Mucolipidosis II presenting as severe neonatal hyperparathyroidism

Mucolipidosis II (ML II or I-cell disease ) (OMIM 252500) is an autosomal recessive lysosomal enzyme targeting disorder that usually presents between 6 and 12 months of age with a clinical phenotype resembling Hurler syndrome and a radiological picture of dysostosis multiplex. When ML II is severe enough to be detected in the newborn period, the radiological changes have been described as similar to hyperparathyroidism or rickets. The biological basis of these findings has not been explored and few biochemical measurements have been recorded. We describe three unrelated infants with ML II who had radiological features of intrauterine hyperparathyroidism and biochemical findings consistent with severe secondary neonatal hyperparathyroidism (marked elevation of serum parathyroid hormone and alkaline phosphatase levels). The vitamin D metabolites were not substantially different from normal and repeatedly normal calcium concentrations excluded vitamin D deficiency rickets and neonatal severe hyperparathyroidism secondary to calcium-sensing receptor gene mutations (OMIM 239200). The pathogenesis of severe hyperparathyroidism in the fetus and newborn with ML II is unexplained. We hypothesize that the enzyme targeting defect of ML II interferes with transplacental calcium transport leading to a calcium starved fetus and activation of the parathyroid response to maintain extracellular calcium concentrations within the normal range. Conclusion: Newborns with mucolipidosis II can present with radiological and biochemical signs of hyperparathyroidism. Awareness of this phenomenon may help in avoiding diagnostic pitfalls and establishing a proper diagnosis and therapy.Some material from this paper was presented at the 6th International Skeletal Dysplasia Conference in Warrenton, Virginia, August 22, 2003.     

Rickets-like radiological and biochemical features of neonatal mucolipidosis II (I-cell disease): report of two cases

In this paper, two cases with mucolipidosis type II (I-cell disease) (proven in one presenting newborn and presumed in an elder deceased brother) are presented. These infants showed severe skeletal changes with diffuse periosteal new bone formation in long bones and ribs, marked osteopenia, and resorption of scapula, clavicula, and mandible. There was also irregular demineralization of metaphyses of long tubular bones, as seen in rickets. The activities of serum alkaline phosphatase and parathyroid hormone were markedly elevated. Phosphorus was decreased. Serum 1,25-dihydroxyvitamin D was slightly elevated, but 25-hydroxyvitamin D and calcium were normal. Dysostosis multiplex resembling rickets and very high alkaline phosphatase activity were due to defective osteoblastic activity, but the mechanism of elevated parathyroid hormone was not clear. We conclude that early skeletal manifestation of mucolipidosis type II is not clearly identified and that differentiation from congenital rickets or congenital hyperparathyroidism could be difficult. It is speculated that hyperparathyroidism in these patients could be related to the calcium-sensing receptor malfunction in the parathyroid gland.     

Hypo-hyperparathyroidism: evidence for a defective parathyroid hormone.

Biochemical evidence for hypoparathyroidism and roentgenographic evidence for hyperparathyroidism were present in a 7-year-old girl with seizures and tetany. She was hypocalcemic (4.7 mg/dl), hyperphosphatemic (11 mg/dl), and normomagnesemic, with elevated parathyroid hormone level (2,603 pg/dl and 3,693 pg/dl in immunoassays utilizing two different antisera). Somatic features of pseudohypoparathyroidism were absent. Increased serum alkaline phosphatase activity (335 IU/liter) with evidence of subperiosteal bone resorption suggested parathyroid hormone activity on bone. Intramuscular administration of parathyroid extract caused a rise in serum calcium level (9.6 mg/dl) and a fall in serum phosphorus level (7.9 mg/dl). The serum calcium, phosphorus, and alkaline phosphatase activity became normal during vitamin D therapy. Parathyroid hormone values and bone roentgenograms became normal. With serum calcium and phosphorus levels normal, ethylenediaminetetraacetic acid infusion was followed by an increase in plasma parathyroid hormone level but not in urinary cyclic adenosine monophosphate (AMP) or phosphaturia; in contrast, parathyroid extract induced cyclic AMP excretion and phosphaturia. These results suggest that endogenous parathyroid hormone in this patient affects bone resorption but not renal handling of phosphate. We infer that this represents a defective endogenous parathyroid hormone.     

Renal osteodystrophy in children undergoing continuous ambulatory peritoneal dialysis

This paper describes a retrospective evaluation of the course of renal bone disease in 14 children undergoing treatment with continuous ambulatory peritoneal dialysis (CAPD) for an average of 11.9 +/- 1.5 months (mean +/- SE). The patients were divided in two groups according to the changes in serum alkaline phosphatase activity during the period of observation: five patients had alkaline phosphatase activity that decreased or was relatively stable (group I), and nine patients exhibited a rising serum alkaline phosphatase activity (group II). Serial radiological examinations showed adequate control of renal osteodystrophy in the patients of group I, whereas the patients of group II had no improvement or worsening of their bone disease. Group I had higher serum calcium and lower parathyroid hormone levels than group II at the end of period of observation despite similar dosage of vitamin D metabolite. The progression of bone disease was not related to the duration of CAPD or type of previous treatment for end stage renal disease. The observation that the radiological manifestations of secondary hyperparathyroidism were prevented in patients whose serum calcium levels were frequently above 2.62 mmol/liter (group I) while serum calcium levels between 2.25 and 2.50 mmol/liter in group II patients failed to lead to regression of secondary hyperparathyroidism is consistent with the existence of altered "set-point" regulation of the parathyroid gland in children undergoing CAPD.     

Serum levels of carboxyterminal propeptide of type I procollagen in healthy children from 1 st year of life to adulthood and in metabolic bone diseases

Type I collagen is the major component of bone matrix; circulating carboxyterminal propeptide of type I procollagen (P-I-CP) levels reflect type I collagen synthesis in tissues and may be an useful index to investigate bone metabolism. We measured P-I-CP by a new radioimmunoassay in 300 healthy children and adolescents and in 40 healthy adults to provide reference data for P-I-CP values. In addition, 79 patients with diagnosed disorders of phospho-calcium metabolism (rickets, vitamin D deficient and vitamin D resistant, hyperparathyroidism, hypo- and pseudo-hypoparathyroidism, osteopenia) were evaluated. In the healthy subjects, serum P-I-CP values were higher in children than in adults; variations of P-I-CP levels were observed according to age and sexual maturation: higher values were found in the first years of life and during pubertal development; pubertal increase reflects the different timing of pubertal development in the two sexes. P-I-CP levels were increased in primary hyperparathyroidism and reduced in diseases related to impaired secretion or action of parathyroid hormone. Higher P-I-CP levels were found in vitamin D deficient and vitamin D resistant rickets. P-I-CP was reduced in anorexia nervosa and during chronic glucocorticoid treatment while it was increased in thyrotoxic osteoporosis. In idiopathic juvenile osteoporosis, P-I-CP values ranged from reduced to increased values. We conclude that P-I-CP may represent an additional biochemical marker of bone metabolism. Since age-related variations are present, reference data for the various ages are need for clinical application of this assay.     

Biochemical markers of bone turnover,intact serum parathyroid hormone and renal calcium excretion in patients with pseudohypoparathyroidism and hypoparathyroidism before and during vitamin D treatment

In addition to the well-documented hyporesponsiveness of the kidney, resistance to parathyroid hormone (PTH) has been postulated for bone in pseudohypoparathyroidism type I (PHP). In some of these patients reduced bone density and even frank osteitis fibrosa suggest osteoclastic overactivity. To address the possibility that the skeletal system of patients with PHP may be affected by their increased PTH secretion we measured intact serum PTH and three biochemical markers of bone turnover in a large number of patients with PHP (n=20). The results were compared with subjects with low (hypoparathyroidism, HP, n=29), normal (controls, n=31) and high (primary hyperparathyroidism, 1°HPT, n=13) PTH secretion. Both markers of osteoblastic bone formation, alkaline phosphatase activity and osteocalcin concentration in serum, and one index of osteoclastic bone degradation, the urinary hydroxyproline/creatinine ratio (OH-P/Cr), were decreased in HP and increased in 1°HPT, whereas only OH-P/Cr was elevated in patients with PHP. Although intact serum PTH was significantly more increased in PHP than in 1°HPT, the markers of bone turnover were not significantly different in these two groups, suggesting some bone resistance in the patients with PHP. In these subjects intact serum PTH was elevated even at normocalcaemia during vitamin D treatment with a negative correlation with the respective serum calcium concentration (r=–0.69, P<0.001), indicating an elevated set-point for the suppression of their parathyroid glands. OH-P/Cr was negatively related to serum calcium in PHP, it normalized in most patients during normocalcaemia induced by vitamin D treatment. The urinary calcium excretion remained normal in the patients with PHP but was markedly elevated in patients with HP after the serum calcium levels had normalized during vitamin D therapy. In conclusion, the present and other studies suggest that the resistance to PTH in patients with PHP is mainly limited to the proximal kidney tubule and that the tendency to increased bone degradation implies either some response of the remodelling bone system to PTH or the result of marked secondary hyperparathyroidism overcoming a partial resistance of bone cells. The aim of vitamin D treatment in patients with PHP should therefore be an elevation of the serum calcium concentration into the high normal-range in order to suppress PTH secretion and thus bone degradation. In these patients the parathyroid glands are less sensitive to circulating calcium levels.Abbreviations AHO Albright's hereditary osteodystrophy - AMP adenosine monophosphate - AP alkaline phosphatase activity - Ca calcium - Ca/Cr urinary calcium/creatinine ratio - Cr creatinine - HP hypoparathyroidism - 1°HPT primary hyperparathyroidism - OH-P/Cr urinary hydroxyproline/creatinine ratio - PHP pseudohypoparathyroidism - PTH parathyroid hormone - SDS standard deviation score     

Parathyroid autotransplantation in renal osteodystrophy.

Severe renal osteodystrophy with metaphyseal fractures developed in two children with hypoplastic-dysplastic kidneys and chronic renal failure despite therapy with vitamin D, CaCO3, phosphate-binding agents, and protein restriction. Serum immunoreactive parathyroid hormone (iPTH) levels were elevated to 709 and 1,537 pg/mL (N = 255 +/- 92 pg/mL). Total parathyroidectomy and then autotransplantation of a small portion of parathyroids into the left brachioradialis muscle resulted in complete healing of renal osteodystrophy with the same dose of vitamin D. Serum iPTH and histological studies have demonstrated functioning parathyroid autotransplants, 19 and 20 months postoperatively in these two patients. Advantage of such a procedure over 3 3/4 parathyroidectomy is that this transplanted parathyroid tissue is easily accessible for partial removal in case of recurrence of uncontrollable hyperparathyroidism. We believe that total parathyroidectomy and autotransplantation can be successfully performed even in small children.     

Parenteral calcitriol for treatment of severe renal osteodystrophy in children with chronic renal insufficiency

Renal osteodystrophy is a common and incapacitating complication of chronic renal failure in children. Standard therapy with oral calcium supplements, phosphate binders, and vitamin D preparations is often inadequate to control progressive bone disease. We report the use of parenteral calcitriol therapy in two children, aged 2 and 15 years, respectively, with chronic renal failure. This treatment effectively suppressed secondary hyperparathyroidism in both patients, causing a nearly 50% reduction in circulating parathyroid hormone level and a parallel decline in serum alkaline phosphatase activity. In the younger patient, therapy was associated with healing of subperiosteal bone resorption and accelerated growth velocity. These findings indicate that parenteral administration of calcitriol may be an effective treatment option in some patients with refractory renal osteodystrophy and secondary hyperparathyroidism.     

Hepatic osteodystrophy in chronic cholestasis: evidence for a multifactorial etiology

Children with cholestatic liver disease have been thought to develop hepatic osteodystrophy resulting from vitamin D and calcium malabsorption, resulting in secondary hyperparathyroidism and osteomalacia or rickets. However, treatment with vitamin D has not always proven successful in improving the bone disturbance. The aim of our study was to determine the role of vitamin D deficiency in the pathogenesis of hepatic osteodystrophy. We studied five patients, three female and two male, ages 0.9-19 yr, with biopsy-proven chronic cholestatic liver disease and previously low serum levels of vitamin D despite oral intake of vitamin D preparations. Patients were admitted to the Clinical Research Center for 8 days for sunlight deprivation and ultraviolet light substitution and for determinations of serum 25-hyroxyvitamin D(25(OH)) D2 and -D3, osteocalcin, and type I collagen telopeptide (ICTP), the last two being markers of bone formation and resorption, respectively. Samples were taken on admission, at discharge, and 1 month later. Results demonstrated low serum levels of osteocalcin and normal circulating levels of ICTP. Admission serum 25(OH)D2 levels were uniformly low or undetectable and remained so. Admission levels of circulating 25(OH)D3 were normal or low and did not rise during ultraviolet light therapy or subsequent resumption of oral vitamin D therapy and remained low 1 month later. These results indicate that in the face of low-normal to low total 25(OH)D levels, the low osteocalcin and normal ICTP levels suggest that decreased bone formation and not increased bone resorption is the main determinant of bone loss in a subset of children with chronic cholestatic liver disease.     

Beneficial Effect of Oral Bisphosphonate Treatment on Bone Loss Induced by Chronic Administration of Furosemide without Alteration of Its Administration and Urinary Calcium Loss

Bisphosphonate is widely used to treat patients with primary and secondary osteoporosis. The chronic administration of furosemide is considered a risk factor for osteoporosis mainly due to the increased urinary excretion of calcium, leading to a long-term negative balance of calcium. We describe two patients with mild heart failure who took furosemide for more than 5 yr and developed hyperparathyroidism and lumbago associated with low bone mineral density. Their serum levels of intact parathyroid hormone and bone mineral density (BMD) of the lumbar spine (L2-L4) were 180.8 and 144.3 pg/ml, and 71% and 80% of the mean of healthy women, respectively. The oral administration of alendronate or risedronate was effective for lumbago and improved BMD, although the urinary excretion of calcium and hyperparathyroidism were not changed. For the medical treatment of lumbago and decreased bone mass secondary to the long-term administration of furosemide, bisphosphonate is proposed when the dose of furosemide cannot be reduced. However, it may be important to give sufficient calcium and vitamin D to patients to improve secondary hyperparathyroidism.     

Persistent elevated serum levels of intact parathyroid hormone after reoperation for primary hyperparathyroidism and after pamidronate therapy

Primary hyperparathyroidism is a life-threatening rare disorder. It is seen as a result of neonatal primary hyperparathyroidism, familial hypocalciuric hypercalcemia, increased vitamin D levels and inactivation of calcium sensing receptor mutations. The clinical findings are hypotonia, bone demineralization, hypercalcemia and parathyroid hyperplasia. We present a six-month-old female patient, the first child of nonconsanguineous parents, who was referred for the investigation of failure to thrive, vomiting, constipation, fever, abdominal distention and hypotonia. Physical examination revealed weight under 3rd percentile, height 3rd-10th percentile, decreased subcutaneous fat, and distention of the abdomen. In neurological examination, hypotonia, motor-mental retardation, and active deep tendon reflexes were found. The biochemical values at the time of admission revealed primary hyperparathyroidism. Since hypercalcemia did not respond to calcitonin therapy and due to the mortality of hypercalcemia, parathyroidectomy was performed. Because hyperparathyroidism and hypercalcemia continued, angiography was done which revealed increased parathyroid hormone levels in the periphery of the innominate vein. Exploratory surgery followed, but hyperparathyroidism and hypercalcemia persisted after all of these procedures. Calcium-sensing receptor mutations and supernumerary gland were considered. Because hypercalcemia persisted, pamidronate therapy was initiated on a monthly basis.     

Serum 1,25 dihydroxyvitamin D and osteocalcin concentrations in thalassaemia major.

In view of the claim that low 25-hydroxyvitamin D (25-OHD) concentrations may contribute to the pathogenesis of bone disease in patients with beta thalassaemia major and iron overload, we have assessed the concentrations of 25-OHD, 1 alpha,25 dihydroxyvitamin D (1 alpha,25(OH)2D), parathyroid hormone, and osteocalcin in such patients. 25-OHD concentrations were significantly lower in patients with thalassaemia major and iron overload than in controls and in some patients were subnormal or undetectable. 1 alpha,25(OH)2D concentrations were, however, normal in all patients and were similar to those in controls. Serum parathyroid hormone and plasma calcium concentrations were also normal and not significantly different from those in controls. Although 25-OHD concentrations increased significantly between January and June, there was no change in 1 alpha,25(OH)2D concentrations. 25-OHD concentrations remained lower than control values, even in June. Parathyroid hormone concentrations fell, but not significantly, between January and June, but calcium concentrations did not alter. Osteocalcin concentrations were normal in all patients except one, who had extremely low concentrations of this protein. The concentration of osteocalcin was not related to 25-OHD or 1 alpha,25(OH)2D concentrations. Thus normal calcium homeostasis is maintained in patients with thalassaemia major despite low or low-normal 25-OHD concentrations; this is probably achieved through the maintenance of normal 1 alpha,25(OH)2D concentrations, which were indistinguishable from those in controls. Normal 1 alpha,25(OH)2D, parathyroid hormone, and osteocalcin concentrations argue against an important role for vitamin D deficiency in the pathogenesis of thalassemia bone disease.     

Bone modulating factors in nephrotic children with normal glomerular filtration rate

Factors influencing bone and mineral metabolism were evaluated in 16 children with active nephrotic syndrome and normal glomerular filtration rate. All patients were proteinuric and/or hypoalbuminemic and had elevated serum triglyceride and cholesterol levels. Seven patients had never received or had discontinued glucocorticoid treatment at least 6 months before the study; six patients were receiving prednisone at the time of study. Although all patients were hypocalcemic (serum total or ionized calcium), none was hypomagnesemic. Despite the low serum calcium levels, circulating immunoreactive parathyroid hormone was elevated in only nine of 16. Plasma 25-hydroxyvitamin D was low in all 16 patients, averaging 7.6 +/- 1.2 ng/mL for the group. In contrast, levels of 1,25-dihydroxyvitamin D were normal in 12 of 14 patients. Bone mineral content measured by photon absorptiometry averaged 83% and was less than 90% of normal in six of nine patients tested. The findings were not influenced by the recent or concurrent administration of glucocorticoid. The data demonstrate abnormalities of mineral and bone modulation in nephrotic children even in the absence of impaired glomerular filtration rate and irrespective of glucocorticoid therapy. The decrease in serum ionized calcium may be related to an absolute deficiency in 25-hydroxyvitamin D and/or a relative deficiency in 1,25-dihydroxyvitamin D. Undermineralization of bone may result from the low levels of vitamin D metabolites and, in some patients, from an increase in immunoreactive parathyroid hormone. Whether treatment with vitamin D metabolites and/or calcium supplementation will prevent the abnormalities remains to be demonstrated.     

Metabolic bone disease of prematurity and secondary hyperparathyroidism

Aim: To illustrate, via case histories, the importance of laboratory investigations for the early diagnosis and management of metabolic bone disease (MBD). Methods: We report three cases of extreme premature infants with MBD. Results: These three infants had several risk factors for MBD of prematurity: very low birthweight, delayed enteral feeds, cholestatic liver disease, intolerance of fortification, the use of glucocorticoids and diuretics. Serum alkaline phosphatase and parathyroid hormone (PTH) were elevated despite relatively normal calcium and phosphate levels. These parameters were corrected with additional supplementation of calcium, phosphate and vitamin D. Conclusions: Infants born extremely prematurely have significant calcium and phosphate depletion by the time they reach full term compared with the normal fetal accretion rate. This is exacerbated if there is poor tolerability to feeds where extra calcium and phosphate could not be added either by additives or via human milk fortifier. Serum calcium and phosphate levels may be normal despite inadequate intake or stores due to the counter‐regulatory effect of PTH. In infants at risk of MBD, testing serum alkaline phosphatase, vitamin D and PTH with calcium and phosphate may assist in the monitoring and management of MBD.     

Congenital hyperparathyroidism and vitamin D deficiency secondary to maternal hypoparathyroidism.

A new case of congenital hyperparathyroidism secondary to maternal hypoparathyroidism is described. Neonatal roentgenograms of the skeleton showed severe bone demineralisation and the distal metaphyses of the long bones were spread, frayed and cupped. Elevated levels of serum immunoreactive parathormone (iPTH) were found at the age of 41 days=270 mulEq/ml (Normal: less than 50 mulEq/ml). A very low plasma 25-OH-D concentration (less than 4 ng/ml) was found at the same time in spite of previous administration of 600 units of vitamin D every day for 18 days and in spite of healing of the bone lesions. At the age of 3 months, 15 mg of vitamin D was given orally: iPTH levels which remained high 3 weeks before (210 mulEq/ml) were found to be normal one week after this vitamin D load (37 mulEq/ml). It is suggested that in congenital hyperparathyroidism secondary to maternal hypoparathyroidism, hyperparathyroidism increases the infants needs for vitamin D. This could result in a state of vitamin D deficiency which in turn would maintain the parathyroid hyperactivity.     

CONGENITAL HYPERPARATHYROIDISM AND VITAMIN D DEFICIENCY SECONDARY TO MATERNAL HYPOPARATHYROIDISM

Abstract. A new case of congenital hyperparathyroidism secondary to maternal hypoparathyroidism is described. Neonatal roentgenograms of the skeleton showed severe bone demineralisation and the distal metaphyses of the long bones were spread, frayed and cupped. Elevated levels of serum immunoreactive parathormone (iPTH) were found at the age of 41 days=270 μlEq/ml (Normal: <50 μlEq/ml). A very low plasma 25-OH-D concentration (<4 ng/ml) was found at the same time in spite of previous administration of 600 units of vitamin D every day for 18 days and in spite of healing of the bone lesions. At the age of 3 months, 15 mg of vitamin D was given orally: iPTH levels which remainded high 3 weeks before (210 μlEq/ml) were found to be normal one week after this vitamin D load (37 μlEq/ml). It is suggested that in congenital hyperparathyroidism secondary to maternal hypoparathyroidism, hyperparathyroidism increases the infants needs for vitamin D. This could result in a state of vitamin D deficiency which in turn would maintain the parathyroid hyperactivity.     

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.     

Hyperparathyroidism

Hyperparathyroidism is a disease characterized by hypercalcemia with hypophosphoremia resulting from increased secretion of parathyroid hormone (PTH). The disease may be divided into 3 forms: a) primary, b) secondary, c) tertiary (secondary refractory form). Primary hyperparathyroidism is rare in children; hyperplasia is more frequent during the early years of life (neonates and infants) and is difficult to distinguish from adenoma in children. The disease may be asymptomatic; elevated calcemia levels (>12 <13.5 mg/dl) are accompanied by anorexia, asthenia and persistent stipsis; severely elevated concentrations (>13.5 mg/dl) are accompanied by nausea, vomiting, polyuria due to osmosis, with dehydration and progressive onset of lethargy, stupor and coma. Osteopenia or osteitis fibrosa cystica may be present due to augmented bone resorption. Height and weight increases are altered due to anorexia and dehydration. Differential diagnosis includes iatrogenic causes of hypercalcemia (excessive vitamin D intake, prolonged immobilization, etc.) and idiopathic familial hypercalcemia. Emergency treatment is required in cases of extremely elevated hypercalcemia (Ca >13.5-14 mg/dl), due to risk of injury to the heart, the central nervous system, the gastrointestinal tract and the kidneys. The 4 cardinal points of treatment are: hydration, calciuresis, inhibition of bone calcium resorption, treatment of the cause underlying hyperparathyroidism. Secondary hyperparathyroidism is found in cases where chronic hypocalcemia is present, particularly in chronic renal failure, untreated deficiency rickets, chronic intestinal malabsorption, hepatobiliary disease, types I and II vitamin D-dependent rickets, tubular acidosis or Fanconi's syndrome. The tertiary form is distinguished by the autonomous nature of the parathyroid glands which have become hypertrophic/hyperplastic due to uncontrollable, chronic severe renal failure. It can also be of iatrogenic origin due to excessive intake of inorganic phosphates in familial hypophosphatemic rickets or chronic vitamin D deficiency.     

Parathyroid function in different stages of vitamin D deficiency rickets

Direct measurements of parathyroid activity are available in only small numbers of children with vitamin D deficiency rickets (VDR). Therefore serum immunoreactive parathyroid hormone (iPTH) and the urinary cyclic adenosine-3,5-monophosphate excretion (UcAMP) were measured together with other important indices of calcium metabolism in 24 patients (aged 2–42 months) with VDR before vitamin D treatment. iPTH and UcAMP were significantly elevated in comparison to age-matched controls. In patients there was a highly significant positive correlation between iPTH and UcAMP and a negative relationship between both indices of parathyroid activity to serum phosphate and urine calcium, respectively, indicating that the simple measurement of serum phosphate and/or urine cAMP and Ca provides a reliable tool for the assessment of secondary hyperparathyroidism in VDR. In two patients classified as being in the early stage of VDR the parathyroid activity was not elevated despite hypocalcemia indicating relative hypoparathyroidism.Twelve patients with VDR were followed during vitamin D therapy: Within the first 2 weeks of treatment UcAMP slightly increased and thereafter decreased in most patients, but was still elevated in three patients even after 7 weeks, whereas iPTH became normal within 3 weeks of treatment. This favors the concept that vitamin D deficiency diminishes the activation of renal adenylate cyclase by PTH which is overcome by the highly increased PTH secretion in the advanced stages of rickets.The basal and calcium-stimulated serum calcitonin (CT) levels, determined in some of the patients, were normal, ruling out a significant disturbance of CT secretion in VDR.Dedicated to Prof. Dr. H. Bickel on the occasion of his 65th birthday     

Calcium and vitamin D metabolism in children with nephrotic syndrome

Although abnormalities of calcium and vitamin D metabolism are recognized in children with nephrotic syndrome, longitudinal observations are not available in these patients during periods of relapse and remission. We report observations in 58 children (mean age 10.1 years) with nephrotic syndrome and normal glomerular filtration rate. Hypocalcemia, modest hyperparathyroidism, and strikingly low calcidiol levels were identified during episodes of relapse. Most alterations were transient, and normalized on remission. The plasma concentration of calcitriol, the most active metabolite of vitamin D, was found to be normal in both relapse and remission. In the presence of hypocalcemia and hyperparathyroidism, however, normal plasma calcitriol levels in relapse may be inappropriately low and reflect a state of relative deficiency. Concurrent glucocorticoid therapy did not modify the results. A corollary of our observations is that children with relapsing or protracted nephrotic syndrome are at risk of developing metabolic bone disease, even without impairment of glomerular filtration rate.