Stage I vitamin D-deficiency rickets mimicking pseudohypoparathyroidism type II

Vitamin D Deficiency Prevalence in Late Neonatal Hypocalcemia: A Multicenter Study

OBJECTIVE

Late neonatal hypocalcemia (LNH) is a common metabolic problem associated with hypoparathyroidism, high phosphate intake and vitamin D deficiency, often presenting with seizures. In this cross-sectional study, we aimed to evaluate the role of vitamin D deficiency in LNH in Turkey and to describe the characteristics of affected newborns.

METHODS

Conducted with a cross-sectional design and with the participation of 61 neonatal centers from December 2015 to December 2016, the study included term neonates with LNH (n=96) and their mothers (n=93). Data were registered on the FAVOR Web Registry System. Serum samples of newborns and mothers were analyzed for calcium, phosphate, magnesium, albumin, alkaline phosphatase, intact parathyroid hormone (iPTH) and 25 hydroxyvitamin D [25(OH)D] levels.

RESULTS

The median (range) onset time of hypocalcemia was 5.0 (4.0-8.0) days of age, with a male preponderance (60.4%). The median (range) serum 25(OH)D levels of the neonates and their mothers were 6.3 (4.1-9.05) and 5.2 (4.7-8.8) ng/mL, respectively. The prevalence of vitamin D deficiency (<12 ng/mL) was high in both the neonates (86.5%) and mothers (93%). Serum 25(OH)D levels of the infants and mothers showed a strong correlation (p<0.001). While the majority (93.7%) of the neonates had normal/high phosphorus levels, iPTH levels were low or inappropriately normal in 54.2% of the patients.

CONCLUSION

Vitamin D deficiency prevalence was found to be high in LNH. Efforts to provide vitamin D supplementation during pregnancy should be encouraged. Evaluation of vitamin D status should be included in the workup of LNH.

Nutritional rickets & osteomalacia: A practical approach to management

Defective mineralization of the growth plate and preformed osteoid result in rickets and osteomalacia, respectively. The leading cause of rickets worldwide is solar vitamin D deficiency and/or dietary calcium deficiency collectively termed as nutritional rickets. Vitamin D deficiency predominates in high-latitude countries in at-risk groups (dark skin, reduced sun exposure, infants and pregnant and lactating women) but is emerging in some tropical countries due to sun avoidance behaviour. Calcium deficiency predominates in tropical countries, especially in the malnourished population. Nutritional rickets can have devastating health consequences beyond bony deformities (swollen wrist and ankle joints, rachitic rosary, soft skull, stunting and bowing) and include life-threatening hypocalcaemic complications of seizures and, in infancy, heart failure due to dilated cardiomyopathy. In children, diagnosis of rickets (always associated with osteomalacia) is confirmed on radiographs (cupping and flaring of metaphyses) and should be suspected in high risk individuals with the above clinical manifestations in the presence of abnormal blood biochemistry (high alkaline phosphatase and parathyroid hormone, low 25-hydroxyvitamin D and calcium and/or low phosphate). In adults or adolescents with closed growth plates, osteomalacia presents with non-specific symptoms (fatigue, malaise and muscle weakness) and abnormal blood biochemistry, but only in extreme cases, it is associated with radiographic findings of Looser's zone fractures. Bone biopsies could confirm osteomalacia at earlier disease stages, for definitive diagnosis. Treatment includes high-dose cholecalciferol or ergocalciferol daily for a minimum of 12 wk or stoss therapy in exceptional circumstances, each followed by lifelong maintenance supplementation. In addition, adequate calcium intake through diet or supplementation should be ensured. Preventative approaches should be tailored to the population needs and incorporate multiple strategies including targeted vitamin D supplementation of at-risk groups and food fortification with vitamin D and/or calcium. Economically, food fortification is certainly the most cost-effective way forward.

The relation between circulating levels of vitamin D and parathyroid hormone in children and adolescents with overweight or obesity: Quest for a threshold

The level of serum 25-hydroxyvitamin D (25(OH)D) at which intact parathyroid hormone (iPTH) is maximally suppressed (suppression point) and below which PTH begins to rise (inflection point) has been used to define optimum 25(OH)D concentration. We aimed to study the association of circulating iPTH with 25(OH)D concentrations and to determine a 25(OH)D threshold associated with a significant iPTH suppression. This cross-sectional study was conducted on 198 boys and 180 girls, aged 6–13 years with BMI ≥ 1SD (WHO criteria) recruited from primary schools. Adjusted iPTH for BMI z-score, pubertal status, and dietary calcium was used. Nonlinear regression was used to model the relationship between 25(OH)D and iPTH and identify a suppression point for 25(OH)D at which iPTH reached a plateau. Piecewise regression analysis with a single knot for all possible values of 25(OH)D were fitted. Furthermore, 95% confidence intervals (95%CI) for those point had been calculated. The mean age (SD) of girls and boys was 9.1 (1.6) and 9.4 (1.7) years, respectively. Median 25(OH)D and iPTH were 13.8 ng/mL and 33.9 pg/mL in boys and 9.9 ng/mL and 47.8 ng/mL in girls, respectively. The equation in girls was: log-iPTH = 3.598+0.868 exp[(-0.190×25(OH)D. The point for near maximal suppression of iPTH by 25(OH)D for girls occurred at a 25(OH)D concentration of 20 ng/mL (95% CI: 7.1 to 32.2). No point of maximal suppression was found for boys. We also found a 25(OH)D threshold of 10 ng/mL (95% CI: 4.6 to 22.5) for girls (f: 9.8) by linear piecewise regression modeling of adjusted iPTH. No significant inflection point for boys was observed. In overweight/obese girls, when the concentration of 25(OH)D was higher than 20 ng/mL, an iPTH mean plateau level is reached, and when its concentrations approach 10 ng/mL, the slope of iPTH concentration has been accelerated.

Hypoparathyroidism

Hypoparathyroidism is a disease characterized by inadequately low circulating concentrations of parathyroid hormone (PTH) resulting in low calcium levels and increased phosphate levels in the blood. Symptoms of the disease result from increased neuromuscular irritability caused by hypocalcaemia and include tingling, muscle cramps and seizures. The most common cause of the disease is inadvertent removal of, or injury to, the parathyroid glands during neck surgery, followed by genetic, idiopathic and autoimmune aetiologies. Conventional treatment includes activated vitamin D and/or calcium supplements, but this treatment does not fully replace the functions of PTH and can lead to short-term problems (such as hypocalcaemia, hypercalcaemia and increased urinary calcium excretion) and long-term complications (which include nephrocalcinosis, kidney stones and brain calcifications). PTH replacement has emerged as a new treatment option. Clinical trials using human PTH(1-34) and PTH(1-84) showed that this treatment was safe and effective in studies lasting up to 6 years. Recombinant human PTH(1-84) has been approved in the United States and Europe for the management of hypoparathyroidism; however, its effect on long-term complications is still being evaluated. Clinical practice guidelines, which describe the consensus of experts in the field, have been published and recognize the need for more research to optimize care. In this Primer, we summarize current knowledge of the prevalence, pathophysiology, clinical presentation and management of hypoparathyroidism.

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.

Hypophosphatemic rickets due to perturbations in renal tubular function

The common denominator for all types of rickets is hypophosphatemia, leading to inadequate supply of the mineral to the growing bone. Hypophosphatemia can result from insufficient uptake of the mineral from the gut or its disproportionate losses in the kidney, the latter being caused by either tubular abnormalities per se or the effect on the tubule of circulating factors like fibroblast growth factor-23 and parathyroid hormone (PTH). High serum levels of the latter result in most cases from abnormalities in vitamin D metabolism which lead to decreased calcium absorption in the gut and hypocalcemia, triggering PTH secretion. Rickets is a disorder of the growth plate and hence pediatric by definition. However, it is important to recognize that the effect of hypophosphatemia on other parts of the skeleton results in osteomalacia in both children and adults. This review addresses the etiology, pathophysiologic mechanisms, clinical manifestations and treatment of entities associated with hypophosphatemic rickets due to perturbations in renal tubular function.

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.

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.

The clinical characteristics of vitamin D deficiency in childhood: a systematic literature review of Japanese patients

To describe the characteristics of children with vitamin D deficiency, we reviewed the reports of vitamin D deficiency among Japanese children that were published between 1989 and 2008. We identified 25 patients with vitamin D deficiency in 9 published studies and evaluated their clinical characteristics together with those of 3 patients we recently treated. The patients were distributed in two distinct age groups at diagnosis: < 1 year old and > or = 1 year old. The main symptom of the < 1 year old age group was hypocalcemic convulsions and that of the > or = 1 year old age group was bowed legs. Serum calcium, intact PTH, and 1,25(OH)2D levels were significantly lower in the < 1 year age group than in the > or = 1 year age group. It would be useful to find and make early interventions in cases of children at a high-risk of vitamin D deficiency.

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.

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.