title: Recessive osteogenesis imperfecta caused by missense mutations in SPARC.
abstract: Secreted protein, acidic, cysteine-rich (SPARC) is a glycoprotein that binds to collagen type I and other proteins in the extracellular matrix. Using whole-exome sequencing to identify the molecular defect in two unrelated girls with severe bone fragility and a clinical diagnosis of osteogenesis imperfecta type IV, we identified two homozygous variants in SPARC (GenBank: NM_003118.3; c.497G>A [p.Arg166His] in individual 1; c.787G>A [p.Glu263Lys] in individual 2). Published modeling and site-directed mutagenesis studies had previously shown that the residues substituted by these mutations form an intramolecular salt bridge in SPARC and are essential for the binding of SPARC to collagen type I. The amount of SPARC secreted by skin fibroblasts was reduced in individual 1 but appeared normal in individual 2. The migration of collagen type I alpha chains produced by these fibroblasts was mildly delayed on SDS-PAGE gel, suggesting some overmodification of collagen during triple helical formation. Pulse-chase experiments showed that collagen type I secretion was mildly delayed in skin fibroblasts from both individuals. Analysis of an iliac bone sample from individual 2 showed that trabecular bone was hypermineralized on the material level. In conclusion, these observations show that homozygous mutations in SPARC can give rise to severe bone fragility in humans.
authors.affiliation: Department of Paediatrics, Division of Clinical and Metabolic Genetics, The Hospital for Sick Children and University of Toronto, Toronto, ON M5G 1X8, Canada; The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
authors.forename: Roberto
authors.initials: R
authors.lastname: Mendoza-Londono
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montréal, QC H3A 1B1, Canada.
authors.forename: Somayyeh
authors.initials: S
authors.lastname: Fahiminiya
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montréal, QC H3A 1B1, Canada.
authors.forename: Jacek
authors.initials: J
authors.lastname: Majewski
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montréal, QC H3A 1B1, Canada.
authors.forename: Martine
authors.initials: M
authors.lastname: Tétreault
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montréal, QC H3A 1B1, Canada.
authors.forename: Javad
authors.initials: J
authors.lastname: Nadaf
authors.affiliation: Department of Paediatrics, Division of Clinical and Metabolic Genetics, The Hospital for Sick Children and University of Toronto, Toronto, ON M5G 1X8, Canada; The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Kannu
authors.affiliation: The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; Division of Endocrinology, Department of Paediatrics, The Hospital for Sick Children and University of Toronto, Toronto, ON M5G 1X8, Canada.
authors.forename: Etienne
authors.initials: E
authors.lastname: Sochett
authors.affiliation: The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; Department of Orthopaedic Surgery, The Hospital for Sick Children and The University of Toronto, Toronto, ON M5G 1X8, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Howard
authors.affiliation: The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; Department of Diagnostic Imaging, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Stimec
authors.affiliation: Department of Paediatrics, Division of Clinical and Metabolic Genetics, The Hospital for Sick Children and University of Toronto, Toronto, ON M5G 1X8, Canada; The Bone Health Centre, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
authors.forename: Lucie
authors.initials: L
authors.lastname: Dupuis
authors.affiliation: Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Center Meidling, 1st Med. Department, Hanusch Hospital, Vienna 1140, Austria.
authors.forename: Paul
authors.initials: P
authors.lastname: Roschger
authors.affiliation: Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Center Meidling, 1st Med. Department, Hanusch Hospital, Vienna 1140, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Klaushofer
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada.
authors.forename: Telma
authors.initials: T
authors.lastname: Palomo
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Ouellet
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada.
authors.forename: Hadil
authors.initials: H
authors.lastname: Al-Jallad
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada.
authors.forename: John S
authors.initials: JS
authors.lastname: Mort
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Moffatt
authors.affiliation: Shriners Hospital for Children, Portland, OR 97239, USA.
authors.forename: Sergei
authors.initials: S
authors.lastname: Boudko
authors.affiliation: Shriners Hospital for Children, Portland, OR 97239, USA.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Bächinger
authors.affiliation: Shriners Hospital for Children, Montréal, QC H3G 1A6, Canada. Electronic address: frauch@shriners.mcgill.ca.
authors.forename: Frank
authors.initials: F
authors.lastname: Rauch
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D024042:Collagen Type I / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D059472:Exome / Q000235:genetics; D005260:Female; D005808:Genes, Recessive / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense / Q000235:genetics*; D010013:Osteogenesis Imperfecta / Q000235:genetics* / Q000473:pathology*; D015676:Osteonectin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D010375:Pedigree; D011487:Protein Conformation; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D024042:Collagen Type I; D015676:Osteonectin; C577241:SPARC protein, human