Calcif Tissue Int (1992) 51:20-23
Calcified Tissue International 9 1992 Springer-Verlag New York Inc.
Idiopathic Juvenile Osteoporosis: Evidence of Normal Osteoblast Function by 1,25-Dihydroxyvitamin D 3 Stimulation Test Silvano Berteiloni, G. I. Baroncelli, G. Di Nero, and G. Saggese Calcium Research Center, Endocrine Unit, Department of Pediatrics, University of Pisa, Pisa 1-56126, Italy Received November 4, 1991, and in revised form January 23, 1992
Summary. Idiopathic juvenile osteoporosis (IJO) is a rare form of bone demineralization that occurs during childhood. The mechanism of bone loss is unclear. Some bone hystomorphometric studies have found osteoblast failure and decreased bone formation in the affected patients whereas others have reported increased bone resorption. To elucidate this issue, we studied osteoblast function in six patients with IJO (five males, one female; aged 2.3-14.6 years) and five healthy sex- and age-matched subjects (four males, one female; aged 2.0-15.1 years) measuring serum values of osteocalcin under basal condition and during an osteoblast stimulation test performed by oral 1,25-dihydroxyvitamin D 3 [1,25(OH)2D3] administration (1.8 txg/l.73 mZ/daily). After a baseline day (day 0), all the subjects (patients and controls) received 1,25(OH)2D3 in four divided doses for 6 days (days 1-6). Fasting blood samples were obtained every morning (0800 h) for the determination of serum osteocalcin. Baseline osteocalcin levels were not significantly different between IJO and controls (13.58 --- 6.05 ng/ml versus 16.04 --- 5.09 ng/ml, respectively) even if two patients had low osteocalcin values. During 1,25(OH)2D3 administration, serum osteocalcin values significantly increased (P < 0.001) from baseline in both children with IJO and controls, reaching peak values not significantly different in the two groups. Our results do not support the hypothesis that defective osteoblast function is the primary factor of bone demineralization in IJO. Key words: Idiopathic juvenile osteoporosis - Osteoblast function - Osteocalcin - 1,25(OH)2D 3 administration.
Idiopathic juvenile osteoporosis (IJO) is a rare form of bone demineralization that occurs during childhood [1-5]. The disease shows a fairly uniform age of presentation, around pubertal growth spurt, in subjects previously h e a l t h y , and it spontaneously recover 3-5 years after diagnosis [ 1, 3]. Moreover, some instances of IJO have been reported also in the first years of life [4, 5]. The mechanism of bone loss in IJO is controversial. Some studies suggested that the disease may be due to excessive bone resorption [5-7]. However hystomorphometric studies found "osteoblastic arrest" or the presence of very few osteoblasts, suggesting that the principal cause of IJO may be the failure of bone formation due to failure of osteoblastic activity [1, 3, 8]. Osteocalcin is a unique protein osteoblast product released also in serum; measurement of serum osteocalcin lev-
Offprint requests to: S. Bertelloni
els has been found to be a sensitive biochemical marker of osteoblast function and of bone formation [9]. Osteocalcin synthesis is stimulated, in vitro and in vivo, b y 1,25dihydroxyvitamin D 3 [1,25(OH)2D3] [9-11], the renal vitamin D hormone [12]. Duda et al. [13] developed a 1,25(OH)2D3 stimulation test to assess osteoblast function in adult women with postmenopausal osteoporosis. We reasoned that such a test might provide a useful dynamic tool to investigate whether a primitive osteoblast dysfunction is the main cause of bone loss in IJO. We, therefore, conducted a 1,25(OH)zD3 stimulation test in patients with IJO.
Materials and Methods Patients
We examined five boys and one girl with IJO (Table 1). The diagnosis was based on bone pain and recurrent fractures at the metaphyses of long bones and/or at the vertebrae. All the patients had diffuse osteoporosis on radiographic study and/or significant reduction in bone mineral content (BMC) and in its normalization for bone width (BMC/BW) (single photon absorptiometry) when compared with appropriate age-sex reference data [4]. None of the patients had a history of nausea, vomiting, recurrent diarrhea, steatorrhea, immobilization, bleeding tendency, familial osteogenesis imperfecta, or other metabolic bone diseases. A detailed evaluation of diet showed an adequate intake of energy, protein, calcium, and phosphate. More extensive clinical details and follow-up of four patients have been reported elsewhere [2]. No treatment was given before the study. Five healthy, sex- and age-matched subjects (four males, one female; aged 2.0-15.1 years) were studied as controls (Table 1). Both patients and controls underwent the study protocol after informed consent from each parent; the study protocol was approved by the Ethical Committee for Investigation in Humans of our Pediatrics Department.
Study Protocol
After an overnight fast, the subjects were admitted to pediatrics to undergo the 1,25(OH)zD3 stimulation test for osteoblasts according to Duda et al. [13]. After a baseline day (day 0), the subjects (patients and controls) received oral 1,25(OH)2D3 (Rocaltrol, Roche, Milan) at physiological dosage (1.8 ~g/1.73 m2/daily) [15] in four divided doses during the following 6 days (days 1-6). Fasting state blood samples were obtained at 0800 h of each day for determination of serum osteocalcin levels. Blood and urine samples were also collected for determination of serum calcium (total and ionized), 24-hour urinary calcium excretion, and creatinine clearance at days 0, 3, and 6. During the test period, all the subjects assumed a standardized diet regarding calcium and phosphate intake; bedrest and
S. Bertelloni et al.: Osteoblast Function in IJO
21
Table 1. Osteoblast stimulation test. Clinical data in patients with IJO and in controls Patients
Age (yr) Sex Height (cm) Height centile a Weight (kg) Weight centile a Pubertal stage a Bone age (yr) b Kariotype
P-1
P-2
P-3
P-4
P-5
P-6
12.1 M 148.0
2.3 M 91.0 75b 14.0 50b G1Phl 1.7 46,XY
12.6 F 148.0 10-25b 40.2 25b B2Ph2 10.0 46,XX
9.0 M 126.0 10-25 b 25.3 25.0 b G1Phl 9.0 46,XY
14.6 M 160.0 25 b 57.5 50b G2Ph3 14.0 46,XY
11.6 M 148.2 75b 39.2 75 b G2Phl 11.0 46,XY
C-1
C-2
C-3
C-4
C-5
2.0 M 90.2 50-75 b 14.5 50-75 b G1Phl 2.0 46,XY
8.7 M 137.5 25-50 c 26.9 50c G1Phl 9.0 46,XY
11.7 F 151.0 25b 42.5 25b B2Ph2 12.0 46,XX
12.9 M 145.5 50b 35.5 50b G2Ph2 11.6 46,XY
15.1 M 166.6 25-50 b 56.3 50b G3Ph3 14.6 46,XY
50 b
44.0 75-90 b G1Phl 12.0 46,XY Controls
Age (yr) Sex Height (cm) Height centile a Weight (kg) Weight centile a Pubertal stage a Bone age (yr) b Kariotype
a According to Tanner and Whitehouse standards (Arch Dis Child 1976; 51:170-181); G, Ph, and B indicate genitalia, pubic hair, and breast, respectively b According to Greulych and Pyle method (Radiographic atlas of skeletal development of the hand and wrist. Stanford University Press, Stanford, CA)
Table 2. Osteoblast stimulation test. Biochemical data before 1,25(OH)zD 3 administration Patients Calcium Calcium+ + Osteocalcin U-calcium Ccr
mmol/L mmol/L ng/ml mg/kg/24 h ml/min/1.73 m 2
2.45 1.24 13.58 2.66 117.40
-+ -+ -+ -+ +
Controls 0.18 0.04 6.04 0.49 10.83
2.38 1.20 16.04 2.37 118.80
-+ -+ -+ -+ +
n.y. 0.11 0.04 5.08 0.30 12.95
2.40 -+ 0.30 1.20 -+ 0.10 20.80 - 8.50 a
Calcified Tissue International 9 1992 Springer-Verlag New York Inc.
Idiopathic Juvenile Osteoporosis: Evidence of Normal Osteoblast Function by 1,25-Dihydroxyvitamin D 3 Stimulation Test Silvano Berteiloni, G. I. Baroncelli, G. Di Nero, and G. Saggese Calcium Research Center, Endocrine Unit, Department of Pediatrics, University of Pisa, Pisa 1-56126, Italy Received November 4, 1991, and in revised form January 23, 1992
Summary. Idiopathic juvenile osteoporosis (IJO) is a rare form of bone demineralization that occurs during childhood. The mechanism of bone loss is unclear. Some bone hystomorphometric studies have found osteoblast failure and decreased bone formation in the affected patients whereas others have reported increased bone resorption. To elucidate this issue, we studied osteoblast function in six patients with IJO (five males, one female; aged 2.3-14.6 years) and five healthy sex- and age-matched subjects (four males, one female; aged 2.0-15.1 years) measuring serum values of osteocalcin under basal condition and during an osteoblast stimulation test performed by oral 1,25-dihydroxyvitamin D 3 [1,25(OH)2D3] administration (1.8 txg/l.73 mZ/daily). After a baseline day (day 0), all the subjects (patients and controls) received 1,25(OH)2D3 in four divided doses for 6 days (days 1-6). Fasting blood samples were obtained every morning (0800 h) for the determination of serum osteocalcin. Baseline osteocalcin levels were not significantly different between IJO and controls (13.58 --- 6.05 ng/ml versus 16.04 --- 5.09 ng/ml, respectively) even if two patients had low osteocalcin values. During 1,25(OH)2D3 administration, serum osteocalcin values significantly increased (P < 0.001) from baseline in both children with IJO and controls, reaching peak values not significantly different in the two groups. Our results do not support the hypothesis that defective osteoblast function is the primary factor of bone demineralization in IJO. Key words: Idiopathic juvenile osteoporosis - Osteoblast function - Osteocalcin - 1,25(OH)2D 3 administration.
Idiopathic juvenile osteoporosis (IJO) is a rare form of bone demineralization that occurs during childhood [1-5]. The disease shows a fairly uniform age of presentation, around pubertal growth spurt, in subjects previously h e a l t h y , and it spontaneously recover 3-5 years after diagnosis [ 1, 3]. Moreover, some instances of IJO have been reported also in the first years of life [4, 5]. The mechanism of bone loss in IJO is controversial. Some studies suggested that the disease may be due to excessive bone resorption [5-7]. However hystomorphometric studies found "osteoblastic arrest" or the presence of very few osteoblasts, suggesting that the principal cause of IJO may be the failure of bone formation due to failure of osteoblastic activity [1, 3, 8]. Osteocalcin is a unique protein osteoblast product released also in serum; measurement of serum osteocalcin lev-
Offprint requests to: S. Bertelloni
els has been found to be a sensitive biochemical marker of osteoblast function and of bone formation [9]. Osteocalcin synthesis is stimulated, in vitro and in vivo, b y 1,25dihydroxyvitamin D 3 [1,25(OH)2D3] [9-11], the renal vitamin D hormone [12]. Duda et al. [13] developed a 1,25(OH)2D3 stimulation test to assess osteoblast function in adult women with postmenopausal osteoporosis. We reasoned that such a test might provide a useful dynamic tool to investigate whether a primitive osteoblast dysfunction is the main cause of bone loss in IJO. We, therefore, conducted a 1,25(OH)zD3 stimulation test in patients with IJO.
Materials and Methods Patients
We examined five boys and one girl with IJO (Table 1). The diagnosis was based on bone pain and recurrent fractures at the metaphyses of long bones and/or at the vertebrae. All the patients had diffuse osteoporosis on radiographic study and/or significant reduction in bone mineral content (BMC) and in its normalization for bone width (BMC/BW) (single photon absorptiometry) when compared with appropriate age-sex reference data [4]. None of the patients had a history of nausea, vomiting, recurrent diarrhea, steatorrhea, immobilization, bleeding tendency, familial osteogenesis imperfecta, or other metabolic bone diseases. A detailed evaluation of diet showed an adequate intake of energy, protein, calcium, and phosphate. More extensive clinical details and follow-up of four patients have been reported elsewhere [2]. No treatment was given before the study. Five healthy, sex- and age-matched subjects (four males, one female; aged 2.0-15.1 years) were studied as controls (Table 1). Both patients and controls underwent the study protocol after informed consent from each parent; the study protocol was approved by the Ethical Committee for Investigation in Humans of our Pediatrics Department.
Study Protocol
After an overnight fast, the subjects were admitted to pediatrics to undergo the 1,25(OH)zD3 stimulation test for osteoblasts according to Duda et al. [13]. After a baseline day (day 0), the subjects (patients and controls) received oral 1,25(OH)2D3 (Rocaltrol, Roche, Milan) at physiological dosage (1.8 ~g/1.73 m2/daily) [15] in four divided doses during the following 6 days (days 1-6). Fasting state blood samples were obtained at 0800 h of each day for determination of serum osteocalcin levels. Blood and urine samples were also collected for determination of serum calcium (total and ionized), 24-hour urinary calcium excretion, and creatinine clearance at days 0, 3, and 6. During the test period, all the subjects assumed a standardized diet regarding calcium and phosphate intake; bedrest and
S. Bertelloni et al.: Osteoblast Function in IJO
21
Table 1. Osteoblast stimulation test. Clinical data in patients with IJO and in controls Patients
Age (yr) Sex Height (cm) Height centile a Weight (kg) Weight centile a Pubertal stage a Bone age (yr) b Kariotype
P-1
P-2
P-3
P-4
P-5
P-6
12.1 M 148.0
2.3 M 91.0 75b 14.0 50b G1Phl 1.7 46,XY
12.6 F 148.0 10-25b 40.2 25b B2Ph2 10.0 46,XX
9.0 M 126.0 10-25 b 25.3 25.0 b G1Phl 9.0 46,XY
14.6 M 160.0 25 b 57.5 50b G2Ph3 14.0 46,XY
11.6 M 148.2 75b 39.2 75 b G2Phl 11.0 46,XY
C-1
C-2
C-3
C-4
C-5
2.0 M 90.2 50-75 b 14.5 50-75 b G1Phl 2.0 46,XY
8.7 M 137.5 25-50 c 26.9 50c G1Phl 9.0 46,XY
11.7 F 151.0 25b 42.5 25b B2Ph2 12.0 46,XX
12.9 M 145.5 50b 35.5 50b G2Ph2 11.6 46,XY
15.1 M 166.6 25-50 b 56.3 50b G3Ph3 14.6 46,XY
50 b
44.0 75-90 b G1Phl 12.0 46,XY Controls
Age (yr) Sex Height (cm) Height centile a Weight (kg) Weight centile a Pubertal stage a Bone age (yr) b Kariotype
a According to Tanner and Whitehouse standards (Arch Dis Child 1976; 51:170-181); G, Ph, and B indicate genitalia, pubic hair, and breast, respectively b According to Greulych and Pyle method (Radiographic atlas of skeletal development of the hand and wrist. Stanford University Press, Stanford, CA)
Table 2. Osteoblast stimulation test. Biochemical data before 1,25(OH)zD 3 administration Patients Calcium Calcium+ + Osteocalcin U-calcium Ccr
mmol/L mmol/L ng/ml mg/kg/24 h ml/min/1.73 m 2
2.45 1.24 13.58 2.66 117.40
-+ -+ -+ -+ +
Controls 0.18 0.04 6.04 0.49 10.83
2.38 1.20 16.04 2.37 118.80
-+ -+ -+ -+ +
n.y. 0.11 0.04 5.08 0.30 12.95
2.40 -+ 0.30 1.20 -+ 0.10 20.80 - 8.50 a
