Phenotypic spectrum in osteogenesis imperfecta due to mutations in TMEM38B: unravelling a complex cellular defect

Emma Webb, Meena Balasubramanian, Nadja Fratzl-Zelman, Wayne A Cabral, Hannah Titherage, Atif Alsaedi, Vrinda Saraff, Julie Vogt, Trevor Cole, Susan Stewart, Nicola Crabtree, Brandi M Sargent, Sonja Gamsjaeger, Eleftherios P. Paschalis, Paul Roschger, Klaus Klaushofer, Nick J. Shaw, Joan C Marini, Wolfgang Högler

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13 Citations (Scopus)
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Abstract

Context: Recessive mutations in TMEM38B cause type XIV osteogenesis imperfecta (OI) by dysregulating intracellular calcium flux. Objectives: Clinical and bone material phenotype description and osteoblast differentiation studies. Design and Setting: Natural history study in pediatric research centers. Patients: Eight patients with type XIV OI. Main Outcome Measures: Clinical examinations included bone mineral density, radiographs, echocardiography, and muscle biopsy. Bone biopsy samples (n = 3) were analyzed using histomorphometry, quantitative backscattered electron microscopy, and Raman microspectroscopy. Cellular differentiation studies were performed on proband and control osteoblasts and normal murine osteoclasts. Results: Type XIV OI clinical phenotype ranges from asymptomatic to severe. Previously unreported features include vertebral fractures, periosteal cloaking, coxa vara, and extraskeletal features (muscular hypotonia, cardiac abnormalities). Proband lumbar spine bone density z score was reduced [median −3.3 (range −4.77 to +0.1; n = 7)] and increased by +1.7 (1.17 to 3.0; n = 3) following bisphosphonate therapy. TMEM38B mutant bone has reduced trabecular bone volume, osteoblast, and particularly osteoclast numbers, with >80% reduction in bone resorption. Bone matrix mineralization is normal and nanoporosity low. We demonstrate a complex osteoblast differentiation defect with decreased expression of early markers and increased expression of late and mineralization-related markers. Predominance of trimeric intracellular cation channel type B over type A expression in murine osteoclasts supports an intrinsic osteoclast defect underlying low bone turnover. Conclusions: OI type XIV has a bone histology, matrix mineralization, and osteoblast differentiation pattern that is distinct from OI with collagen defects. Probands are responsive to bisphosphonates and some show muscular and cardiovascular features possibly related to intracellular calcium flux abnormalities.
Original languageEnglish
Pages (from-to)2019-2028
JournalThe Journal of clinical endocrinology and metabolism
Volume102
Issue number6
Early online date16 Mar 2017
DOIs
Publication statusPublished - 1 Jun 2017

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