GAMMA‐carboxyglutamate excretion and calcinosis in juvenile dermatomyositis

Proteins containing gamma‐carboxyglutamic acid (Gla) are present in subcutaneous calcifications of adults with dermatomyositis or scleroderma. Sixteen children with juvenile dermatomyositis, including 7 with subcutaneous calcifications, were studied to determine if abnormal synthesis or turnover of Gla‐containing proteins occurred. All study children had increased excretion of the amino acid that was greater than that of age‐and sex‐matched controls. Patients who had juvenile dermatomyositis with calcifications had a 3‐fold increase in Gla excretion, and those without calcinosis had a 2‐fold increase. Five other children with various connective tissue disorders and subcutaneous calcification had 2‐fold increased Gla excretion. Decreased excretion of this amino acid was associated with salicylate therapy (80 mg/kg/24 hours). The data suggest an abnormal turnover of Gla‐containing proteins in juvenile dermatomyositis. Metabolism of these proteins may be involved in the pathophysiology of soft‐tissue calcification in children.