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The Journal of Clinical Endocrinology & Metabolism 90(12):6392– 6395 Copyright © 2005 by The Endocrine Society doi: 10.1210/jc.2005-1235
Bone Mineral Density in Sclerosteosis; Affected Individuals and Gene Carriers Jessica C. Gardner, Rutger L. van Bezooijen, Benjamin Mervis, Neveen A. T. Hamdy, Clemens W. G. M. Lo¨wik, Herman Hamersma, Peter Beighton, and Socrates E. Papapoulos Division of Human Genetics, Faculty of Health Sciences, University of Cape Town (J.C.G., P.B., B.M.), Observatory 7925, Cape Town, South Africa; Flora Clinic (H.H.), Roodepoort, Gauteng 1709, South Africa; and Departments of Endocrinology and Metabolic Diseases (R.L.v.B., N.A.T.H., C.W.G.M.L., S.E.P.) and Molecular Cell Biology (R.L.v.B.), Leiden University Medical Center, 2333 ZA, Leiden, The Netherlands Background: Sclerosteosis is an autosomal recessive sclerosing bone disorder due to deficiency of sclerostin, a protein secreted by the osteocytes that inhibits bone formation. In the present study we assessed the effect of variable expression of the genetic defect on bone mineral density (BMD) in patients and carriers of the determinant gene. Methods: We studied 25 individuals (seven patients and 18 phenotypically normal heterozygotes). BMD was measured by dual x-ray absorptiometry at the lumbar spine, total hip, and distal forearm, and lateral radiographs of the skull were obtained. Results: Individuals with sclerosteosis had markedly increased BMD at all skeletal sites (Z-score ranges: lumbar spine, ⫹7.73 to ⫹14.43; total hip, ⫹7.84 to ⫹11.51; forearm, ⫹4.44 to ⫹9.53). In heterozy-
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CLEROSTEOSIS IS A rare skeletal dysplasia characterized by progressive bone thickening and sclerosis of the skeleton, especially of the skull, resulting in enlargement of the jaw, facial distortion, raised intracranial pressure, and entrapment of cranial nerves with consequent facial palsy, hearing loss, and loss of smell (1– 4). Sudden death may result from impaction of the brainstem in the foramen magnum. The condition occurs mainly in Afrikaners, the white farmers who separated from the Dutch East India Co. and moved into the backcountry of South Africa. In this population, the estimated carrier rate of the determinant gene is approximately one in 100 individuals (5). A few affected individuals and families in other parts of the world have also been reported (4). Sclerosteosis is due to loss of function mutations of the SOST gene, which is located on chromosome 17q12–21 and encodes sclerostin, a protein produced by osteocytes that inhibits bone formation (6 –10). In patients with sclerosteosis and sclerostin deficiency, the bone phenotype is probably due to increased bone formation that is not associated with increased bone resorption, leading to a positive bone balance and increased bone mass (11). Bone specimens from affected individuals have a lamellar structure with predominance of cuboidal, active-appearing osteoblasts, increased doubleFirst Published Online September 27, 2005 Abbreviations: BMD, Bone mineral density; DXA, dual x-ray absorptiometry. JCEM is published monthly by The Endocrine Society (http://www. endo-society.org), the foremost professional society serving the endocrine community.
gotes, BMD was above the mean value of healthy age-matched individuals at all skeletal sites and had a wide range of normal and clearly increased values. Skull radiographs showed the typical hyperostotic changes in affected individuals and mild or no changes in heterozygotes. Conclusions: Heterozygous carriers of sclerosteosis have BMD values consistently higher than the mean of healthy subjects without any of the bone complications encountered in homozygotes. This finding suggests that the production and/or activity of sclerostin can be titrated in vivo, leading to variable increases in bone mass without any unwanted skeletal effects, a hypothesis of obvious significance for the development of new therapeutics for osteoporosis. (J Clin Endocrinol Metab 90: 6392– 6395, 2005)
tetracycline label spacing, and increased osteoid that mineralizes normally (9, 12, 13). There are no reports of fractures in patients with sclerosteosis (5). Sclerosteosis is inherited as an autosomal recessive trait, and heterozygous carriers of the disorder are clinically normal, although some may show age-related radiographic evidence of calvarial thickening (14). Despite recent progress in understanding the molecular basis of the condition, there has been no systematic evaluation of bone mineral density (BMD) in such patients and, in particular, in phenotypically normal heterozygotes. Such information can provide additional insight into the bone changes associated with the genetic defect that may lead to the development of novel therapies for patients with diseases characterized by low bone mass, such as osteoporosis. In the present study we addressed the question of whether one copy of the defective SOST gene, as present in asymptomatic carriers of the disease, has an effect on bone mass. Subjects and Methods We studied 25 individuals from six families with sclerosteosis. Seven individuals had the condition, and 18 were clinically normal relatives (parents, siblings, or children). None of the studied subjects had ever experienced a clinical fracture. Homozygosity and heterozygosity were documented by genotyping, which was performed by Dr. M. E. Brunkow (Celltech, Inc., Bothell, WA), as previously described (15). Lateral radiographs of the skull were obtained from all subjects. BMD of the lumbar spine, hip, and left forearm were measured by dual x-ray absorptiometry (DXA; Hologic QDR-1000, Waltham, MA). We used reference values for Caucasians provided by the manufacturer, because the Afrikaner population is of western European origin, whereas for the
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hip we used the National Health and Nutrition Examination Surveys III database. Results are expressed as grams per square centimeter or as Z-scores, i.e. the difference in sd from the mean of healthy subjects of the same age. Written informed consent was obtained from all adults, and parental consent was obtained for the children. The study was approved by the medical ethics committee of University of Cape Town.
Results Radiology
Representative lateral skull radiographs of a child and an adult patient with sclerosteosis and of a carrier of the disease are shown in Fig. 1. Radiographic features of the disease were already present at the age of 7 yr (Fig. 1A) and progressed to the characteristic changes of the condition in adulthood (Fig. 1B). The radiographs of the heterozygotes showed evidence of cranium thickening, with some loss of the diploid space (Fig. 1C). However, carriers could not always be clearly distinguished from healthy subjects. and no radiographic changes could be detected in younger carrier individuals. BMD
Affected individuals had markedly increased BMD at all skeletal sites (Table 1). The Z-scores ranged between ⫹7.73 and ⫹14.43 at the lumbar spine, between ⫹7.84 and ⫹11.51 at the total hip, and between ⫹4.44 and ⫹9.53 at the forearm. In heterozygous carriers, BMD Z-scores were above 0 at all skeletal sites and showed a wide range of normal or clearly increased values (Table 1). BMD Z-scores ranged between ⫹0.46 and ⫹5.15 at the lumbar spine, between ⫹0.37 and ⫹3.71 at the total hip, and between ⫹0.06 and ⫹2.73 at the forearm. The relation between BMD and age at the lumbar spine for patients and carriers is shown separately for males and females in Fig. 2. BMD values appear to follow a normal pattern, with increases in childhood and stabilization in young adults, but at a level higher than that in healthy subjects. Whether there is also a decline with ageing cannot be concluded due to the small number of individuals older than 50 yr. Discussion
Our study shows that individuals with sclerosteosis have markedly increased BMD at all skeletal sites examined, whereas heterozygous carriers have BMD values consistently higher than the mean of age-matched controls; these are either within the high normal range or clearly above it. However, there was no overlap of BMD values between the two groups of subjects. These findings are consistent with the phenotypes of the affected individuals, as well as with the skull radiographs that generally showed mild changes in heterozygotes. Despite the cross-sectional design of the study, our data suggest that bone mass increases only in the young patients and carriers, whereas it appears to stabilize in adulthood. Whether BMD also follows such a normal pattern later in life, i.e. decreases with age, cannot be answered in this study due to the limited availability of elderly subjects for testing. Longitudinal studies are needed to fully address these issues. This is the first systematic evaluation of BMD in families with sclerosteosis, and we cannot, therefore, compare our
FIG. 1. Lateral skull radiographs of a child (A) and an adult (B) with sclerosteosis and a heterozygote carrier (C) of the determinant gene.
findings with those from other studies of this disease. However, BMD measurements have been reported by other investigators in patients with van Buchem disease (hyperostosis corticalis generalisata familiaris), which closely resembles sclerosteosis (16, 17). Patients with van Buchem disease have radiological features similar to those of sclerosteosis, but the disorder runs a more benign course, and
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TABLE 1. Characteristics and BMD of homozygous and heterozygous subjects with sclerosteosis Subject no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Familya
Age (yr)
Sex
Status
U M W G M D D G G D U U G W G B B M M G M M M M M
7 24 28 34 44 49 54 4 5 18 34 37 40 49 50 51 56 65 68 76 30 31 34 37 42
M M M F M M F M M F F M F F F M F F M F M M M M F
hom hom hom hom hom hom hom het het het het het het het het het het het het het het het het het het
Spine BMD
Hip BMD
Forearm BMD
g/cm2
Z-score
g/cm2
Z-score
g/cm2
Z-score
1.19 2.13 2.32 2.63 2.23 2.17 1.81 0.60 0.66 1.10 1.34 1.31 1.59 1.44 1.27 1.10 1.40 1.08 1.27 1.16 1.18 1.22 1.20 1.18 1.27
7.73 9.40 11.18 14.43 10.57 10.14 7.97 1.03 1.29 0.72 2.67 2.00 5.15 4.26 2.76 0.46 4.38 2.08 2.44 3.52 0.85 1.19 0.96 0.90 2.37
1.43 2.19 2.42 2.35 2.02 2.33 1.99 0.68 0.75 1.28 1.15 1.17 1.40 1.00 1.11 1.05 1.02 0.87 1.14 0.94 1.13 1.37 1.08 1.17 1.06
NA 8.68 10.59 11.51 7.84 10.30 9.20 NA NA NA 1.51 1.13 3.71 0.73 1.64 0.53 1.23 0.49 1.62 1.80 0.70 2.54 0.37 1.12 0.96
0.56 0.92 1.02 1.04 1.13 1.00 0.84 0.32 0.34 0.63 0.61 0.82 0.66 0.58 0.62 0.71 0.64 0.55 0.71 0.47 0.69 0.81 0.68 0.70 0.68
NA 4.44 6.40 9.53 8.66 6.40 6.40 NA NA NA 1.17 2.69 2.29 1.07 1.82 0.94 2.49 1.36 1.61 0.83 0.32 2.55 0.06 0.51 2.73
M, Male; F, female; hom, homozygous; het, heterozygous; NA, not available. Abbreviations refer to family names.
a
syndactyly, a typical feature of sclerosteosis, is absent. The condition is due to a 52-kb deletion downstream of the SOST gene that is thought to down-regulate SOST expression, leading to defective sclerostin production (11, 15, 18). BMD measured in hand radiographs of four patients with van Buchem disease and nine carriers showed increased values in the patients, but not in the heterozygotes, leading to the conclusion that carriers are not affected by the genetic defect (17). This observation in carriers of van Buchem disease is different from our findings in the sclerosteosis carriers. Whether this difference is due to the methodology used to measure BMD in our study (DXA) and in the van Buchem study (radiogammometry) or to different expression of the molecular defect is currently unclear. Our results may have more general implications in understanding the role of sclerostin in bone formation and the modulation of its production and/or its activity for therapeutic purposes. Sclerostin is a secreted protein that is produced by osteocytes and inhibits bone formation (9, 10). It has been suggested that the restricted expression pattern of sclerostin and the exclusive good quality bone phenotype of patients with sclerosteosis may provide the basis for the design of therapeutics that specifically stimulate bone formation (11). One approach to achieve this is to develop antibodies capable of inhibiting the biological activity of sclerostin; this approach was shown in a preliminary report to be successful in rats (19). However, there have been concerns about such attempts to stimulate bone formation. Whyte and colleagues (20, 21), discussing the phenotypes of subjects with various bone-sclerosing disorders, including the high bone mass phenotype, suggested caution, because the use of such therapeutics may lead to unwanted skeletal
effects. These are autosomal dominant disorders, phenotypically similar to sclerosteosis, caused by gain of function mutations of the low-density lipoprotein receptor-related protein 5, which is mapped to chromosome 11q12–13 and is required for stimulation of the canonical Wnt signaling pathway in osteoblasts (22–24). This pathway is important for the bone-forming function of osteoblasts, and increased Wnt signaling resulting from lipoprotein receptor-related protein 5 mutations is responsible for the bone phenotype of these patients. Sclerostin was shown recently to antagonize Wnt signaling explaining, at least in part, its action as a negative regulator of bone formation (25, 26) (our unpublished observation). In our study, carriers of sclerosteosis with one defective copy of the SOST gene showed variable increases in bone mass without evidence of any of the skeletal complications encountered in homozygotes. These results suggest that inhibition of the production and/or activity of sclerostin can be titrated, leading to increases in bone mass without any unwanted skeletal effects. However, this hypothesis warrants additional testing in vivo. Acknowledgments We thank Sr. Lecia Bartmann for her valuable assistance with the affected families. Received June 1, 2005. Accepted September 21, 2005. Address all correspondence and requests for reprints to: Dr. Socrates E. Papapoulos, Department of Endocrinology and Metabolic Diseases, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. E-mail:
[email protected]. This work was supported by grants from Celltech, Inc., the Harry Crossley Foundation, the Mauerberger Foundation, the University of
Gardner et al. • BMD in Sclerosteosis
FIG. 2. Lumbar spine BMD in male and female homozygous and heterozygous individuals with sclerosteosis. Lines depict normal ranges. F, Homozygotes; E, heterozygotes. Cape Town Staff Research Fund, the South African Orthopedic Association (to P.B.), The Netherlands Organization for Health Research (NWO 916.046.017), and the European Commission (LSHM-CT-2003503020) (both to R.L.v.B.).
References 1. Beighton P, Durr L, Hamersma H 1976 The clinical features of sclerosteosis. A review of the manifestations in twenty-five affected individuals. Ann Intern Med 84:393–397 2. Beighton P, Hamersma H 1979 Sclerosteosis in South Africa. S Afr Med J 55:783–788 3. Beighton P 1988 Sclerosteosis. J Med Genet 25:200 –203 4. Hamersma H, Gardner J, Beighton P 2003 The natural history of sclerosteosis. Clin Genet 63:192–197 5. Beighton P, Hamersma H, Brunkow ME 2004 SOST-related sclerosting bone dysplasias. In: GeneReviews Genetics Disease Online Reviews at Gene-TestGene-Clinics. Available on-line at www.geneclinics.org 6. Balemans W, Van Den EJ, Freire Paes-Alves A, Dikkers FG, Willems PJ, Vanhoenacker F, Almeida-Melo N, Alves CF, Stratakis CA, Hill SC, Van Hul W 1999 Localization of the gene for sclerosteosis to the van Buchem diseasegene region on chromosome 17q12– q21. Am J Hum Genet 64:1661–1669 7. Balemans W, Ebeling M, Patel N, Van Hul E, Olson P, Dioszegi M, Lacza C, Wuyts W, Van Den EJ, Willems P, Paes-Alves AF, Hill S, Bueno M, Ramos FJ, Tacconi P, Dikkers FG, Stratakis C, Lindpaintner K, Vickery B, Foernzler D, Van Hul W 2001 Increased bone density in sclerosteosis is due to the deficiency of a novel secreted protein (SOST). Hum Mol Genet 10:537–543
J Clin Endocrinol Metab, December 2005, 90(12):6392– 6395
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8. Brunkow ME, Gardner JC, Van Ness J, Paeper BW, Kovacevich BR, Proll S, Skonier JE, Zhao L, Sabo PJ, Fu Y, Alisch RS, Gillett L, Colbert T, Tacconi P, Galas D, Hamersma H, Beighton P, Mulligan J 2001 Bone dysplasia sclerosteosis results from loss of the SOST gene product, a novel cystine knotcontaining protein. Am J Hum Genet 68:577–589 9. Van Bezooijen RL, Roelen BA, Visser A, Wee-Pals L, de Wilt E, Karperien M, Hamersma H, Papapoulos SE, ten Dijke P, Lo¨wik CW 2004 Sclerostin is an osteocyte-expressed negative regulator of bone formation, but not a classical BMP antagonist. J Exp Med 199:805– 814 10. Winkler DG, Sutherland MK, Geoghegan JC, Yu C, Hayes T, Skonier JE, Shpektor D, Jonas M, Kovacevich BR, Staehling-Hampton K, Appleby M, Brunkow ME, Latham JA 2003 Osteocyte control of bone formation via sclerostin, a novel BMP antagonist. EMBO J 22:6267– 6276 11. Van Bezooijen RL, ten Dijke P, Papapoulos SE, Lo¨wik CWGM 2005 SOST/ sclerostin, an osteocyte-derived negative regulator of bone formation. Cytokine Growth Factor Rev 16:319 –327 12. Hill SC, Stein SA, Dwyer A, Altman J, Dorwart R, Doppman J 1986 Cranial CT findings in sclerosteosis. Am J Neuroradiol 7:505–511 13. Stein SA, Witkop C, Hill S, Fallon MD, Viernstein L, Gucer G, McKeever P, Long D, Altman J, Miller NR, Teitelbaum SL, Schlesinger S 1983 Sclerosteosis: neurogenetic and pathophysiologic analysis of an American kinship. Neurology 33:267–277 14. Beighton P, Davidson J, Durr L, Hamersma H 1977 Sclerosteosis: an autosomal recessive disorder. Clin Genet 11:1–7 15. Staehling-Hampton K, Proll S, Paeper BW, Zhao L, Charmley P, Brown A, Gardner JC, Galas D, Schatzman RC, Beighton P, Papapoulos S, Hamersma H, Brunkow ME 2002 A 52-kb deletion in the SOST-MEOX1 intergenic region on 17q12– q21 is associated with van Buchem disease in the Dutch population. Am J Med Genet 110:144 –152 16. Van Buchem FS, Hadders HN, Ubbens R 1955 An uncommon familial systemic disease of the skeleton: hyperostosis corticalis generalisata familiaris. Acta Radiol 44:109 –120 17. Wergedal JE, Veskovic K, Hellan M, Nyght C, Balemans W, Libanati C, Vanhoenacker FM, Tan J, Baylink DJ, Van Hul W 2003 Patients with Van Buchem disease, an osteosclerotic genetic disease, have elevated bone formation markers, higher bone density, and greater derived polar moment of inertia than normal. J Clin Endocrinol Metab 88:5778 –5783 18. Balemans W, Patel N, Ebeling M, Van Hul E, Wuyts W, Lacza C, Dioszegi M, Dikkers FG, Hildering P, Willems PJ, Verheij JB, Lindpaintner K, Vickery B, Foernzler D, Van Hul W 2002 Identification of a 52 kb deletion downstream of the SOST gene in patients with van Buchem disease. J Med Genet 39:91–97 19. Warnington K, Morony S, Sarosi I, Gong J, Stephens P, Winkler DG, Sutherland MK, Latham JA, Kirby H, Moore A, Robinson M, Kostenuik PJ, Simonet S, Lacey DL, Paszty C 2005 Sclerostin antagonism in adult rodents, via monoclonal antibody mediated blockade, increases bone mineral density and implicates sclerostin as a key regulator of bone mass during adulthood. www.asbmr.org/meeting/abstracts.cfm 20. Rickels MR, Zhang X, Mumm S, Whyte MP 2005 Oropharyngeal skeletal disease accompanying high bone mass and novel LRP5 mutation. J Bone Miner Res 20:878 – 885 21. Whyte MP, Reinus WH, Mumm S 2004 High-bone-mass disease and LRP5. N Engl J Med 350:2096 –2099 22. Boyden LM, Mao J, Belsky J, Mitzner L, Farhi A, Mitnick MA, Wu D, Insogna K, Lifton RP 2002 High bone density due to a mutation in LDL-receptorrelated protein 5. N Engl J Med 346:1513–1521 23. Johnson ML, Gong G, Kimberling W, Recker SM, Kimmel DB, Recker RB 1997 Linkage of a gene causing high bone mass to human chromosome 11 (11q12–13). Am J Hum Genet 60:1326 –1332 24. Little RD, Carulli JP, Del Mastro RG, Dupuis J, Osborne M, Folz C, Manning SP, Swain PM, Zhao SC, Eustace B, Lappe MM, Spitzer L, Zweier S, Braunschweiger K, Benchekroun Y, Hu X, Adair R, Chee L, FitzGerald MG, Tulig C, Caruso A, Tzellas N, Bawa A, Franklin B, McGuire S, Nogues X, Gong G, Allen KM, Anisowicz A, Morales AJ, Lomedico PT, Recker SM, Van Eerdewegh P, Recker RR, Johnson ML 2002 A mutation in the LDL receptorrelated protein 5 gene results in the autosomal dominant high-bone-mass trait. Am J Hum Genet 70:11–19 25. Li X, Zhang Y, Kang H, Liu W, Liu P, Zhang J, Harris SE, Wu D 2005 Sclerostin binds to LRP5/6 and antagonizes canonical Wnt signaling. J Biol Chem 280: 19883–19887 26. Semenov M, Tamai K, He X 2005 SOST is a ligand for LRP5/LRP6 and a WNT signaling inhibitor. J Biol Chem 280:26770 –26775
JCEM is published monthly by The Endocrine Society (http://www.endo-society.org), the foremost professional society serving the endocrine community.