Parathyroid function in different stages of vitamin D deficiency rickets

Characteristics of vitamin D deficiency in early infancy

Purpose: Vitamin D deficiency is a health problem in developing countries. This study aims to investigate the characteristics of children with vitamin D deficiency in early infancy. Materials and Methods: Hundred and forty infants with vitamin D deficiency (mean age:3.5 ± 1.7 [0-6] months) and a control group of 200 healthy infants (mean age: 3.4 ± 1.7 [0-6] months) were included in the study. Serum calcium, phosphorus, alkaline phosphatase, parathyroid hormone (PTH), and 25-hydroxyvitamin D (25(OH)D) levels were measured in the patient, control groups, and the mothers of the patients. In 38 patients, radiological findings were evaluated with knee and wrist radiographs. Thacher Rickets Severity Scoring (RSS) system was used for radiological evaluation of rickets severity. Results: The most common (42%) complaints were respiratory symptoms, including cough, respiratory distress, and wheezing. The most common finding of physical examination was the rachitic rosary. Serum calcium (Ca++), alkaline phosphatase (ALP), 25(OH) vitamin D, and parathormone (PTH) levels were significantly different in the patient and the control groups. The mean Thacher radiological score of 38 patients was 3.1 ± 2.1 (0-8) points. The mother's dressing style of covering up the whole body, i.e., veiling, increased the infant's risk of vitamin D deficiency by 17.5 times. Conclusion: Subtle clinical, laboratory, and radiological findings of vitamin D deficiency are detected in early infancy. Vitamin D deficiency should be considered primarily in infants with hypocalcemia whose mothers are less frequently exposed to sunlight due to geographical conditions and their preferred or imposed lifestyle.

Relation between circulating levels of 25(OH) vitamin D and parathyroid hormone in chronic kidney disease: quest for a threshold

CONTEXT

Vitamin D deficiency is common in patients with chronic kidney disease (CKD). Current guidelines recommend treatment strategies in these patients similar to those for the general population, but the vitamin D nutritional status sufficient to prevent PTH levels from increasing in CKD is unknown. OBJECTIVE, MAIN OUTCOME MEASURE: Our aim was to study the relation between circulating PTH and 25(OH)D levels and to search for a 25(OH)D threshold associated with a significant PTH increase.

DESIGN, SETTING, AND PATIENTS

In the hospital-referred NephroTest cohort study, we measured 25(OH)D, PTH, and glomerular filtration rate (mGFR) by ⁵¹Cr-EDTA renal clearance in 929 adult patients with nondialysis CKD stages 1 to 5 and no vitamin D supplementation. Patients' mean age was 60.1 ± 14.7 years; 71% were men, and 9% were black. Their median mGFR was 37.8 mL/min/1.73 m².

RESULTS

We found a 25(OH)D threshold of 8 ng/mL with an upper limit of 20 ng/mL (95% confidence interval) by linear piecewise regression modeling of log-PTH for 25(OH)D adjusted for mGFR, age, race, and ionized calcium level. The smoothed curve confirmed that PTH concentration rose steeply when circulating 25(OH)D levels fell to less than 20 ng/mL.

CONCLUSIONS

Spontaneous 25(OH)D levels greater than 20 ng/mL seem sufficient to control serum PTH in CKD patients. This result reinforces guidelines to supplement vitamin D only if less than 30 ng/mL.

Vitamin D deficiency in two young adults with biochemical findings resembling pseudohypoparathyroidism type I and type II

We report two patients with vitamin D deficiency due to unbalanced diet. The patients initially presented with severe hypocalcemia, normophosphatemia and markedly elevated serum PTH levels. Although nutritional vitamin D deficiency was suspected from their history of gastrointestinal problems and dietary restriction, we conducted Ellsworth- Howard test to exclude the possibility of pseudohypoparathyroidism (PHP). Both patients showed no incremental response of urinary phosphate excretion. However, the urinary cAMP response to exogenous PTH was different between the two. Case 1 showed a blunted response (5-fold and 1.54 micro mol/h increase) and case 2 showed a normal response (39-fold and 3.04 micro mol/h increase). According to the criteria of Ellsworth-Howard test, the data of case 1 was compatible with PHP type I, and of case 2 with PHP type II. The final diagnosis of vitamin D deficiency was established in both patients based on very low serum 25-hydroxyvitamin D levels (less than 5 ng/mL) and the effect of treatment. After calcium supplementation with or without vitamin D, their biochemical abnormalities disappeared. They maintained normocalcemia without medication after correction of their unbalanced diet. The present study indicated that patients with vitamin D deficiency occasionally showed biochemical findings suggestive of PHP and that such patients could exhibit not only PHP type II pattern of response to exogenous PTH but also of type I pattern. Thus our clinical observation suggests the complexity of PTH resistance in vitamin D deficiency and underscores the importance of diet to prevent the disorder.

Vitamin D deficiency in breastfed infants in Iowa

OBJECTIVE

The purpose of this work was to assess the vitamin D status of breastfed infants living in Iowa (latitude: 41 degrees N).

METHODS

Blood samples and dietary records from 84 breastfed infants participating in another study were used for a survey of vitamin D status at 280 days of age. The vitamin D status of those (35 infants) who did not receive preformed vitamin D at 280 days of age (unsupplemented infants) was assessed longitudinally between 112 days and 15 months of age. Plasma 25-hydroxyvitamin D and, in most cases, parathyroid hormone and alkaline phosphatase were determined.

RESULTS

At 280 days of age, 10% of breastfed infants were vitamin D deficient (25-hydroxyvitamin D < 11 ng/mL). Deficiency was significantly more prevalent among dark-skinned infants and during winter and occurred exclusively in unsupplemented infants. During winter, 78% of unsupplemented infants were vitamin D deficient. During summer, only 1 infant who had dark skin pigmentation was vitamin D deficient. Longitudinal assessment of unsupplemented infants similarly showed that the majority of breastfed infants were vitamin D deficient during winter. Severe deficiency (25-hydroxyvitamin D < 5 ng/mL) was common and was accompanied by elevation of parathyroid hormone and alkaline phosphatase. The prevalence of vitamin D deficiency decreased with age but was still 12% at 15 months of age if no preformed vitamin D was received.

CONCLUSIONS

Vitamin D deficiency, including severe deficiency, was common among breastfed infants in Iowa who did not receive preformed vitamin D. Deficiency occurred mostly during winter but was not completely absent during summer. It affected infants with light as well as dark skin pigmentation. Consumption of preformed vitamin D from vitamin supplements or formula is effective in preventing vitamin D deficiency. Vitamin D supplementation should be provided to all breastfed infants.

Limited availability of nutritional vitamin D causing inappropriate treatment of vitamin D deficiency rickets with a response resembling pseudohypoparathyroidism type II in a Japanese patient

Vitamin D deficiency rickets occasionally resembles pseudohypoparathyroidism type II (PHP type II) with respect to the response to exogenous PTH in the presence of hypocalcemia. We encountered a Japanese patient with stage 2 vitamin D deficiency rickets, who had increased urinary cAMP excretion and no response of urinary phosphate or N-acetyl-beta-D-glucosaminidase excretion to exogenous PTH under normocalcemic and normophosphatemic conditions, after treatment with 1,25(OH)2 vitamin D3. This case shows that it is possible for a response mimicking that of PHP type II to occur when the serum calcidiol level is low due to causes other than hypocalcemia and secondary hyperparathyroidism. When the serum calcidiol level is low, the appropriate treatment should be cholecalciferol or ergocalciferol. However, because neither is commercially available as a useful formulation in Japan, physicians are forced to inappropriately use calcitriol or analogs.

Determination of 25-Hydroxyvitamin D in Human Plasma Using High-Performance Liquid Chromatography−Tandem Mass Spectrometry

We report here the development of a precise and sensitive method to determine 25-hydroxyvitamin D (25-OH-D(2)/ -D(3)) in human plasma using high-performance liquid chromatography-tandem mass-mass spectrometry with atmospheric pressure chemical ionization (LC-APCI-MS/MS). The method involves the use of deuterated 25-OH-D(3) as an internal standard compound for 25-OH-D(2)/-D(3), which was synthesized in our laboratory, and the selection of a precursor and product ion with a MS/MS multiple reaction monitoring method. The average intraassay and interassay variation values (relative standard deviation) were 5.7 and 2.5%, respectively, for 25-OH-D(3) and 4.5 and 5.1%, respectively, for 25-OH-D(2). The average spiked recoveries from authentic compounds added to normal human plasma samples for 25-OH-D(3) and 25-OH-D(2) were 103.8 and 98.8%, respectively. Mean plasma concentrations of 25-OH-D(3) and 25-OH-D(2) in healthy subjects were 20.5 and 0.4 ng/mL, respectively. We conclude that this novel LC-APCI-MS/MS method would be useful for the evaluation of the vitamin D status in postmenopausal women and elderly subjects and provide useful information in the diagnosis of vitamin D insufficiency/deficiency, as well as for the treatment and prevention of osteoporosis with vitamin D.

Vitamin D deficiency in early infancy

We analyzed the characteristics of young infants diagnosed with vitamin D deficiency in early infancy at 2 medical centers in Turkey. In this retrospective, cross-sectional study, the clinical, biochemical, and radiographic findings of infants who were diagnosed with vitamin D deficiency at <3 mo of age between May 2001 and May 2003 were reviewed. A total of 42 infants (27 boys and 15 girls) were diagnosed with vitamin D deficiency in the first 3 mo of life during this 2-y period. The age of infants at diagnosis was 60 +/- 19 d (range 32-112 d). The majority (78.7%) presented with seizures. No skeletal deformities were detected clinically, and radiological findings were subtle. All infants had low serum calcium levels but serum phosphorous levels varied. Eight infants (19.0%) had low, 19 (45.3%) had normal, and 15 (35.7%) had elevated serum phosphorous levels. Serum 25-hydroxyvitamin D levels in those measured (29 infants and 15 mothers) were <37.5 nmol/L. Most infants (83%) were exclusively breast-fed without supplemental vitamin D, and none of the mothers were supplemented with vitamin D during pregnancy. All mothers had limited sunlight exposure and 33 of 42 mothers (78.6%) wore concealing clothing. The majority of young infants diagnosed with vitamin D deficiency present with seizures, have low dietary vitamin D intake, and mothers with poor vitamin D reserves. Evaluation of vitamin D status should be included into the workup of hypocalcemia in early infancy. Prevention of deficiency by supplementing pregnant women and infants who are exclusively breast-fed is essential.

Stage I vitamin D-deficiency rickets mimicking pseudohypoparathyroidism type II

The clinical presentation and biochemical features of stage I vitamin D-deficiency rickets (VDR) and pseudohypoparathyroidism (PHP) type II are quite similar. These 2 entities have therefore often been mistaken for one another. We report our experience with 2 cases of stage I VDR that were originally diagnosed as PHP type II. The report provides an insight into the pathophysiology of VDR and PHP and thus allows for better differentiation between the 2 disease entities. It has become essential for pediatricians to recognize VDR owing to its resurgence in developed countries.

Pathophysiology of calcium metabolism in children with vitamin D-deficiency rickets

OBJECTIVE

To improve understanding of the biochemical events in vitamin D-deficiency rickets (VDR).

METHODS

We investigated 51 untreated patients, 2 to 36 months of age, during three stages of VDR. Nineteen of these patients were also studied during therapy with 5000 to 10,000 U vitamin D3 (cholecalciferol) and 0.5 to 1 gm calcium. Together with calcium and inorganic phosphate in serum and urine, we measured (1) parathyroid hormone (PTH) secretion (intact serum PTH) and action on the kidney (urinary adenosine 3',5'-cyclic monophosphate (cAMP)/creatinine ratio; (2) serum alkaline phosphatase level; (3) urinary hydroxyproline/creatinine ratio; and (4) serum 1,25-dihydroxyvitamin D (1,25(OH)2D) level.

RESULTS

The untreated patients had secondary hyperparathyroidism (high serum PTH and urinary cAMP/creatinine ratio), low calcium and phosphate concentrations in serum, and increased bone turnover (elevated serum alkaline phosphatase and OHP/creatinine ratio), whereas serum 1,25(OH)2D was low, normal, or even slightly elevated. Serum calcium level was positively correlated to serum 1,25(OH)2D and to OHP/creatinine ratio, indicating that normocalcemia in untreated rickets (stage 2) is at least partially maintained by 1,25(OH)2D-induced calcium mobilization from bone. There was no correlation between serum calcium and serum PTH, or between serum PTH and urinary cAMP/creatinine ratio or serum phosphate, indicating disturbed regulation and action of PTH. During vitamin D treatment, serum 1,25(OH)2D values increased to supranormal concentrations in association with the restoration of the physiologic relationship of PTH to serum calcium and phosphate concentrations and urinary cAMP/creatinine ratio.

CONCLUSION

Circulating 1,25(OH)2D has an important role in the pathophysiology of VDR before and during treatment, mainly by influencing the bone and kidney response to endogenous PTH.

Alteration in osteoblast activity and nutritional vitamin-D deficiency in non-hypercalcemic malignancy

The biochemical parameters of bone mineral metabolism in patients with nonhypercalcemic malignancy have not been extensively investigated. Therefore, a group of 29 such patients with different types of malignancy was studied. Ten patients received corticosteroids. In the entire group, serum ionized calcium (Ca2+), bone gla protein (BGP), 25-hydroxyvitamin D (25OHD), and 1,25-dihydroxyvitamin D (1,25(OH)2D) were all lower than in age-matched controls, and carboxy-terminal parathyroid hormone (CPTH) was higher. Although both corticosteroid- and noncorticosteroid-treated patients had decreased BGP values, the corticosteroid-treated patients had lower BGP levels than those not on steroids (4.24 +/- 0.70 SE vs. 11.50 +/- 2.20 ng/ml; P less than 0.005). Patients on corticosteroids had lower 1,25(OH)2D values than controls (18.81 +/- 2.71 vs. 27.83 +/- 1.17 pg/ml; P less than 0.01), whereas those not on corticosteroids had normal 1,25(OH)2D values. These results suggest that patients with nonhypercalcemic malignancy have nutritional vitamin-D deficiency and secondary hyperparathyroidism with perhaps corticosteroid-induced suppression of serum 1,25(OH)2D and BGP. The decreased levels of serum BGP in the nonsteroid-treated patients suggest, in addition, a defect in osteoblast function.

Endocrine control and disturbances of calcium and phosphate metabolism in children

Most disorders of extracellular calcium and phosphate metabolism in childhood can be attributed to primary increased or decreased secretion/action of 1,25-dihydroxyvitamin D3 and parathyroid hormone or primary increased or decreased urinary excretion of phosphate and calcium. Based on this pathogenetic classification the most important diseases related to calcium and phosphate metabolism will be discussed.

Parathyroid hormone, calcitonin and vitamin D metabolites in beta-thalassaemia major

Serum calcium (Ca), phosphorus (P), alkaline phosphatase (Al-P), parathyroid hormone (PTH), calcitonin (CT), 25-hydroxyvitamin D3 (25OHD3), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) levels and urinary excretion of Ca, P, hydroxyproline (OH-P) and cyclic AMP (cAMP) were determined in summer and in winter in 13 thalassaemic children (7 aged 3-5 years-group 1-; and 6 aged 10-13 years-group 2-), who had never taken vitamin D supplements or therapy, and in two groups of 14 controls of the same age. In thalassaemics of group 1 only serum Al-P levels and OH-P urinary excretion were higher than in controls (P less than 0.01). In thalassaemics of group 2 Ca (P less than 0.05), P (P less than 0.05), PTH (P less than 0.001), CT (P less than 0.001), 25OHD3 (P less than 0.05), 1,25(OH)2D3 (P less than 0.001) levels and cAMP urinary excretion (P less than 0.001) were lower, whereas Al-P (P less than 0.001) and CT (P less than 0.001) levels and urinary excretion of P (P less than 0.05) and of OH-P (P less than 0.001) were higher than in controls, both in summer and in winter. Advancing age induces in thalassaemic patients a decrease in PTH secretion and a consequent deficit in synthesis of 1,25(OH)2D3 that may explain some aspects of bone changes, which CT hypersecretion may tend to counteract.