Oral calcium-loading test in infancy, with particular reference to idiopathic hypercalcaemia

Genetic causes of neonatal and infantile hypercalcaemia

The causes of hypercalcaemia in the neonate and infant are varied, and often distinct from those in older children and adults. Hypercalcaemia presents clinically with a range of symptoms including failure to thrive, poor feeding, constipation, polyuria, irritability, lethargy, seizures and hypotonia. When hypercalcaemia is suspected, an accurate diagnosis will require an evaluation of potential causes (e.g. family history) and assessment for physical features (such as dysmorphology, or subcutaneous fat deposits), as well as biochemical measurements, including total and ionised serum calcium, serum phosphate, creatinine and albumin, intact parathyroid hormone (PTH), vitamin D metabolites and urinary calcium, phosphate and creatinine. The causes of neonatal hypercalcaemia can be classified into high or low PTH disorders. Disorders associated with high serum PTH include neonatal severe hyperparathyroidism, familial hypocalciuric hypercalcaemia and Jansen's metaphyseal chondrodysplasia. Conditions associated with low serum PTH include idiopathic infantile hypercalcaemia, Williams-Beuren syndrome and inborn errors of metabolism, including hypophosphatasia. Maternal hypocalcaemia and dietary factors and several rare endocrine disorders can also influence neonatal serum calcium levels. This review will focus on the common causes of hypercalcaemia in neonates and young infants, considering maternal, dietary, and genetic causes of calcium dysregulation. The clinical presentation and treatment of patients with these disorders will be discussed.

Genetic defect in CYP24A1, the vitamin D 24-hydroxylase gene, in a patient with severe infantile hypercalcemia

CONTEXT

Idiopathic infantile hypercalcemia (IIH) is a disorder the genetic etiology and physiological basis of which are not well understood.

OBJECTIVE

The objective of the study was to describe the underlying physiology and genetic cause of hypercalcemia in an infant with severe IIH and to extend these genetic findings into an additional cohort of children with IIH.

DESIGN

This was an inpatient study of a single patient with consanguineous parents at an academic medical center with follow-up in a specialty clinic cohort.

PATIENTS

The patient population was one patient with severe IIH for gene discovery and physiological testing and 27 patients with idiopathic infantile hypercalcemia in the replication cohort.

INTERVENTIONS

Interventions included a calcium isotopic absorption study as well as homozygosity mapping and whole-exome sequencing in a single patient followed up by gene sequencing in replication cohort.

MAIN OUTCOME MEASURE

Fractional absorption of calcium and genetic variants causing hypercalcemia were measured.

RESULTS

Intestinal calcium absorption was extremely elevated (∼90%). A rare homozygous deletion in the CYP24A1 gene was found, leading to the loss of a single highly conserved amino acid. In vivo functional studies confirmed decreased 24-hydroxylase activity because the subject had undetectable levels of 24,25-dihydroxyvitamin D. No coding variants in CYP24A1 were found in the 27 additional patients with IIH.

CONCLUSIONS

Our study confirms that CYP24A1 plays a causal role in some but not all cases of IIH via markedly increased intestinal absorption of calcium, suggesting that genetic diagnosis could be helpful in a subset of IIH patients. This case demonstrates the power of an unbiased, genome-wide approach accompanied by informative physiological studies to provide new insights into human biology.

Involvement of claudin 3 and claudin 4 in idiopathic infantile hypercalcaemia: a novel hypothesis?

BACKGROUND

Idiopathic infantile hypercalcaemia (IIH) is a rare disease that generally resolves spontaneously between the age of 1 and 3 years. Similar symptoms may occur in patients suffering from Williams-Beuren syndrome (WBS), which is caused by a microdeletion on chromosome 7. Two of the genes, named CLDN3 and CLDN4, located within this region are members of the claudin family that has been shown to be involved in paracellular calcium (Ca(2+)) absorption. Based on the hemizygous loss of CLDN3 and CLDN4 in WBS and the function of these genes in paracellular Ca(2+) transport, we hypothesized that mutations in CLDN3 or CLDN4 could also be involved in IIH.

METHODS

Biochemical characteristics, including calciotropic hormone levels, were obtained from three typical IIH patients. CLDN3 and CLDN4 sequences were also analysed in these patients. The major intestinal Ca(2+) transporter TRPV6 was also screened for the presence of mutations, since hypercalcaemia in IIH and WBS has been shown to result from intestinal hyperabsorption. All three patients were also analysed for the presence of deletions or duplications using a single-nucleotide polymorphism (SNP) array for genomic DNA.

RESULTS

The serum Ca(2+) levels of patients were 2.9, 3.3 and 3.8 mmol/L (normal <2.7 mmol/L). Levels of 25-hydroxyvitamin D(3) and 1,25-dihydroxyvitamin D(3) were normal, parathyroid hormone (PTH) and PTH-related peptide (PTHrP) levels were appropriately low. Sequencing of coding regions and intron-exon boundaries did not reveal mutations in CLDN3, CLDN4 and TRPV6. Identified SNPs were not correlated with the disease phenotype. A SNP array did not reveal genomic deletions or duplications.

CONCLUSIONS

Biochemical analysis did not reveal inappropriate levels of calciotropic hormones in IIH patients in this study. Furthermore, based on the lack of mutations in CLDN3, CLDN4 and TRPV6, we conclude that IIH is neither caused by mutations in these candidate genes nor by deletions or duplications in the genome of these patients.

Williams syndrome: an historical perspective of its evolution, natural history, and etiology

This review examines the Williams syndrome (WS) from an historical perspective, beginning with the early descriptions of idiopathic infantile hypercalcemia (IIH) and ending with some speculative ideas about a possible causative function of a recently discovered neuropeptide. The earliest reports of WS individuals are probably those which describe a "severe" subgroup of IIH and separate it from the epidemic of milder IIH reported in Post-WWII Great Britain and Europe. Most of these latter cases apparently resulted from hypervitaminosis D produced by excessive supplementation of government-supplied infant foods. With more extensive recognition and reporting of this "severe" subgroup, the diagnostic constellation of IIH, mental deficiency, elfin face, and supravalvular aortic stenosis (SVAS) evolved as WS. More of these reports emphasized the physical and behavioral manifestations as the key diagnostic features, and the frequency of occurrence and relative importance of SVAS and IIH in WS decreased. Despite the diminished consequence of hypercalcemia, calcium and vitamin D have continued to dominate the investigation of the cause of infantile hypercalcemia and led to the proposal and confirmation of deficient calcitonin secretion in individuals with WS. Though calcitonin is probably pertinent only to infantile hypercalcemia, its alternative gene product, calcitonin-gene-related product, is an important neuropeptide with physiological effects in the central nervous system and cardiovascular systems which raise the possibility that it may be responsible for some of the manifestations of WS.

Adults with Williams syndrome

Reports of adults with Williams syndrome (WS) have been rare. We have evaluated 13 adult WS patients and reviewed 16 case reports of WS in patients older than age 16 years. Adults in our study had progressive multisystem medical problems. Cardiovascular complications were common (12/13) including hypertension (8), supravalvular aortic stenosis (9), aortic hypoplasia (3), pulmonic artery stenosis (4), peripheral stenoses (3), and mitral valve prolapse (2). Joint limitation (12/13) was progressive, often accompanied by kyphoscoliosis and lordosis. Recurrent urinary tract infections in 6 individuals led to radiologic studies showing urethral stenosis in 2, and bladder diverticula and vesicoureteral reflux in 3. Gastrointestinal problems included obesity (5), chronic constipation (7), diverticulosis (3), and cholelithiasis (4). Hypercalcemia was documented in 5 patients, although others had hypercalcemic symptoms (abdominal pain, polyuria, and constipation). One 45-year-old man had parathyroid hyperplasia. Previous reports likewise document significant morbidity. Thus, Williams syndrome in an adult appears to dictate aggressive evaluation and monitoring. Investigation of calcium metabolism should be undertaken in each adult WS patient.

Idiopathic infantile hypercalcemia discovered in the newborn period

We report a male newborn with typical clinical signs of idiopathic infantile hypercalcemia (IIH); that is, hypercalcemia, hypercalciuria, an elfin face and nephrocalcinosis without giving Vitamin D3 supplementation to the patient. He had been treated with a vitamin D-free, low calcium milk and rectal administration of exogenous calcitonin (elcatonin). The latter seemed to be more effective as a treatment for IIH. The serum calcium level came within the normal range and the serum 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) level decreased from 101.5 to 75.6 pg/mL with the treatments mentioned above. These results suggest that a high serum concentration of 1,25(OH)2D3 is part of the pathogenesis of IIH. However, we were not able to clarify the pathogenesis of the high serum concentration of 1,25(OH)2D3.

Calcium metabolism in Williams-Beuren syndrome

Increased 1,25-dihydroxyvitamin D levels and decreased basal and calcium-stimulated calcitonin serum levels have been found in children with Williams-Beuren syndrome (WBS). To determine whether isolated or combined disturbances of secretion or action of the calcium-regulating hormones may cause the tendency to hypercalcemia in WBS, we investigated several aspects of calcium metabolism in 27 normocalcemic children and adults, aged 2 to 47 years, with WBS. With the exception of slightly decreased 25-hydroxyvitamin D and slightly increased calcitonin in serum, all measured basal indexes of calcium and bone metabolism, including the serum levels of intact parathyroid hormone and 1,25-dihydroxyvitamin D, were comparable to control values. Total and extractable calcitonin, the latter representing the monomeric and biologically important form of the hormone, showed the same relative increase after a low-dose calcium infusion in patients and control subjects, indicating a normal capacity of the calcitonin-producing C cells of the thyroid gland in WBS. Furthermore, exogenous parathyroid hormone induced a normal response of 1,25-dihydroxyvitamin D, cyclic adenosine monophosphate, and phosphate excretion, indicating a normal response of the renal 25-hydroxyvitamin D-1 alpha-hydroxylase and the renal receptor-adenylate cyclase system to parathyroid hormone. These findings suggest that neither deficient calcitonin secretion nor increased renal sensitivity to parathyroid hormone is a feature of WBS in normocalcemic patients.

The calcitonin-CGRP gene in the infantile hypercalcaemia/Williams-Beuren syndrome

We have investigated 13 families, each of which have one member with infantile hypercalcaemia/Williams-Beuren syndrome (IHWBS), for either a germ cell mutation of, or an association with, the calcitonin-CGRP gene. Restriction fragment mapping studies of the calcitonin-CGRP gene using five restriction enzymes (TaqI, Bg/II, PvuII, PstI, and SacI) and region specific probes failed to show any abnormalities of this gene complex. NO association of IHWBS with polymorphism of the calcitonin-CGRP/parathormone locus was found. Therefore, although the aetiology of IHWBS may be caused by a new dominant mutation, there is no evidence to implicate major rearrangements of the calcitonin-CGRP and parathormone genes.

Progressive vascular lesions in Williams-Beuren syndrome

We report two patients with Williams-Beuren syndrome. The first patient showed no evidence of coarctation of the aorta at the first examination. Seven years later, she developed coarctation of the aorta. In the second patient, we found the progression of renal artery stenosis by serial angiography. We report that vascular lesions may be progressive in Williams-Beuren syndrome.

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.

Infantile hypercalcemia with subcutaneous fat necrosis. Report of a case with studies on the pathogenesis of hypercalcemia

A case of hypercalcemia in neonatal subcutaneous fat necrosis, which was successfully treated with a low Ca and vitamin D-free formula, is described. Low 1,25(OH)2D and severe calciuria, which were considered to result from hypercalcemia itself as well as parathyroid suppression, were noted during the hypercalcemic phase. The oral Ca load test was repeatedly normal, suggesting that intestinal hyperabsorption of Ca was not a cause of the hypercalcemia. Later recurrence of calciuria without hypercalcemia was noted concomitant with softening of indurated calcified necrotic tissue. In this patient, cerebral infarction on the left side was detected by CT scanning.

Williams syndrome

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Imparied calcitonin secretion in patients with Williams syndrome

Williams syndrome is associated with neonatal hypercalcemia of unclear pathogenesis. To learn more about the hormonal control of calcium metabolism in patients with Williams syndrome, we studied five such children, with intravenous calcium and parathyroid hormone infusions as provocative stimuli. These patients were found to have significantly higher mean baseline calcium concentrations, delayed clearance of calcium after intravenous calcium loading, and blunted calcitonin responses after calcium infusion, compared with a group of seven normal children. No abnormalities of vitamin D metabolite concentrations were found, either before or after parathyroid hormone stimulation. Our studies demonstrate that patients with Williams syndrome have a defect in the synthesis or release of immunoreactive calcitonin. A deficiency of calcitonin may explain the abnormalities of calcium metabolism seen in these patients and can serve as an important endocrine marker for Williams syndrome.

Idiopathic infantile hypercalcaemia--a continuing enigma

Seventy six children with documented Fanconi-type idiopathic infantile hypercalcaemia were studied and compared with 41 with the Williams-Beuren syndrome. Clinical comparison showed, as expected, very close similarities but also considerable differences, particularly in the severity of feeding problems and the degree of failure to thrive. The estimated incidence of idiopathic infantile hypercalcaemia alone has remained constant for the past 20 years, at approximately 18 cases per year in the United Kingdom (1 per 47 000 total live births). Long term morbidity in these children is mainly due to mental handicap and arteriopathy, but hypertension (29%), kyphoscoliosis (19%), hyperacusis (75%), and obesity (50%) may be added complications. In one child, hypercalcaemia recurred during adolescence but this seems to be excessively rare. More detailed investigation before treatment is required to discover the aetiology of hypercalcaemia in this condition.

Supravalvular aortic stenosis with parafollicular cell (C-cell) hyperplasia

Autopsy examination of a patient with well-documented supravalvular aortic stenosis and other characteristic features of the idiopathic infantile hypercalcemia syndrome revealed previously unreported hyperplasia of parafollicular cells (C cells). Immunohistochemical analysis demonstrated up to 30 calcitonin-containing cells per high power field, whereas normal glands contain only 4 to 10 cells per low power field in areas of highest concentration. The parathyroid glands were found to be normal both grossly and microscopically, whereas the bones showed thickened trabeculas, normal Haversian canals and no apparent increase in osteoblast or osteoclast activity, suggesting normal parathyroid hormone, but increased thyrocalcitonin activity. We suggest that C-cell hyperplasia has occurred in response to a persistent, rather than transient, elevation in serum calcium levels and that thyrocalcitonin function is augmented, rather than impaired in this disorder. The primary biochemical defect promoting hypercalcemia remains to be clarified, as well as the role, if any, such a defect plays in producing significant pathology in the central nervous system and in the cardiovascular, renal and skeletal systems.

Renal tubular and papillary necrosis after dehydration in infancy

Two infants are described who developed renal tubular and papillary necrosis. In one, severe problems of management occurred during the diuretic phase. In the other, the intravenous pyelogram showed characteristic changes during the acute illness. The urinary findings are compared with those in other dehydrated infants and a means of early diagnosis is suggested. In a dehydrated infant an initial urine sodium of more than 100 mEq/l., the persistence of osmolality below 500 mOsm/kg, and urea below 1500 mg/100 ml suggest renal tubular damage.

Diencephalic syndrome of infantile emaciation. Analysis of literature and report of further 3 cases

Three children with diencephalic tumours are described, and an analysis of 45 cases from the literature together with our own 3 is presented. Boys are affected more frequently than girls (1·8:1) and the onset is during the first 12 months of life in 92% of cases. The main clinical features are emaciation, overactivity, pleasant disposition, and above-average height. The natural course of the disease is variable. Treatment is by radiotherapy. Operative intervention, except to relieve intracranial hypertension, is not usually indicated.

Oral calcium-loading test in rickets and in neonatal tetany: effect of vitamin D

In an oral calcium-loading test performed on 10 infants with vitamin-D deficiency rickets and low fasting calcium levels, a comparison of results before and after therapy showed that vitamin D raised the serum calcium level at each stage of the test and altered the response so that a more rapid and substantial rise and fall in serum calcium occurred.The effects of vitamin D therapy on newborn infants with hypocalcaemic hyperphosphataemic tetany in another study suggests that these infants should be treated in this way to make them more responsive to oral calcium therapy.