Renal calcification in the first year of life

Mild infantile hypercalcemia: diagnostic tests and outcomes

OBJECTIVE

To assess outcome in a cohort of patients with infantile hypercalcemia followed over 3 years.

STUDY DESIGN

Patients (n = 32) presenting to the calcium clinic between July 2002 and September 2008 were studied. In addition to tests of calcium phosphate metabolism, serum insulin-like growth factor-1, calcitonin, urine citrate, and calcium-sensing receptor gene analysis were obtained.

RESULTS

Mean age at presentation was 6.0 ± 6.3 months. Mean calcium level was 11.4 ± 0.7 mg/dL (2.84 ± 0.17 mmol/L). A recognized cause was found in 14% and a probable cause in 14% of the cohort. Those with nephrocalcinosis (n = 11) had significantly lower mean weight SDS and higher mean calcium levels. The biochemical profile of those in whom no cause could be determined included nonsuppressed parathyroid hormone with either normal or increased 1,25(OH)(2)D. Hypercalcemia resolved in 20 patients. However, in approximately a third, there was persistence in hypercalcemia, hypercalciuria, or nephrocalcinosis.

CONCLUSIONS

The addition of 1,25(OH)(2)D and calcium-sensing receptor mutation analysis to a panel of investigations may improve diagnostic yield. Clinical outcome is overall good, however, one-third need ongoing follow-up.

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.

Long-term follow-up of patients with idiopathic infantile hypercalcaemia

Idiopathic infantile hypercalcaemia (IIH) is a rare disorder of unknown etiology that presents with hypercalcaemia in a child's first year of life. There is only a limited number of published reports of the natural history of this condition, and the long-term prognosis is largely unknown. The presentation, treatment and long-term follow-up of 11 children with IIH treated at our institution since 1993 are described. Hypercalcaemia resolved in the majority of children by the time they were 3 years of age, but nephrocalcinosis and persistent hypercalciuria were common, and, in some cases, urinary calcium excretion increased after initially becoming normal. This study suggests that clinical and biochemical abnormalities may persist for longer than previously reported and implies the need for ongoing surveillance of patients with IIH.

Resolution of medullary nephrocalcinosis in children with metabolic bone disorders

Ultrasonographic resolution of nephrocalcinosis (NC) has been reported in children with furosemide-induced NC, but not in other entities. We report the cases of four children with metabolic bone disease, two with hypophosphatasia and two with X-linked hypophosphatemic rickets, in whom we observed resolution of renal calcifications. At the time of ultrasonographic resolution of NC, 3 of the patients were on anticalciuric diuretics, and all 4 had normal urinalysis, serum creatinine and electrolyte profiles, as well as estimated creatinine clearance. In 3 of the children, evidence of mild tubular dysfunction was found. It thus seems that in some children with bone and mineral disorders who develop NC, ultrasonographic resolution of the renal calcifications can be seen; however, mild tubular dysfunction may remain and require follow-up. Further studies are suggested to explore the possible role of anticalciuric diuretics in promoting the resolution of NC.

Neonatal nephrocalcinosis in association with glucose-galactose malabsorption

We report a case of severe nephrocalcinosis related to hypercalcaemia in a newborn with glucose-galactose malabsorption. He presented with poor growth and was noted to have polyuria, which was later recognised to be severe watery diarrhoea. We discuss the possible aetiological factors for nephrocalcinosis in this condition.

Renal excretion of calcium and phosphorus in premature infants with incipient late metabolic acidosis

BACKGROUND

Premature infants receiving alimentation with cow milk-based formulas run a considerably high risk of incipient late metabolic acidosis, an early stage developing of manifest late metabolic acidosis. Is bone metabolism involved in pathophysiologic mechanisms characterizing this early stage of retention acidosis?

METHODS

Urinary ionography was performed in 10 premature infants with spontaneous development of incipient late metabolic acidosis (indicated by urine pH < 5.4 on 2 consecutive days) and 10 pair-matched premature infants with normal values of urine pH; both groups were receiving full oral nutrition with the same standard formula. Moreover, in 37 premature infants with incipient late metabolic acidosis who were randomly allocated to oral therapy with 2 mmol. kg(-1). d(-1) of either NaHCO 3 or NaCl over a period of 7 days, urinary excretion of calcium and phosphorus was assessed on day 1 and day 7.

RESULTS

Incipient late metabolic acidosis was accompanied by increased phosphaturia in premature infants receiving full oral nutrition. Seventeen premature infants receiving NaCl therapy (19 treatment periods) showed increased calciuria from day 1 to day 7, whereas, in 20 premature infants receiving NaHCO 3 therapy (23 treatment periods), calcium or phosphorus excretion in urine did not increase.

CONCLUSIONS

The data of urinary calcium and phosphorus excretion in premature infants support the hypothesis that bone mineralization may already be impaired in the early stage of incipient late metabolic acidosis.

Renal follow up of premature infants with and without perinatal indomethacin exposure

AIMS

To evaluate early childhood renal growth, structure, and function in children born at less than 33 weeks gestation and to investigate possible independent effects of perinatal indomethacin exposure.

METHODS

A total of 66 children born at less than 33 weeks gestation, 31 of them with perinatal indomethacin exposure (study group) and 35 without (control group), were examined at 2-4 years of age. Serum cystatin C and protein; plasma creatinine, sodium, and potassium; urine protein, calcium:creatinine ratios, and alpha(1) microglobulin; and glomerular filtration rate (GFR) were determined. Renal sonography examinations were performed.

RESULTS

The mean serum cystatin C concentrations were slightly higher in the control group than in the study group. Mean values of serum protein, and plasma creatinine and sodium did not differ between the groups, neither did median plasma potassium concentrations and urine protein:creatinine and calcium:creatinine ratios. None had tubular proteinuria. Abnormal GFR (<89 ml/min/1.73 m(2)) was found in one case in each group and renal structural abnormalities in five in each group. In logistic regression analysis the duration of umbilical artery catheter (UAC) use and furosemide treatment emerged as the significant independent risk factors for renal structural abnormalities. Furosemide treatment and assisted ventilation remained the risk factors associated with renal abnormalities in general-that is, functional and/or structural abnormal findings.

CONCLUSION

Perinatal indomethacin does not seem to affect long term renal growth, structure, or function in children born at less than 33 weeks gestation. Duration of UAC use, furosemide treatment, and assisted ventilation may be correlated with later renal structural and functional abnormalities.

Role of macrophages in nephrolithiasis in rats: an analysis of the renal interstitium

Interstitial calcium oxalate (CaOx) crystals can be found in primary oxalosis and in secondary hyperoxaluria. In a rat model for nephrolithiasis, we investigated whether such crystals can be removed by the surrounding interstitial cells. CaOx crystals were induced by a crystal-inducing diet based on ethylene glycol (EG) and ammonium chloride (CID). Both lithogenic compounds were added to the drinking water. After 9 days, the animals received normal drinking water for 2 days. Using this CID, only the interstitial crystals are retained. Subsequently, half of the population remained on normal drinking water (normo-oxaluria), whereas the other half received a low dose of EG alone (chronic hyperoxaluria). The rats were killed at regular times thereafter. The results showed that the kidney-associated oxalate significantly declined during normo-oxaluria, but remained high during chronic hyperoxaluria. Interstitial cells positive for the leukocyte common antigen (CD45; which identifies all types of leukocytes), the ED1 antigen (which is specific for monocytes and macrophages), and the major histocompatibility class II antigen (MCHII), respectively, had increased in number, with minor differences between both rat populations. The cells around the interstitial crystals were mostly positive for ED1. Multinucleate giant cells were regularly observed. These cells were positive for CD45 and ED1 and sometimes also for MCHII. The crystals in these cells were moderately positive for acid phosphatase and carbonic anhydrase II. It is concluded that interstitial CaOx crystals can be removed under normo-oxaluric conditions and that, in all likelihood, macrophages and multinucleate giant cells are involved in that process.