Renal osteodystrophy in children treated with 1,25-dihydroxy-cholecalciferol [1,25-(OH)2D3]. Histologic bone studies

Eleven uremic children with osteodystrophy aged 3 to 17 years were studied during administration of 1,25-(OH)2D3 for periods up to 21 months. Nine children presented with pure hyperparathyroidism, one with osteomalacia and one with mixed bone disease. Bone biopsies were performed before initiation of therapy and after 6 to 21 months of treatment following double tetracycline labeling. Skeletal lesions were improved but not cured in 5 of 9 children with hyperparathyroidism. In three instances lesions remained unchanged and worsened in one. No significant change was observed in the child with osteomalacia. Moderate improvement was noted in the patient with mixed bone disease. The propensity to develop hypercalcemia was the major factor associated with treatment failure since it precluded administration of adequate amounts of medication. Therapy with 1,25-(OH)2D3 was associated with a spectacular improvement in growth velocity in two of six children under age twelve.

Effects of phosphate and 1,25(OH)2D3 on in vitro bone collagen synthesis in the hypophosphatemic mouse

Calvarial bones from hypophosphatemic (Hyp) mice and normal littermates were cultured in a chemically defined medium to determine: (a) the effect of medium phosphate (Pi) concentration (1, 2, and 3 mM) on collagen synthesis; (b) the effect of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] (10(-12)M-10(-7)M) on collagen synthesis; and (c) whether bone responsiveness to 1,25(OH)2D3 was affected by changes in medium Pi concentration. Bone collagen synthesis was evaluated by measuring [ 3H ]hydroxyproline formation. The distribution of labeled hydroxyproline between bone explant and culture medium (total and dialyzable fraction) was studied. These experiments confirm that 1,25(OH)2D3 inhibits specifically bone collagen synthesis in vitro. We did not detect any effect of medium Pi concentration on basal collagen synthesis but were able to demonstrate that lowering medium Pi concentration increased the 1,25(OH)2D3-induced inhibition of collagen synthesis. Bones from both genotypes responded to 1,25(OH)2D3, but modulation of this response by changes in Pi concentration was altered in Hyp bone as, in contrast to normal bone, its response to 1,25(OH)2D3 was unaffected when medium Pi concentration was decreased from 3 to 2 mM. These findings support the hypothesis of an altered response of bone to 1,25(OH)2D3 in the Hyp mouse.

Congenital primary cutaneous osteoma: biochemical and histological studies

Biopsies of a cutaneous osteoma and of normal-looking skin from a 1-year-old girl were studied for histological appearance and collagen biochemistry. The mineralized tissue contained a matrix similar to bone: Only type I collagen, with a hydroxylysine content (0.48%) higher than in the skin (0.35%) and dihydroxylysinonorleucine as the major reducible crosslink. As expected, the normal skin adjacent to the lesions contained type I and type III collagen and as major crosslinks hydroxylysinonorleucine and histidinohydroxymerodesmosine. Histological studies showed the presence of woven bone with very little trabeculation. Numerous active osteoblasts were laying down a rapidly calcified non-lamellar matrix. Osteocytes and multinucleated osteoclasts were also noted. The study demonstrates the osseous nature of the lesion and suggests that an abnormal cell differentiation is associated with this form of osteoma.

Panostotic fibrous dysplasia: a congenital disorder of bone with unusual facial appearance, bone fragility, hyperphosphatasemia, and hypophosphatemia

We report a boy with unusual facial appearance, melanotic patches ("coast-of-Maine" type), myelofibrosis, recurrent femoral fractures, and widespread fibrous dysplasia of bone. Biochemical findings included raised serum alkaline phosphatase (bone isozyme) and 1,25-(OH)2 vitamin D, and low serum phosphorus levels. Elevated urinary excretion rates of total hydroxyproline, glycylproline, and gamma-carboxyglutamic acid indicated increased turnover of bone matrix. Transiliac bone biopsy showed a dearth of marrow elements, greatly increased bone turnover, and absence of normal trabecular organization. Serial radiographs showed progressive cortical thinning and loss of bony trabeculae. Calcitonin and etidronate treatments had no lasting effect on the progressive bone disease. The term "panostotic fibrous dysplasia" is suggested for this condition.

Vitamin D metabolism in preterm infants. Serial serum calcitriol values during the first four days of life

In order to evaluate after birth the changes in circulating vitamin D metabolite levels in preterm babies supplemented with vitamin D (2 100 I.U./d), the serum concentration of 25-hydroxyvitamin D [25-OHD] and 1 alpha,25-dihydroxyvitamin D [1,25(OH)2D] were measured in 22 infants (31 to 35 weeks of gestation) from birth up to 96 hours of age. Compared to cord blood levels, serum calcium decreased significantly during the first 24 hours of life (p less than 0.005) and remained low until day 4. Serum immunoreactive parathyroid hormone (iPTH) levels increased from birth to 24 hours and then plateaued. The 25-OHD levels at birth were 27.5 +/- 2.5 nmol/l and increased to 67.5 +/- 12.5 nmol/l (p less than 0.005) during the four days of the study. During the same period, the 1,25(OH)2D serum levels increased steadily from 84 less than 7 to 343 less than 105 pmol/l (p less than 0.005). At all times, there was a positive correlation between 25-OHD levels and those of 1,25(OH)2D. Our data demonstrate that in preterm infants after 31 weeks of gestation, absorption and activation of vitamin D is present as soon as 24 hours after birth and that early neonatal hypocalcemia is unlikely to be caused by an impairment of either PTH secretion or vitamin D activation.

Osteoblasts isolated from mouse calvaria initiate matrix mineralization in culture

A method is presented for isolating osteoblasts from newborn mouse calvaria without the use of digestive enzymes. The procedure is based on the ability of osteoblasts to migrate from bone onto small glass fragments (Jones, S.J., and A. Boyde, 1977, Cell Tissue Res., 184:179-193). The isolated cells were cultured for up to 14 d in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum and 50 micrograms/ml of ascorbic acid. 7-d cultures were incubated for 24 h with [3H]proline. High levels of collagen synthesis relative to total protein were found, as measured by collagenase digestion of medium and cell layer proteins. Analysis of pepsin-digested proteins from the same cultures by SDS PAGE showed that type I collagen was predominantly produced with small amounts of type III and V (alpha 1 chains) collagens. Osteoblasts grown in the presence of beta-glycerophosphate were able to initiate mineral deposition in culture. Electron microscopic analysis of the cultures revealed the presence of needle-shaped apatite-like crystals associated with collagen fibrils and vesicles in the extracellular space. Mouse skin fibroblasts cultured under identical conditions failed to initiate mineralization. Electron histochemical studies revealed the presence of alkaline phosphatase activity, associated with osteoblast membranes, matrix vesicles and on or near collagen fibrils. Thus these isolated osteoblasts retained in culture their unique property of initiating mineralization and therefore represent a model of value for studying the mineralization process in vitro.

Normal serum 25-hydroxyvitamin D levels in phenobarbital-treated toddlers

Serum 25-hydroxyvitamin D (25-OHD) levels were measured in 74 children randomly treated in a double-blind fashion with either 5 phenobarbital/kg/day or placebo after a single febrile seizure. Phenobarbital treatment for a period from 5 to 12 months had no effect on the 25-OHD levels. However, both in the phenobarbital and the placebo groups, vitamin D supplementation raised the circulating 25-OHD concentration (p less than 0.05). Whether it has a protective effect remains thus to be seen.

Control of vitamin D metabolism in preterm infants: feto-maternal relationships

To assess the relationship between maternal and fetal mineral homeostasis, serum calcium, magnesium, inorganic phosphate, parathyroid hormone, and vitamin D metabolite concentrations in venous cord sera from 15 preterm singletons and 3 twin pairs were compared with the levels found in maternal sera. Cord calcium, magnesium, and phosphorus levels were significantly higher than the respective levels in maternal samples. There was a significant relationship between the two compartments for all three analyses. Cord serum 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, and 1,25-dihydroxyvitamin D levels were significantly lower than those observed for the mothers. Association of the cord concentration with that of the mothers was observed only for the first two metabolites. There was no relationship between the maternal 1,25-dihydroxyvitamin D levels and gestational age, calcium, magnesium, inorganic phosphate, or 25-hydroxyvitamin D. Cord 1,25-dihydroxyvitamin D correlated significantly only with cord calcium levels. Immunoreactive parathyroid hormone levels were within normal limits both in cord and maternal samples. Our data suggest that after 31 weeks of gestation: (1) calcium, magnesium, and inorganic phosphate cross the placental barrier against a concentration gradient; (2) the fetus depends on the maternal supply for 25-hydroxyvitamin D and 24,25 dihydroxyvitamin D; (3) the feto-placental unit synthesizes 1,25-dihydroxyvitamin D according to fetal needs.

Histological osteomalacia due to dietary calcium deficiency in children

We performed a histomorphometric study of trabecular-bone formation and resorption in undecalcified sections of iliac crest from three children presenting with clinical, radiologic, and biochemical evidence of rickets associated with dietary calcium deficiency. All three children had severe osteomalacia documented by hyperosteoidosis and reduced static and dynamic indicators of bone mineralization. There was a reduction of the calcified bone volume associated with a decreased bone formation rate and features of increased bone resorption. Correction of dietary calcium intake in two of the patients led to normal serum and urinary calcium levels and reduced alkaline phosphatase levels. After calcium therapy, the calcified bone volume was normal and indicators of bone mineralization returned to normal. We conclude that low calcium intake in children may be associated with a histologic picture of severe osteomalacia. Our finding that adequate amounts of calcium rapidly improved bone mineralization demonstrates that calcium deficiency can cause osteomalacia in children.

Healing of bone lesions with 1,25-dihydroxyvitamin D3 in the young X-linked hypophosphatemic male mouse

The X-linked hypophosphatemic (Hyp) mouse presents with biochemical and skeletal abnormalities similar to those of human vitamin D-resistant rickets and hence is considered as a model of the human disease. In an attempt to correct osteomalacia, young (21-day-old) mutant male mice were infused continuously for 4 weeks with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3; 0.05--0.25 microgram/kg . day]. Mineral and skeletal changes were assessed by serum, urinary, and bone ash concentrations of calcium, phosphorus, and magnesium and by histomorphometric analysis of bone formation measured on histological sections of tetracycline dual labeled undecalcified caudal vertebrae. Treatment with 1,25-(OH)2D3 produced a dose-dependent elevation of serum phosphorous that could be assigned to increased intestinal phosphate absorption. Concomitantly, epiphyseal, endosteal, and periosteal bone mineralization were improved in correlation with both the dosage of 1,25-(OH)2D3 and the serum phosphorus level. Normalization of serum calcium and phosphorus but not of urinary phosphate excretion were achieved together with complete healing of bone mineralization when the highest doses of 1,25-(OH)2D3 (0.175--0.35 microgram/kg . day) were given. The data show that rickets and osteomalacia, which characterize the young Hyp mouse, can be healed by 1,25-(OH)2D3 in doses high enough to normalize serum mineral concentrations. Unlike the renal phosphate leak, the phenotypic expression of the Hyp gene pertaining to bone mineralization is then corrected by 1,25-(OH)2D3 supplementation.

Analysis of the type of collagen present in osteoarthritic human cartilage

Abnormal synthesis of type I collagen by fibrocartilage has been suggested as a mechanism involved in degenerative arthritis. Samples of normal and osteoarthritic adult femoral head cartilage were thus studied for histology and collagen composition. The electrophoretic analysis of the cyanogen bromide-derived peptides showed the sole presence of type II collagen in all normal and in all osteoarthritic samples, except those in which fibrocartilage was present. The sensitivity of the technique would not permit, however, the detection of a minute amount (less than 3%) of type I collagen in the samples. The results show that massive deposition of type I collagen occurs only when fibrocartilage is formed. It is suggested that this fibrocartilage is formed when the subchondral bone is damaged.

Bone response to phosphate and vitamin D metabolites in the hypophosphatemic male mouse

The hypophosphatemic male mouse (Hyp/y), the proposed model for human vitamin D-resistant rickets (VDRR), is characterized by chronic hypophosphatemia, dwarfism, and rachitic and osteomalacic bone lesions. We have reported that treatment of Hyp/y mice with phosphate salts (Pi) heals rickets but does not correct the defective endosteal bone mineralization. In an attempt to cure osteomalacia, mutant male animals were treated with Pi combined with 25-hydroxyvitamin D3 (25OHD3, 1 microgram/kg/day), 24,25-dihydroxyvitamin D3 [24,25(OH)2D3, 0.5 microgram/kg/day], or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3, 0.05--0.25 microgram/kg/day] infused constantly for 3 weeks. The biochemical and skeletal effects of treatment were assessed by analytical methods and bone histomorphometry. The results show that only 1,25(OH)2D3 produced a dose-dependent elevation of serum calcium and phosphorus, and greatly improved bone mineralization at doses high enough to increase serum calcium and phosphorus concentrations within or above the normal range. Better improvement of bone mineralization was obtained when Pi was combined to 1,25(OH)2D3. In conjunction with the correction of hypocalcemia, Pi + 1,25(OH)2D3 suppressed the stimulation of bone turnover induced by Pi supplementation. The results show that, as in VDRR children, 1,25(OH)2D3 produces beneficial effects on bone lesions in Hyp/y mice, mainly through enhancement of mineral availability. However, the persistence of osteomalacia despite correction of serum mineral concentrations suggests that there is a specific bone cell resistance to mineral and/or hormonal influences in Hyp/y mice.

Early oral administration of vitamin D and its metabolites in premature neonates. Effect on mineral homeostasis

For five days, three groups of six premature infants each were fed human milk and given a daily dosage of one of the following: vitamin D3 (30 micrograms), 25-OH D3 (10 micrograms) and 1,25-OH D3 (0.5 micrograms). The infants in the groups were matched for gestational age and birthweight. Administration of 25-OH De or 1,25-(OH)2 D3 did not significantly modify the course of early neonatal hypocalcemia as compared with infants receiving vitamin C3. Mean plasma Ca +/- S. D. (mg/100 ml) decreased to nadir values at 48 hr (D3: 5.7 +/-1.2; 25 OH D3: 6.8 +/- 0.9; 1.25-(OH)2 D3: 6.7 +/-1.1). A progressive increase toward normal values was seen at 120 and 168 hr in the three groups. Mean plasma immunoreactive parathyroid hormone +/- S.D. (microliters Eq/ml) followed an opposite pattern with peak values at 48 hr (D3: 231 +/- 137; 25-OH D3: 281 +/- 138; 1,25-(OH)2 D3:211 +/- 149). Mean plasma +/- S.D. 25-OH values (ng/ml) were low at 1.2 hr (8.7 +/- 4.8) n: 16) and increased significantly after 7 days of D3 (18.2 +/- 4.2 P less than 0.001) and 25-OH D3 administration (46 +/- 10.3 P less than 0.001)/Mean plasma iCT +/- S.D. (pg/ml) reached peak values at 24 hr (D3: 457 +/- 186; 25-OH D3: 415 +/- 121; 1.25-(OH)2 D3: 443 +/- 183). These data suggest that the various forms of vitamin D are well absorbed in preterm infants and that administration of vitamin D metabolites during the first days of life is not warranted for they prophylaxis of early neonatal hypocalcemia.

Bone histomorphometry in asymptomatic adults with hereditary hypophosphatemic vitamin D-resistant osteomalacia

Vitamin D-resistant rickets (VDRR) in adults is characterized by low serum phosphorus and osteomalacia. Despite the disappearance of rickets after the closure of epiphyses, some adults with VDRR present with symptomatic bone disease while other are asymptomatic. In order to test the presumption that asymptomatic adults no longer have active bone disease, we have compared bone histology in 10 symptom-free adults to 6 age-comparable symptomatic adults presenting with bone pain and persistent deformities. Both groups had similar low serum phosphorus and increased serum alkaline phosphatase values. Serum calcium, parathyroid hormone, and vitamin D metabolite concentrations were not different in the two groups. Histomorphometric study of bone formation and resorption was made on undecalcified sections of iliac crest bone biopsies obtained after in vivo single or dual tetracycline labeling. Bone histology revealed that both groups of patients had comparable osteomalacia, as evidenced by increased amount of osteoid tissue, prolonged mineralization lag time, and reduced bone formation rate. Despite the presence of osteomalacia, the trabecular calcified bone volume was within or above normal values in the two groups, implying a remodeling imbalance between the rates of bone resorption and formation. The data show that despite the absence of symptoms and the disappearance of rickets, adults with VDRR still have active bone disease characterized by moderate to severe osteomalacia. The normal to increased trabecular bone mass implies that the occurrence of painful symptoms results from factors other than trabecular osteopenia. These observations thus lead one to question the utility of active medical treatment with vitamin D and/or phosphate in asymptomatic adults with VDRR.

Vitamin D metabolism in preterm infants: serum calcitriol values during the first five days of life

To ascertain the activity of the vitamin D biosynthetic pathway, the serum concentration of 1,25-dihydroxyvitamin D (calcitriol) was measured in 16 preterm infants (32 to 37 weeks of gestation) at 1 to 2 and 120 hours of age. Half of the subjects received a daily oral supplement of 2,100 IU of vitamin D3 during the five-day study period. In the first two hours of life, all subjects were hypocalcemic (8.2 +/- 0.2 mg/dl) and 14 subjects had low concentrations of 25-hydroxyvitamin D (calcidiol, 8 +/- 1 ng/ml). The latter finding probably reflects a mild degree of vitamin D deficiency in the mothers of our subjects. Calcitriol concentrations (42 +/- 3 pg/ml) were comparable to those of older children. At 120 hours of age, the control group had no significant change in calcitriol values, whereas the group supplemented with D3 had a more than threefold increase. There was a positive correlation between the circulating concentrations of calcidiol and calcitriol over the period of the study. The data show that, after 32 weeks of gestation, renal 25-hydroxyvitamin D-1 alpha-hydroxylase activity is present, with the rate of calcitriol synthesis being apparently substrate limited. Early neonatal hypocalcemia is therefore unlikely to be caused by an impairment of vitamin D activation.

Influence of vitamin D3 status, phenobarbital, and diphenylhydantoin treatment on the plasma 25-hydroxyvitamin D3 concentrations in the rat

The plasma 25-hydroxyvitamin D3 (25(OH)D3) response to a single intraportal injection of 100 μg∙kg−1 of vitamin D3 (D3) was determined before as well as 24 and 48 h after D3 administration in male Sprague-Dawley rats following a 3-week treatment with phenobarbital (PB), diphenylhydantoin (DPH), or the combination of the two drugs during normal vitamin D status (D+) or vitamin D deficiency (D−). Before D3 injection, plasma 25(OH)D3 concentrations were not statistically affected by the anticonvulsant (ACV) drug treatment in the D+ group and were at undetectable levels in the D− group. Twenty-four hours after D3, mean plasma 25(OH)D3 concentrations in the D− rats varied between 24.4 and 76.7 ng∙mL−1 while, in the D+ animals, the mean concentrats varied between 28.3 and 50.1 ng∙mL−1. The factorial analysis of variance revealed a significant effect of the drug treatment on plasma 25(OH)D3, concentrations in all groups (p < 0.005), a nonsignificant effect of the deficiency but a statistically significant positive interaction between PB and the D− state (p < 0.001). In the subsequent 24 h, 25(OH)D3 concentrations did not change significantly in both D− and D+ controls; in ACV drug treated animals, the plasma 25(OH)D3 concentrations dropped in D− animals only, revealing a statistically significant effect of the deficiency on plasma 25(OH)D3 (p < 0.001). These observations suggest that (1) during constant intake of D3, plasma 25(OH)D3 concentrations are not affected by ACV drug treatment; (2) 24 h after an acute D3 load, the plasma 25(OH)D3 concentrations attained are (a) independent of D3 nutritional status, (b) stimulated by ACV drug treatment both in the D+ and D− states, and (c) potentiated by PB treatment during D deficiency; (3) 48 h after D3 administration, ACV drug treatment contributes, in the D− state, to accelerate the plasma 25(OH)D3 disappearance; and (4) the effects of PB on plasma 25(OH)D3 concentrations are more pronounced than those of DPH and not potentiated by the combined drug treatment.

Vitamin D dependency: replacement therapy with calcitriol?

Nine patients with vitamin D-dependency type I were studied. We observed that treatment with large doses of vitamin D altered the phenotypic expression of the disease, thus making a delayed diagnosis difficult. At the time of entry, eight children had hypocalcemia, and seven had hypophosphatemia. Elevated serum immunoreactive parathyroid hormone and low (less than 3 SD from control mean) 1 alpha,25-dihydroxyvitamin D values were constant findings, with no vitamin D deficiency. Despite the elevated serum iPTH, three children had normal urinary phosphate excretion and five had normal urinary cAMP excretion. In the five children tested before treatment, there was no significant change in renal phosphate excretion during an acute parathyroid hormone infusion, although in all a significant rise of urinary cAMP occured. Treatment with calcitriol (0.25 to 2 microgram/day) returned all the biochemical values to normal within four months. In two patients, both supplemented with vitamin D, histomorphometric analysis of iliac crest biopsies revealed severe osteomalacia. After nine and ten months of treatment with calcitriol, there was histologic evidence for improvement of bone mineralization. Since calcitriol requirements may vary during the course of treatment, careful monitoring of biochemical variables is essential.

Hypoparathyroidism during pregnancy: treatment with calcitriol

A pregnant woman suffering from idiopathic hypoparathyroidism was treated with calcitriol [0.5-2 micrograms/day 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)]. Her twin infants were delivered by cesarian section at 37 weeks of gestation. Laboratory investigations in the perinatal period disclosed: 1) normal serum calcium and phosphorus levels in the mother, 2) normal babies with no clinical or biochemical signs of hyperparathyroidism, 3) a low serum level of 25-hydroxyvitamin D despite a normal serum level of 1,25-(OH)2D in the mother, and 4) a low level of 25-hydroxyvitamin D and a high level of 1,25-(OH)2D in cord serum in both infants. It is suggested that calcitriol is an effective treatment of hypoparathyroidism during pregnancy and produces no ill effects on the baby.

Healing of rickets with phosphate supplementation in the hypophosphatemic male mouse

The hypophosphatemic male mouse, an animal model for human vitamin D-resistant rickets, is characterized by low serum phosphorus concentration due to increased urinary phosphate excretion, rickets, osteomalacia, and dwarfism. Because phosphate administration can heal rickets but not osteomalacia in the human disease, we have compared the effect of phosphate supplementation on the epiphyseal and endosteal bone mineralization in the mutant animal. Phosphate was given in drinking water for 137 d and the biochemical and bone responses were assessed by analytical and histomorphometric methods. Treatment with phosphate normalized the endochondral calcification (vertebral growthplate thickness: 83 +/- 5 SD vs. controls [+/Y] 73 +/- 8 micrometers, NS), but did not correct the endosteal bone mineralization (mineralization front: 13.6 +/- 2.7 vs. +/Y 67.1 +/- 6.9% osteoid surface, P less than 0.001, endosteal mean osteoid seam thickness: 46.4 +/- 6.1 vs. +/Y 3.3 +/- 0.3 micrometers, P less than 0.001). In addition, both osteoblastic and osteoclastic recruitment and activity were stimulated, as a result of a probable increase in parathyroid hormone secretion following the phosphate induced fall in serum calcium. Our results show that in the hypophosphatemic mouse, phosphate supplementation can heal the epiphyseal, but not the endosteal defective bone mineralization. Then, the biochemical and skeletal response to phosphate therapy appear to be similar to what we have observed in the human disease, further stressing the interest of the animal model.

X-linked hypophosphatemia: effect of calcitriol on renal handling of phosphate, serum phosphate, and bone mineralization

Eleven patients with the Mendelian phenotype of x-linked hypophosphatemia (XLH) were treated with calcitriol [1,25-(OH)2D3] and phosphate. Ten patients had received prior treatment with ergocalciferol and phosphate. Five subjects were prepubertal and six were postpubertal. Response to calcitriol was measured under nonfasting and overnight fasting protocols. Bone biopsies were obtained before and after treatment. Calcitriol (mean dose, 30 ng/kg. day) 1) raised serum phosphorus uniformly in prepubertal patients but in only two of six postpubertal subjects; 2) did not change the theoretical renal phosphate threshold in the total patient group and thus had no effect on the primary transport defect in XLH; 3) improved trabecular bone mineralization in the total patient group, as determined by bone histomorphometry. The beneficial effect on extracellular phosphorus homeostasis was attributed to improved intestinal absorption of phosphorus; improvement in bone mineralization may reflect an additional effect of 1,25-(OH)2D3 on bone itself in XLH. Mild transient hypercalcemia occurred during 0.6% of 3545 treatment days and was readily controlled by adjusting the dosage of 1,25-(OH)2D3.

Serum 1,25-dihydroxyvitamin D concentration in hypophosphatemic vitamin D-resistant rickets

Fasting serum 1 alpha, 25-dihydroxyvitamin D [1,25-(OH)2D] levels were measured in 3 groups of hypophosphatemic vitamin D-resistant rickets (VDRR) patients; those untreated; those treated with vitamin D and phosphate; and those treated with 1,25-(OH)2D3 and phosphate. In the untreated patients, the mean 1,25-(OH)2D level was higher than in our age-matched control group. Except for one at 66 pg/ml, individual values were however within normal limits. Long term vitamin D2 therapy was accompanied by a slight but significant decrease in 1,25-(OH)2D concentrations; nonetheless the levels remained within the normal range. In the third group of patients, the concentration of 1,25-(OH)2D rose to supranormal levels when sampling was done 1-3 hours after administration of the hormone, decreasing rapidly to levels below that of normal subjects when the specimens were collected 12-24 hours later. Our data show that an alteration of the vitamin D activation pathway is unlikely to be part of the pathogenic mechanism underlying the VDRR condition.

The collagen crosslinking in the hypophosphatemic male mouse

In order to evaluate the influence of bone mineralization on collagen metabolism, the bone collagen crosslinks were determined in femur diaphyses of mice with X-linked hypophosphatemia and of control littermates. No quantitative difference could be elicited between the two groups. It was also noted that in the mouse, cortical bone maturation is accompanied by a slight increase in the number of reducible crosslinks.

Histomorphometric study of bone remodeling in hypophosphatemic vitamin D-resistant rickets

Static and dynamic histomorphometric parameters were evaluated on undecalcified iliac crest bone biopsies obtained from eight children with untreated hypophosphatemic vitamin D resistant rickets (VDRR) in an attempt to evaluate whether a primary metabolic bone defect contributes to the skeletal disorder observed in that disease. When compared to normal age-matched controls the trabecular calcified bone volume was not decreased and there was no evidence of excessive osteoclastic resorption. Both trabecular and cortical bone envelopes had an excess of osteoid tissue and a decreased extent of the mineralization front. Dual tetracycline labeling revealed a decrease in the osteoblastic calcification rate and a marked prolongation of the mineralization lag time and of the formation period. In the intracortical Haversian system the birthrate of new Basic Multicellular remodeling Units (BMU) was markedly reduced, leading to a marked depression of the bone formation rate at the whole tissue level. The combination of the decreased birthrate of new BMU and the prolonged formation period appears to be characteristic of the disease. These results indicate that abnormal differentiation and function of the osteoblast contribute to the osteomalacic lesion present in VDRR. Defective mineralization and impaired osteoblastic function might be the consequence of the chronic hypophosphatemic state. However, the existence of a primary disorder of the bone cell line cannot be excluded as an explanation of the defective recruitment and function of the bone forming cells.

Induction of bone resorption by parathyroid hormone in congenital malignant osteopetrosis

A male patient, afflicted with malignant congenital osteopetrosis, was studied over a 5 year period. Hypocalcemia (less than 8 mg/dl) with lack of an appropriate increase in serum immunoreactive parathyroid hormone (iPTH) prevailed at all times. Under a calcium restricted diet, a 6-hour infusion of parathyroid extract normalized serum calcium, and increased the urinary hydroxyproline excretion suggesting that bone resorption had been induced. A second attempt to induce resorption was made by infusing a synthetic amino terminal fragment of bovine PTH over a period of 3 weeks at the dose of 1.5 units/kg/hr. This infusion evoked an increase in serum calcium (8.1 to 10.5 mg/dl), urinary calcium (0.03 to 0.65 mg/g creatinine) and urinary hydroxyproline (160 to 372 mg/g creatinine); and urinary hydroxyproline (160 to 372 mg/g creatinine); increases which were reversed by calcitonin administration. Iliac crest bone biopsies were obtained before and on the last day of the 3-week infusion. Quantitative comparison of the two specimens showed that, during PTH infusion, there was a 23% decrease in bone volume due to the increase in marrow space, a 93% increase in the number of osteoclasts and 136% increment in the osteoclastic resorption surface. Electron microscopic examination of the osteoclasts in the first tissue sample showed no evidence of ruffled borders, while in the second biopsy, numerous cytoplasmic processes indicative of resorptive activity were visible at the matrix-cell interface. It is proposed that, in our patient, the osteopetrotic phenotype is the consequence of an abnormality in the interaction between PTH and osteoclasts that may be related to the synthesis of a physiologically "defective" PTH.