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A B STR A C T The inorganic constituents and crystalline features of extraosseous calcium-phosphate deposits obtained from dialyzed uremic and hypercalcemic patients were studied. Visceral calcification (heart, lung, and kidney) in hypercalcemic patients exhibited either an amorphous or apatitic X-ray diffraction pattern. Uremic visceral calcification consistently gave an amorphous diffraction pattern. Although the calcium content of uremic and hypercalcemic visceral deposits was similar, other inorganic constituents were different. The mean pyrophosphate was 11±11.8 and magnesium 4.91±3.86 mg/g in the uremic group as compared to 0.92+0.24 and 1.36±1.26 mg/g in the hypercalcemic group (P < 0.025).After incineration hypercalcemic visceral deposits having an amorphous diffraction pattern were found to generate pyrophosphate supporting the presence of brushite in these deposits. The small amount of pyrophosphate in apatitic deposits from both uremic and hypercalcemic patients actually decreased after incineration and the pyrophosphate content of uremic visceral deposits was unchanged by incineration.It is concluded that in hypercalcemic patients the initial visceral deposit is brushite which is subsequently transformed to apatite. Arterial and tumoral calciumphosphate deposits in uremic patients were also apatite. exhibited an amorphous X-ray diffraction pattern (6). It has previously been felt that the initial extraosseous calcium-phosphate deposit is brushite (CaHPO4 2H20).Since brushite is stable at a pH of 6.2 but is rapidly transformed to apatite at a pH of 6.9 or higher, it has been stated that apatite [Calo(PO4)e8 (OH)2] is the only solid phase of calcium and phosphate that can form under physiological conditions (7). This would suggest that an inhibitor or stabilizer such as pyrophosphate (P207) 1 is present in uremic visceral calcification which prevents the transformation of these deposits to apatite.The present study was carried out to fully characterize the inorganic constituents of uremic visceral, tumoral, and arterial calcification. To determine if the crystalline characteristics of visceral calcification are primarily determined by the matrix within which it is formed, visceral calcification obtained from hypercalcemic patients was also studied to compare with the uremic deposits. METHODSTissues (heart, lung, kidney, skeletal muscle, dura, arterial, and periarticular deposits) were obtained from 11 dialyzed uremic patients previously shown to have calcifications and 3 patients who had hypercalcemia. The etiology of the hypercalcemia was different in all of the latter three patients. Two patients had acute hypercalcemia shortly before death which was secondary to multiple myeloma in one and rhabdomyolysis in the second. The third patient had long-standing undiagnosed hyperparathyroidism. At time of death these patients had normal or only moderately reduced renal function. Tissues for comparison were obtained from two control subjects who had experienced sudden death and three dialyzed uremic patients...

Platelet function and serum pyrophosphate (PPi) levels were measured in 15 osteogenesis imperfecta (OI) patients and their parents. The bleeding time was abnormal in five of the subjects. Platelet adhesion to glass was occasionally abnormal (9 of 30 subjects). Platelet factor 3 (PF3) release was impaired in all patients except one and in one or both parents. Platelet aggregation to ADP was abnormal in most of the subjects. Aggregation to collagen was also frequently defective. Thrombin-induced platelet aggregation was always normal. Serum PPi levels were elevated in 62.5% of the subjects. The increased level of PPi was occasionally related to the defect in release of PF3; however, addition of PPi to normal platelet-rich plasma (PRP) did not alter the PF3 release or ADP aggregation. Thrombin-clotted PRP contributed to the elevated PPi but no more in the subjects than in the controls. Presumed carriers of the gene for OI may have defective platelet function and elevated serum PPi, even though no obvious signs of the disease are apparent.

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