Calcinosis in juvenile dermatomyositis: a possible role for the vitamin K-dependent protein matrix Gla protein.
OBJECTIVE
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.
van Summeren
M J H
MJ
Department of Pediatric Immunology, University Medical Centre Utrecht, Lundlaan 6, room KE.04.133.1, 3584 EA Utrecht, The Netherlands. m.j.h.vansummeren@umcutrecht.nl
Spliet
W G M
WG
van Royen-Kerkhof
A
A
Vermeer
C
C
Lilien
M
M
Kuis
W
W
Schurgers
L J
LJ
D000293:Adolescent; D015415:Biomarkers / Q000032:analysis / Q000378:metabolism; D002114:Calcinosis / Q000209:etiology / Q000473:pathology*; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D016022:Case-Control Studies; D002648:Child; D015331:Cohort Studies; D003882:Dermatomyositis / Q000150:complications / Q000473:pathology*; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D032342:Muscle Cells / Q000378:metabolism / Q000473:pathology; D009130:Muscle, Smooth / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D012016:Reference Values; D012680:Sensitivity and Specificity; D046509:Tissue Culture Techniques; D014812:Vitamin K / Q000494:pharmacology*; D000097568:Matrix Gla Protein
D015415:Biomarkers; D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D014812:Vitamin K; D000097568:Matrix Gla Protein