L/A381V and P392L/A390X). Functional analysis showed an increased level of SQSTM1/p62 protein in PDB patients and truncated forms of the protein encoded by the A390X allele. Clinical data indicate that PDB patients with SQSTM1 mutation are younger at PDB diagnosis and have more extensive bone lesions.
  
  
  BACKGROUND
  Paget's disease of bone (PDB) is a common chronic disease of the skeleton, with a strong genetic component. A recurrent mutation (P392L) was first identified on chromosome 5, in the Sequestosome 1 (SQSTM1) gene. Several other mutations of the SQSTM1 gene have been described in PDB patients, affecting the ubiquitin-associated domain (UBA) of the SQSTM1/p62 protein. The objectives of this study were to evaluate the frequency of the SQSTM1 mutations in French PBD patients, to study the expression of the SQSTM1/p62 protein, and to search for genotype-phenotype correlations.
  
  
  METHODS
  Blood was obtained from 94 unrelated French PDB patients and 100 controls for mutation screening of exons 7 and 8, encoding for the UBA domain of SQSTM1. Epstein-Barr virus (EBV)-immortalized B-cell lymphocytes were established from 13 patients, giving access to functional analysis of the gene and the SQSTM1/p62 expressions using real-time PCR and Western blot.
  
  
  RESULTS
  Mutations of the SQSTM1 gene were identified in 12 of the 94 PDB patients (13%). Eight patients carried P392L. Two novel missense mutations were identified: L413F and A381V. This A381V mutation and A390X were found in distinct patients already carriers of P392L. The SQSTM1/p62 protein expression in PDB patients increased when zero, one, or two mutations were present, and SQSTM1 truncated forms were associated with the A390X mutation. The mean age of PDB diagnosis was younger in patients with the SQSTM1 mutation. PDB was more extensive in patients who carried a SQSTM1 mutation.
  
  
  CONCLUSIONS
  Mutations of SQSTM1 are present in the French population. PDB patients with and without the SQSTM1 mutation have an increased level of SQSTM1/p62, caused by overproduction of the protein, probably involved in the pathophysiology of PDB. The presence of the SQSTM1 mutation may be a worsening factor for PDB.
authors.affiliation: Hôpital Lariboisière, Paris, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Collet
authors.forename: Laëtitia
authors.initials: L
authors.lastname: Michou
authors.forename: Maurice
authors.initials: M
authors.lastname: Audran
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Chasseigneaux
authors.forename: Pascal
authors.initials: P
authors.lastname: Hilliquin
authors.forename: Thomas
authors.initials: T
authors.lastname: Bardin
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lemaire
authors.forename: François
authors.initials: F
authors.lastname: Cornélis
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Launay
authors.forename: Philippe
authors.initials: P
authors.lastname: Orcel
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Laplanche
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001483:Base Sequence; D015153:Blotting, Western; D002461:Cell Line, Transformed; D017931:DNA Primers; D005602:France / Q000453:epidemiology; D005838:Genotype; D006801:Humans; D009154:Mutation; D010001:Osteitis Deformans / Q000453:epidemiology* / Q000235:genetics; D010641:Phenotype; D011506:Proteins / Q000235:genetics*; D000071456:Sequestosome-1 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; D011506:Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein