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Rheumatology Advance Access originally published online on January 29, 2008
Rheumatology 2008 47(3):267-271; doi:10.1093/rheumatology/kem360
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Calcinosis in juvenile dermatomyositis: a possible role for the vitamin K-dependent protein matrix Gla protein

M. J. H. van Summeren1, W. G. M. Spliet2, A. van Royen-Kerkhof1, C. Vermeer3, M. Lilien4, W. Kuis1 and L. J. Schurgers3

1Department of Pediatric Immunology, 2Department of Pathology, University Medical Centre Utrecht, Utrecht, 3Department of Biochemistry, University of Maastricht, Maastricht, 4Department of Pediatric Nephrology, University Medical Centre Utrecht, Utrecht, The Netherlands.

Correspondence to: M. J. H. van Summeren, Department of Pediatric Immunology, University Medical Centre Utrecht, Lundlaan 6, room KE.04.133.1, 3584 EA Utrecht, The Netherlands. E-mail: m.j.h.vansummeren{at}umcutrecht.nl


  Abstract

Objectives. The aims of the present study were to investigate whether the calcification inhibitor matrix Gla protein (MGP) is expressed in muscle biopsies of patients with juvenile dermatomyositis (JDM), and whether different forms of MGP are differentially expressed in JDM patients with and without subcutaneous calcifications.

Methods. Muscle tissue from six JDM patients (three without calcinosis, two with calcinosis and one recently diagnosed patient), four patients with muscular dystrophy, three patients with IBM and five normal histological control subjects was used for immunohistochemistry staining using novel antibodies to different conformations of MGP.

Results. In the JDM patients, all forms of MGP [non-carboxylated MGP (ucMGP), carboxylated MGP (cMGP), non-phosphorylated MGP (serMGP) and phosphorylated MGP (pserMGP)] were more intensely stained in the perifascicular compared with the central muscle fibres. In addition, these MGP species were demonstrated in the pathological muscle fibres of IBM and dystrophy patients, but hardly in normal histological muscle tissue. In JDM patients with calcifications, only pserMGP was increased compared with those without calcifications. All forms of MGP were also found in various staining intensities in the microvasculature and macrophages of normal histological and disease biopsies.

Conclusions. MGP was expressed at the site of muscle damage in JDM patients as well as in patients with muscular dystrophy and IBM. The difference in staining intensity of pserMGP appeared to distinguish between JDM patients with and without calcifications, whereas cMGP, the other functional form, was equally expressed.

KEY WORDS: Vitamin K-dependent proteins, Matrix Gla protein, Juvenile dermatomyositis, Immunohistochemistry, Muscle

Submitted 23 July 2007; revised version accepted 6 December 2007.
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