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

Vitamin D Binding Protein (DBP), Free Calcidiol, and Total Calcitriol in Adults from Northern Greece

Background

An ongoing debate has been raised on whether is better to use total or free calcidiol as a screening test in the population.

Methods

In winter and summer, free calcidiol, total calcitriol, and vitamin D binding protein (DBP) concentrations were determined by immunoenzymatic assays in 326 adults (161 males, 165 females). These included 99 osteoporotic patients, 53 type 1 and 51 type 2 diabetics, and 123 athletic healthy persons, all from northern Greece.

Results

In the whole sample, free calcidiol mean concentrations differed significantly (p < 0.001) between males (5.53 pg/ml) and females (4.68 pg/ml). Free calcidiol was significantly greater in the athletic healthy group (6.02 pg/ml) than in the three patient groups, and lowest in the osteoporosis group (3.69 pg/ml). Total calcitriol mean concentration did not differ significantly between genders in the whole sample (p = 0.896) or in the study groups, except for type 2 diabetics (males 38.33 pg/ml, females 54.52 pg/ml, p = 0.001). It was significantly less in the osteoporotics (34.61 pg/ml) than in the athletic healthy group (41.65 pg/ml, p = 0.037) and type 1 diabetics (43.73 pg/ml, p = 0.030), whereas it did not differ significantly between the other study groups. The DBP mean concentrations were not significantly different between genders in the whole sample and the study groups nor among the study groups (p = 0.467).

Conclusion

Comparisons with our previously reported results of total calcidiol suggest the measurement of free calcidiol offers nothing more than that, and total calcitriol is not a sensitive measure for assessing vitamin D status.

25(OH)Vitamin D Deficiency and Calcifediol Treatment in Pediatrics

Vitamin D is essential for the normal mineralization of bones during childhood. Although diet and adequate sun exposure should provide enough of this nutrient, there is a high prevalence of vitamin D deficiency rickets worldwide. Children with certain conditions that lead to decreased vitamin D production and/or absorption are at the greatest risk of nutritional rickets. In addition, several rare genetic alterations are also associated with severe forms of vitamin-D-resistant or -dependent rickets. Although vitamin D3 is the threshold nutrient for the vitamin D endocrine system (VDES), direct measurement of circulating vitamin D3 itself is not a good marker of the nutritional status of the system. Calcifediol (or 25(OH)D) serum levels are used to assess VDES status. While there is no clear consensus among the different scientific associations on calcifediol status, many clinical trials have demonstrated the benefit of ensuring normal 25(OH)D serum levels and calcium intake for the prevention or treatment of nutritional rickets in childhood. Therefore, during the first year of life, infants should receive vitamin D treatment with at least 400 IU/day. In addition, a diet should ensure a normal calcium intake. Healthy lifestyle habits to prevent vitamin D deficiency should be encouraged during childhood. In children who develop clinical signs of rickets, adequate treatment with vitamin D and calcium should be guaranteed. Children with additional risk factors for 25(OH)D deficiency and nutritional rickets should be assessed periodically and treated promptly to prevent further bone damage.

Rickets guidance: part II-management

Here, we discuss the management of different forms of rickets, including new therapeutic approaches based on recent guidelines. Management includes close monitoring of growth, the degree of leg bowing, bone pain, serum phosphate, calcium, alkaline phosphatase as a surrogate marker of osteoblast activity and thus degree of rickets, parathyroid hormone, 25-hydroxyvitamin D₃, and calciuria. An adequate calcium intake and normal 25-hydroxyvitamin D₃ levels should be assured in all patients. Children with calcipenic rickets require the supplementation or pharmacological treatment with native or active vitamin D depending on the underlying pathophysiology. Treatment of phosphopenic rickets depends on the underlying pathophysiology. Fibroblast-growth factor 23 (FGF23)-associated hypophosphatemic rickets was historically treated with frequent doses of oral phosphate salts in combination with active vitamin D, whereas tumor-induced osteomalacia (TIO) should primarily undergo tumor resection, if possible. Burosumab, a fully humanized FGF23-antibody, was recently approved for treatment of X-linked hypophosphatemia (XLH) and TIO and shown to be superior for treatment of XLH compared to conventional treatment. Forms of hypophosphatemic rickets independent of FGF23 due to genetic defects of renal tubular phosphate reabsorption are treated with oral phosphate only, since they are associated with excessive 1,25-dihydroxyvitamin D production. Finally, forms of hypophosphatemic rickets caused by Fanconi syndrome, such as nephropathic cystinosis and Dent disease require disease-specific treatment in addition to phosphate supplements and active vitamin D. Adjustment of medication should be done with consideration of treatment-associated side effects, including diarrhea, gastrointestinal discomfort, hypercalciuria, secondary hyperparathyroidism, and development of nephrocalcinosis or nephrolithiasis.

Global consensus on nutritional rickets: Implications for Australia

In 2016, a global consensus on the prevention, diagnosis and management of nutritional rickets was published. The bone and mineral working group of the Australasian Paediatric Endocrine Group provides a summary and highlights differences to previous Australian and New Zealand (ANZ) guidelines on vitamin D deficiency and their implications for clinicians. Key points are: (i) The International Consensus document is focused on nutritional rickets, whereas the ANZ guidelines were focused on vitamin D deficiency. (ii) Definitions for the interpretation of 25-hydroxy vitamin D (25OHD) levels do not differ between statements. (iii) The global consensus recommends that routine 25OHD screening should not be performed in healthy children and recommendations for vitamin D supplementation are not based solely on 25OHD levels. The Australasian Paediatric Endocrine Group bone and mineral working group supports that screening for vitamin D deficiency should be restricted to populations at risk. (iv) Recommendations from the global consensus for vitamin D dosages for the therapy of nutritional rickets (diagnosed based on history, physical examination, biochemical testing and a confirmation by X-rays) are higher than in ANZ publications. (v) The global consensus recommends the implementation of public health strategies such as universal supplementation with vitamin D from birth to 1 year of age and food fortification. We conclude that updated global recommendations for therapy of nutritional rickets complement previously published position statements for Australia and New Zealand. Screening, management and the implementation of public health strategies need to be further explored for Australia.

Nutritional rickets in Taiwanese children: Experiences at a single center

BACKGROUND/PURPOSE

The number of children with nutritional rickets in Taiwan has increased over the last decade. The aim of this study was to present our experiences in the management of patients with this condition.

PATIENTS AND METHODS

From 2011 to 2016, 10 children (3 boys and 7 girls) with nutritional rickets were enrolled in this study. Their clinical and biochemical data were analyzed.

RESULTS

The median age of the 10 patients was 21 months (range, 12-25 months). The predisposing factors included exclusive breastfeeding, dietary restriction, and limited outdoor activities. The most common presentations were unsteady gait and bowlegs, and two patients had hypocalcemic seizures. All patients had elevated alkaline phosphatase levels (median, 1008 U/L; range, 484-2051 U/L), elevated serum intact parathyroid hormone levels (median, 333.8 pg/mL; range, 130-817 pg/mL), and hypophosphatemia (median, 3.0 mg/dL; range, 2.4-3.9 mg/dL). The median serum 25-hydroxyvitamin D level was 7.44 ng/mL (range, 1.44-9.82 ng/mL). After vitamin D supplementation was initiated, serum phosphorus levels normalized within 1 month, and serum intact parathyroid hormone levels returned to the normal range within 2 months. Six of the 10 patients had serum alkaline phosphatase levels close to the normal range within 3 months. All 10 patients exhibited complete bone healing within 6 months of vitamin D treatment.

CONCLUSION

Nutritional rickets is not as rare in Taiwan as previously thought. When physicians encounter infants or toddlers with typical bone deformities or hypocalcemic seizures, a high index of suspicion and a detailed nutritional history are important for early diagnosis and treatment.

Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Vitamin D requires a two-step activation by hydroxylation: The first step is catalyzed by hepatic 25-hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α-hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25-(OH)₂ D. Mutations of CYP2R1 have been associated with vitamin D-dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss-of-function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss-of-function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25-OH-D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25-(OH)₂ D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa-hydroxyvitamin D₃ or alfacalcidol (1α-OH-D₃ ) treatment, and we observed a dramatic increase in the 1,25-(OH)₂ D serum concentration, which indicated the role of accessory 25-hydroxylase enzymes. Lastly, in patients who received calcifediol (25-OH-D₃ ), we documented normal 24-hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25-OH-D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency. © 2017 American Society for Bone and Mineral Research.

Global Consensus Recommendations on Prevention and Management of Nutritional Rickets

BACKGROUND

Vitamin D and calcium deficiencies are common worldwide, causing nutritional rickets and osteomalacia, which have a major impact on health, growth, and development of infants, children, and adolescents; the consequences can be lethal or can last into adulthood. The goals of this evidence-based consensus document are to provide health care professionals with guidance for prevention, diagnosis, and management of nutritional rickets and to provide policy makers with a framework to work toward its eradication.

EVIDENCE

A systematic literature search examining the definition, diagnosis, treatment, and prevention of nutritional rickets in children was conducted. Evidence-based recommendations were developed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system that describes the strength of the recommendation and the quality of supporting evidence.

PROCESS

Thirty-three nominated experts in pediatric endocrinology, pediatrics, nutrition, epidemiology, public health, and health economics evaluated the evidence on specific questions within five working groups. The consensus group, representing 11 international scientific organizations, participated in a multiday conference in May 2014 to reach a global evidence-based consensus.

RESULTS

This consensus document defines nutritional rickets and its diagnostic criteria and describes the clinical management of rickets and osteomalacia. Risk factors, particularly in mothers and infants, are ranked, and specific prevention recommendations including food fortification and supplementation are offered for both the clinical and public health contexts.

CONCLUSION

Rickets, osteomalacia, and vitamin D and calcium deficiencies are preventable global public health problems in infants, children, and adolescents. Implementation of international rickets prevention programs, including supplementation and food fortification, is urgently required.

Bone loss in chronic kidney disease: Quantity or quality?

Chronic kidney disease (CKD) patients experience bone loss and fracture because of a specific CKD-related systemic disorder known as CKD-mineral bone disorder (CKD-MBD). The bone turnover, mineralization, and volume (TMV) system describes the morphological bone lesions in renal osteodystrophy related to CKD-MBD. Bone turnover and bone volume are defined as high, normal, or low, and bone mineralization is classified as normal or abnormal. All types of bone histology related to TMV are responsible for both bone quantity and bone quality losses in CKD patients. This review focuses on current bone quantity and bone quality losses in CKD patients and finally discusses potential therapeutic measures.

Global Consensus Recommendations on Prevention and Management of Nutritional Rickets

BACKGROUND

Vitamin D and calcium deficiencies are common worldwide, causing nutritional rickets and osteomalacia, which have a major impact on health, growth, and development of infants, children, and adolescents; the consequences can be lethal or can last into adulthood. The goals of this evidence-based consensus document are to provide health care professionals with guidance for prevention, diagnosis, and management of nutritional rickets and to provide policy makers with a framework to work toward its eradication.

EVIDENCE

A systematic literature search examining the definition, diagnosis, treatment, and prevention of nutritional rickets in children was conducted. Evidence-based recommendations were developed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system that describe the strength of the recommendation and the quality of supporting evidence.

PROCESS

Thirty-three nominated experts in pediatric endocrinology, pediatrics, nutrition, epidemiology, public health, and health economics evaluated the evidence on specific questions within five working groups. The consensus group, representing 11 international scientific organizations, participated in a multiday conference in May 2014 to reach a global evidence-based consensus.

RESULTS

This consensus document defines nutritional rickets and its diagnostic criteria and describes the clinical management of rickets and osteomalacia. Risk factors, particularly in mothers and infants, are ranked, and specific prevention recommendations including food fortification and supplementation are offered for both the clinical and public health contexts.

CONCLUSION

Rickets, osteomalacia, and vitamin D and calcium deficiencies are preventable global public health problems in infants, children, and adolescents. Implementation of international rickets prevention programs, including supplementation and food fortification, is urgently required.

Urinary calcium to creatinine ratio: a potential marker of secondary hyperparathyroidism in patients with vitamin D-dependent rickets type 1A

Patients with vitamin D-dependent rickets type 1A (VDDR1A) are usually treated with alfacalcidol, an analog of vitamin D. Around puberty, an increased dose of alfacalcidol is recommended for these patients to avoid hypocalcemia and secondary hyperparathyroidism. However, no indicators of secondary hyperparathyroidism except for PTH are presently known. The aim of this study is to evaluate whether urinary calcium to creatinine ratio (U-Ca/Cr) is useful as a biomarker of secondary hyperparathyroidism in VDDR1A patients in order to determine the proper dose of alfacalcidol. Two brothers with VDDR1A were recruited who had null mutations of CYP27B1 which encodes 1-alpha-hydroxylase of vitamin D. We investigated the relationship between U-Ca/Cr and intact-PTH around puberty when the brothers showed hypocalcemia with secondary hyperparathyroidism. The results were compared to those of five patients with vitamin D deficiency (VDD). As a result, high intact-PTH levels were observed when U-Ca/Cr decreased to less than 0.1 (mg/mg) in both VDDR1A brothers. This relationship was also observed in the VDD patients. However, it is necessary to take into account body calcium status, either in depletion or in excess, to accurately evaluate the relationship between U-Ca/Cr and secondary hyperparathyroidism. First, low U-Ca/Cr was detected in situations with calcium depletion without hyperparathyroidism in the VDDR1A patients. Second, high U-Ca/Cr with hyperparathyroidism could be detected theoretically in a condition of excess calcium supply. In conclusion, a U-Ca/Cr ratio of less than 0.1 (mg/mg) in VDDR1A patients is useful to accurately evaluate calcium depletion and secondary hyperparathyroidism.

Vitamin D/dietary calcium deficiency rickets and pseudo-vitamin D deficiency rickets

This review describes the pathogenesis, clinical presentation and biochemical perturbations found in privational (nutritional) rickets and pseudo-vitamin D deficiency rickets (PDDR), an autosomal recessive condition with loss of function mutations in CYP27B1. It may seem strange to combine a discussion on privational rickets and PDDR as a single topic, but privational rickets and PDDR present with similar clinical signs and symptoms and with similar perturbations in bone and mineral metabolism. Of interest is the characteristic lack of features of rickets at birth in infants with PDDR, a finding which has also been reported in infants born to vitamin D-deficient mothers. This highlights the independence of the fetus and neonate from the need for vitamin D to maintain calcium homeostasis during this period. The variable roles of vitamin D deficiency and dietary calcium deficiency in the pathogenesis of privational rickets are discussed and the associated alterations in vitamin D metabolism highlighted. Although PDDR is a rare autosomal recessive disorder, results of long-term follow-up are now available on the effect of treatment with calcitriol, and these are discussed. Areas of uncertainty, such as should affected mothers breastfeed their infants, are emphasized.

A review on vitamin d deficiency treatment in pediatric patients

Vitamin D is essential for calcium absorption and for maintaining bone health in the pediatric population. Vitamin D deficiency may develop from nutritional deficiencies, malabsorption, enzyme-inducing medications, and many other etiologies. It may present as hypocalcemia before bone demineralization at periods of increased growth velocity (infancy and adolescence) because the increased calcium demand of the body cannot be met. In children, inadequate concentrations of vitamin D may cause rickets and/or symptomatic hypocalcemia, such as seizures or tetany. In this review, we will discuss the pharmacology behind vitamin D supplementation, laboratory assessments of vitamin D status, current literature concerning vitamin D supplementation, and various supplementation options for the treatment of vitamin D deficiency in the pediatric population.

Two teenage males with hypocalcemia and elevated parathyroid hormone levels

Vitamin D deficiency is not a rare disorder, particularly in minority groups. The Institute of Medicine recommends serum 25-hydroxyvitamin (OH)D levels >20 ng/mL and The Endocrine Society recommends levels >30 ng/mL for good health. In contrast, the 2003-2006 National Health and Nutrition Examination Survey reported average total 25-(OH)D concentrations of 25.6 ± 0.4 ng/mL in whites, 19.5 ± 0.5 ng/mL in Mexican Americans, and 14.8 ± 0.4 ng/mL in blacks. Pediatric patients with vitamin D deficiency may be asymptomatic or may present either with rickets, hypocalcemia, or seizures. Pseudohypoparathyroidism (PHP) is a rare disorder characterized by parathyroid hormone (PTH) resistance with (type 1a) or without (type 1b) the Albright Hereditary Os-teodystrophy (AHO) phenotype of short stature, brachydactyly, and mental retardation. Patients with PHP have elevated PTH levels and may have hyperphosphatemia and hypocalcemia. However, the same laboratory values can be seen in children with vitamin D deficiency, and diagnostic confusion is common. We report two cases of vitamin D deficiency with presentations suggestive of PHP.

Clinical practice: diagnostic approach to the rachitic child

Rickets remains a common problem among infants and children in many countries worldwide. Although the classical presentation associated with bone abnormalities is well known, paediatricians need to be aware of atypical presentations, especially in the first 6 months of life. Furthermore, although vitamin D deficiency rickets remains the commonest form of rickets in most countries, health care providers need to be aware of other possible causes and their typical clinical and biochemical presentations. This article discusses these and highlights the characteristic features of various forms of rickets and possible pitfalls clinicians should be aware of when confronted with a patient with suspected rickets. In conclusion, the recent advances made in understanding the underlying pathogeneses of the various forms of rickets has helped to delineate the diagnostic tests that assist in the diagnosis and management of the disease in children.

Vitamin D deficiency rickets mimicking pseudohypoparathyroidism

Vitamin D deficiency rickets (VDDR) is a disorder biochemically characterized by elevated serum alkaline phosphatase (ALP) activity, normal or decreased serum calcium (Ca) and inorganic phosphate concentrations, secondary hyperparathyroidism and decreased serum 25-hydroxyvitamin D (25(OH)D) levels. In stage 1 VDDR, urinary amino acid and phosphate excretion are normal with minimal or no findings of rickets on radiographs. Pseudohypoparathyroidism (PHP) is an inherited disorder characterized by end-organ resistance to parathormone (PTH). VDDR occasionally resembles PHP type 2 in clinical presentation and biochemical features, creating difficulties in the differential diagnosis of these two entities. Here we report an infant diagnosed with VDDR. In addition to inadequate vitamin D intake, usage of antiepileptic drugs (AED) may have led to the worsening of the vitamin D deficiency. The patient presented with a history of febrile convulsions, for which he received phenobarbital treatment. The initial findings of hypocalcemia, hyperphosphatemia and normal tubular reabsorption of phosphate, mimicking PHP 2, responded well to vitamin D and oral Ca treatment with normalization of serum Ca, phosphorus (P), ALP and PTH levels.

Nutritional deficiencies during normal growth

Nutritional deficiencies have always been a major consideration in pediatrics. Although the classic forms of many of the well-documented nutritional deficiencies are memorized during training as a physician, nutritional deficiencies that can occur in otherwise asymptomatic normally growing children are often overlooked. The two most common deficiencies seen in children who are growing normally are iron and vitamin D deficiencies. These deficiencies are surprisingly common and can have a significant impact on the overall health of a child. This article reviews these nutritional deficiencies and other less commonly seen deficiencies in children who are otherwise growing normally.

Vitamin D deficiency in children and adolescents: epidemiology, impact and treatment

Vitamin D deficiency is highly prevalent among children and adolescents worldwide. The high rates of vitamin D deficiency during childhood are of major public health relevance, given the growing evidence that vitamin D deficiency may play a key role in the pathophysiology of many chronic diseases beyond rickets, including autoimmune conditions, cardiovascular diseases, and cancer. Identification, treatment, and prevention of vitamin D deficiency in childhood may therefore have profound health effects throughout the life span. In this review, we discuss the definitions, epidemiology, clinical implications, and treatment of vitamin D deficiency in children and adolescents.

Ectopic thymic parathyroid adenoma and vitamin D deficiency rickets: a 5-year-follow-up case report and review of literature

Sixteen patients with primary hyperparathyroidism presenting as rickets have so far been reported in the English literature. However, no report of an ectopic thymic parathyroid adenoma presenting as rickets has been published. We report a 14-year-old Caucasian American, wheelchair-ridden male who presented with signs and symptoms suggestive of vitamin D deficiency rickets subsequently confirmed by laboratory and radiological findings. Following the intramuscular administration of 125,000 U ergocalciferol (vitamin D2), he developed hypercalcemia with persistently elevated parathyroid hormone (PTH) levels suggestive of primary hyperparathyroidism. Sestamibi scan demonstrated significant uptake in the superior chest, without uptake at the normal parathyroid glands location. Surgical exploration revealed normal parathyroid glands and a thymic mass, which was removed and confirmed by pathology to be a parathyroid adenoma. With subsequent oral ergocalciferol solution and calcium carbonate therapies, the patient's symptoms resolved, blood chemistries normalized, and radiological evidence of rickets significantly improved. To our knowledge, this is the first case of an ectopic thymic parathyroid adenoma in a patient presenting with rickets. Our patient demonstrates that hyperparathyroidism-induced hypercalcemia may be masked by severe vitamin D deficiency. Prolonged treatment with ergocalciferol after removal of the parathyroid adenoma was necessary to normalize iPTH and replenish vitamin D store.

Doing the month: rickets and post-partum convalescence in rural China

OBJECTIVE

to analyse the health beliefs underlying the Chinese custom of 'doing the month', in particular mothers' perceptions of rickets.

DESIGN

a qualitative approach was used. Four focus group discussions were tape recorded. Translated transcripts were analysed and coded.

SETTING

Yuci District, rural Shanxi Province, China.

PARTICIPANTS

eighteen young mothers with children aged between 12 and 24 months, five grandmothers aged between 48 and 55 years, five township clinic maternal and child health workers, and seven traditional medicine doctors.

FINDINGS

Zuo yuezi (doing the month) is accepted by Chinese mothers as a time of respite and physical recovery. It is also burdensome to mothers, as cloistering indoors compromises both mother and baby's exposure to the sun, resulting in vitamin D deficiency and rickets.

KEY CONCLUSIONS

in order to reduce the rates of rickets in children, it is important to promote a more balanced and health-enhancing form of zuo yuezi that maintains necessary vitamin D status of both the mother and her baby. By understanding this custom, medical professionals caring for pregnant and post-partum Chinese women in Western countries will be able to better serve their health needs.

Diagnosis of rickets and reassessment of prevalence among rural children in northern China

BACKGROUND

Rates of rickets from 15.9 to 26.7% have been reported in China.

METHODS

Combining the methods of epidemiology and the behavioral sciences, this study investigated the prevalence of rickets in children in rural Shanxi Province, China. A total of 250 children age 12-24 months were examined physically for the presence of rickets, blood was drawn for laboratory analysis, and X-rays were taken of each child's wrists.

RESULTS

Vitamin D deficiency in the spring was found among 65.3% of children. Rickets diagnosis relying on clinical signs alone determined a rickets prevalence of 41.6%, declining to 17.0% in the fall after a summer of sun exposure (chi(2) = 8.356, P = 0.004). But an integrated diagnostic method exploiting clinical signs, X-ray and alkaline phosphatase levels found the prevalence of active rickets to be 3.7%. Furthermore, it was demonstrated that only five clinical signs reflect active rickets--wide wrists, frontal bossing, rachitic rosary, Harrison's sulcus, and bowed legs.

CONCLUSIONS

The prevalence of active rickets in young children in northern China is lower than previously reported. Even in poor countries, simple tests such as X-rays and alkaline phosphatase can be added to physical examination to more accurately diagnose active rickets.

Early response to vitamin D2 in children with calcium deficiency rickets

OBJECTIVE

To assess the effect of vitamin D(2) administration on serum vitamin D metabolite concentrations in calcium deficiency rickets.

STUDY DESIGN

We administered vitamin D(2), 50,000 IU orally to 16 Nigerian children 15 to 48 months of age with radiographically active rickets. We measured calcium and vitamin D metabolites at baseline and at 1, 3, 7, and 14 days.

RESULTS

At baseline, ranges of serum 25-hydroxyvitamin D (25(OH)D) concentrations were 18 to 40 nmol/L (7-16 ng/mL), and 1,25-dihydroxyvitamin D (1,25-(OH)(2)D) concentrations were 290 to 790 pmol/L (120-330 pg/mL). After vitamin D administration, serum 25(OH)D and 1,25(OH)(2)D concentrations rapidly rose and peaked at 2.8 and 1.9 times the baseline values (P < .001), respectively, at 3 days. Positive correlations between 1,25(OH)(2)D and 25(OH)D were strongest at day 3 (r = 0.84, P < .001) and weakest at day 14 (r = 0.41, P = .11). The relationship of 1,25(OH)(2)D with 25(OH)D at baseline and the increase in 1,25(OH)(2)D in response to vitamin D were similar to those described in children with vitamin D deficiency. However, unlike the pattern in vitamin D deficiency, 1,25(OH)(2)D remained positively correlated with 25(OH)D after administration of vitamin D.

CONCLUSION

Dietary calcium deficiency increases the demand for 25(OH)D above that required in vitamin D deficiency to optimize 1,25(OH)(2)D concentrations. Assessment of vitamin D sufficiency in persons or communities may need to be adjusted for habitual dietary calcium intake.

Metabolic Bone Disease in Children

Metabolic bone disease in children includes many hereditary and acquired conditions of diverse etiology that lead to disturbed metabolism of the bone tissue. Some of these processes primarily affect bone; others are secondary to nutritional deficiencies, a variety of chronic disorders, and/or treatment with some drugs. Some of these disorders are rare, but some present public health concerns (for instance, rickets) that have been well known for many years but still persist. The most important clinical consequences of bone metabolic diseases in the pediatric population include reduced linear growth, bone deformations, and non-traumatic fractures leading to bone pain, deterioration of motor development and disability. In this article, we analyze primary and secondary osteoporosis, rickets, osteomalacia (nutritional and hereditary vitamin D-dependent, hypophosphatemic and that due to renal tubular abnormalities), renal osteodystrophy, sclerosing bony disorders, and some genetic bone diseases (hypophosphatasia, fibrous dysplasia, skeletal dysplasia, juvenile Paget disease, familial expansile osteolysis, and osteoporosis pseudoglioma syndrome). Early identification and treatment of potential risk factors is essential for skeletal health in adulthood. In most conditions it is necessary to ensure an appropriate diet, with calcium and vitamin D, and an adequate amount of physical activity as a means of prevention. In secondary bone diseases, treatment of the primary disorder is crucial. Most genetic disorders await prospective gene therapies, while bone marrow transplantation has been attempted in other disorders. At present, affected patients are treated symptomatically, frequently by interdisciplinary teams. The role of exercise and pharmacologic therapy with calcium, vitamin D, phosphate, bisphosphonates, calcitonin, sex hormones, growth hormone, and thiazides is discussed. The perspectives on future therapy with insulin-like growth factor-1, new analogs of vitamin D, strontium, osteoprotegerin, and calcimimetics are presented.

Renal tubular toxicity associated with tenofovir assessed using urine-beta 2 microglobulin, percentage of tubular reabsorption of phosphate and alkaline phosphatase levels

Despite its wide use, the renal tubular toxicity of tenofovir has not been fully evaluated. Twelve weeks after initiating a tenofovir-containing HAART regimen, a high urine-beta 2 microglobulin level was observed in 12 out of 17 patients, the percentage of tubular reabsorption of phosphate decreased from 96.0 to 91.1% and alkaline phosphatase increased from 294 to 365 U/l, whereas serum creatinine and phosphorus remained largely unchanged. Patients with the above findings should be monitored carefully for renal tubular toxicity.

Nutritional rickets: deficiency of vitamin D, calcium, or both?

Nutritional rickets remains a public health problem in many countries, despite dramatic declines in the prevalence of the condition in many developed countries since the discoveries of vitamin D and the role of ultraviolet light in prevention. The disease continues to be problematic among infants in many communities, especially among infants who are exclusively breast-fed, infants and children of dark-skinned immigrants living in temperate climates, infants and their mothers in the Middle East, and infants and children in many developing countries in the tropics and subtropics, such as Nigeria, Ethiopia, Yemen, and Bangladesh. Vitamin D deficiency remains the major cause of rickets among young infants in most countries, because breast milk is low in vitamin D and its metabolites and social and religious customs and/or climatic conditions often prevent adequate ultraviolet light exposure. In sunny countries such as Nigeria, South Africa, and Bangladesh, such factors do not apply. Studies indicated that the disease occurs among older toddlers and children and probably is attributable to low dietary calcium intakes, which are characteristic of cereal-based diets with limited variety and little access to dairy products. In such situations, calcium supplements alone result in healing of the bone disease. Studies among Asian children and African American toddlers suggested that low dietary calcium intakes result in increased catabolism of vitamin D and the development of vitamin D deficiency and rickets. Dietary calcium deficiency and vitamin D deficiency represent 2 ends of the spectrum for the pathogenesis of nutritional rickets, with a combination of the 2 in the middle.

Treatment of anticonvulsant drug-induced bone disease

Although the pathophysiology of bone disease in patients treated with anticonvulsant drugs may vary, most affected patients have increased bone remodeling rather than decreased mineralization. Milder cases may show high bone turnover without significant loss of cortical or trabecular bone. Cases of intermediate severity may exhibit the characteristic features of a high-turnover osteopenia/osteoporosis, but some patients with severe bone disease may manifest the features of an osteomalacic disorder. Prophylactic vitamin D supplementation at doses up to 2000 IU/day can be recommended for all patients on initiation of anticonvulsant therapy. A calcium intake of 600-1000 mg/day should also be ensured. If an osteopenic/osteoporotic disorder exists, treatment with 2000-4000 IU/day vitamin D is appropriate. Vitamin D doses of 5000-15,000 IU/day may be needed to treat osteomalacia. Conventional treatment with bisphosphonates may be needed when the response to vitamin D is inadequate. However, routine use of bisphosphonates in patients receiving long-term anticonvulsant therapy cannot at present be recommended.

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.

Rickets as an unusual initial presentation of abetalipoproteinemia and hypobetalipoproteinemia

OBJECTIVE

Description of rickets as an unexpected initial manifestation in two children with abetalipoproteinemia and hypobetalipoproteinemia, and elucidation of its pathophysiology in these conditions.

METHODOLOGY

Two infants aged two and six months with abetalipoproteinemia and hypobetalipoproteinemia respectively had clinical rickets at presentation, confirmed radiologically and biochemically. Vitamin D intake and serum levels were measured and other causes of rickets were looked for.

RESULTS

Vitamin D intake and laboratory studies levels were suggestive of rickets due to calcium deficiency instead of vitamin D deficiency. Healing of rickets occurred with dietary treatment of the malabsorption, without any dietary calcium or significant vitamin D supplementation.

CONCLUSION

Steatorrhea-induced calcium malabsorption seems to be the most likely cause of rickets in this entity.

1alpha,25-dehydroxyvitamin D3 synergism toward transforming growth factor-beta1-induced AP-1 transcriptional activity in mouse osteoblastic cells via its nuclear receptor

The present study demonstrates 1alpha,25-dehydroxyvitamin D3 (1alpha-25-(OH)2D3) synergism toward transforming growth factor (TGF)-beta1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1alpha-25-(OH)2D3 synergistically stimulated TGF-beta1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. We actually showed by a gel mobility shift assay 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1alpha-25-(OH)2D3 markedly stimulated the transient activity of TGF-beta1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene. Also, a synergistic increase in TGF-beta1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. However, the synergistic CAT activity was inhibited by pretreatment with VDR antisense oligonucleotides. In addition, in a Northern blot assay, we observed 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and also found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. The present study strongly suggests a novel positive regulation by 1alpha-25-(OH)2D3 of TGF-beta1-induced AP-1 activity in osteoblasts via "genomic action."

Laboratory assessment of nutritional metabolic bone disease in infants

OBJECTIVES

There are numerous laboratory investigations available for the assessment of an infant with suspected metabolic bone disease (MBD); thus, comprehensive laboratory investigations on every aspect of MBD would impose unnecessary stress to the infant and the costs involved would be prohibitive. An overview of the assessment of an infant with suspected MBD, in particular, nutrition-related bone disease, is presented. Our objectives include an understanding of: 1. the importance of appropriate information from history and physical examination to guide the laboratory investigations; 2. relevance and limitations of specific laboratory investigations: a. radiologic studies include diagnostic radiographs and quantitative bone mass determination by dual energy x-ray absorptiometry, b. biochemical measurements to determine mineral homeostasis and bone turnover, c. vitamin (vitamin D metabolites) and hormonal (parathyroid hormone and calcitonin) measurements; with respect to diagnosis and monitoring of the natural progress or response to therapy.

CONCLUSION

Relevant information from clinical history and physical examination, and an understanding of the role and limitations of various laboratory investigations, would allow the optimal utilization of laboratory tests in the assessment of an infant with MBD.