Mutations in known monogenic high bone mass loci only explain a small proportion of high bone mass cases

Gregson, Celia L., Wheeler, Lawrie, Hardcastle, Sarah A., Appleton, Louise H., Addison, Kathryn A., Brugmans, Marieke, Clark, Graeme R., Ward, Kate A., Paggiosi, Margaret, Stone, Mike, Thomas, Joegi, Agarwal, Rohan, Poole, Kenneth E.S., McCloskey, Eugene, Fraser, William D., Williams, Eleanor, Bullock, Alex N., Davey Smith, George, Brown, Matthew A., Tobias, Jon H., & Duncan, Emma L. (2016) Mutations in known monogenic high bone mass loci only explain a small proportion of high bone mass cases. Journal of Bone and Mineral Research, 31(3), pp. 640-649.

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Abstract

High bone mass (HBM) can be an incidental clinical finding; however, monogenic HBM disorders (eg, LRP5 or SOST mutations) are rare. We aimed to determine to what extent HBM is explained by mutations in known HBM genes. A total of 258 unrelated HBM cases were identified from a review of 335,115 DXA scans from 13 UK centers. Cases were assessed clinically and underwent sequencing of known anabolic HBM loci: LRP5 (exons 2, 3, 4), LRP4 (exons 25, 26), SOST (exons 1, 2, and the van Buchem's disease [VBD] 52-kb intronic deletion 3'). Family members were assessed for HBM segregation with identified variants. Three-dimensional protein models were constructed for identified variants. Two novel missense LRP5 HBM mutations ([c.518C>T; p.Thr173Met], [c.796C>T; p.Arg266Cys]) were identified, plus three previously reported missense LRP5 mutations ([c.593A>G; p.Asn198Ser], [c.724G>A; p.Ala242Thr], [c.266A>G; p.Gln89Arg]), associated with HBM in 11 adults from seven families. Individuals with LRP5 HBM ( approximately prevalence 5/100,000) displayed a variable phenotype of skeletal dysplasia with increased trabecular BMD and cortical thickness on HRpQCT, and gynoid fat mass accumulation on DXA, compared with both non-LRP5 HBM and controls. One mostly asymptomatic woman carried a novel heterozygous nonsense SOST mutation (c.530C>A; p.Ser177X) predicted to prematurely truncate sclerostin. Protein modeling suggests the severity of the LRP5-HBM phenotype corresponds to the degree of protein disruption and the consequent effect on SOST-LRP5 binding. We predict p.Asn198Ser and p.Ala242Thr directly disrupt SOST binding; both correspond to severe HBM phenotypes (BMD Z-scores +3.1 to +12.2, inability to float). Less disruptive structural alterations predicted from p.Arg266Cys, p.Thr173Met, and p.Gln89Arg were associated with less severe phenotypes (Z-scores +2.4 to +6.2, ability to float). In conclusion, although mutations in known HBM loci may be asymptomatic, they only account for a very small proportion ( approximately 3%) of HBM individuals, suggesting the great majority are explained by either unknown monogenic causes or polygenic inheritance.

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ID Code: 94200
Item Type: Journal Article
Refereed: Yes
Keywords: LRP5; SOST; ANABOLIC; SEQUENCING; PROTEIN MODELING
DOI: 10.1002/jbmr.2706
ISSN: 1523-4681
Divisions: Current > QUT Faculties and Divisions > Faculty of Education
Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 2015 The Authors
Copyright Statement: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Deposited On: 23 Mar 2016 02:03
Last Modified: 24 Mar 2016 01:48

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