Pediatric reference values for calcium, magnesium and inorganic phosphorus in serum obtained from Bhattacharya plots for data from unselected patients

Chest configuration in children and adolescents with infantile nephropathic cystinosis compared with other chronic kidney disease entities and its clinical determinants

BACKGROUND

Infantile nephropathic cystinosis (INC) is a systemic lysosomal storage disease causing intracellular cystine accumulation, resulting in renal Fanconi syndrome, progressive kidney disease (CKD), rickets, malnutrition, and myopathy. An INC-specific disproportionately diminished trunk length compared to leg length poses questions regarding the functionality of the trunk.

METHODS

Thus, we prospectively investigated thoracic dimensions and proportions, as well as their clinical determinants in 44 pediatric patients with INC with CKD stages 1-5 and 97 age-matched patients with CKD of other etiology between the ages of 2-17 years. A total of 92 and 221 annual measurements of patients with INC and CKD, respectively, were performed, and associations between anthropometric and clinical parameters were assessed using linear mixed-effects models.

RESULTS

Patients with INC exhibited altered chest dimensions that were distinct from CKD controls, characterized by markedly increased chest depth to height and chest depth to chest width ratio z-scores (> 1.0), while those of patients with CKD were only mildly affected (z-score within ± 1.0). Ratio z-scores differed significantly between both patient groups from 2-6 years of age onward. The degree of chest disproportion in INC patients was significantly associated with both the degree of CKD and tubular dysfunction (e.g., low serum phosphate and bicarbonate) across three different age groups (2-6, 7-12, and 13-17 years).

CONCLUSION

Our data show an INC-specific alteration in thoracic shape from early childhood onward, which is distinct from CKD of other etiologies, suggesting early childhood subclinical changes of the musculoskeletal unit of the thoracic cage, which are associated with kidney function. A higher resolution version of the Graphical abstract is available as Supplementary information.

Heterogeneity is a common ground in familial hypomagnesemia with hypercalciuria and nephrocalcinosis caused by CLDN19 gene mutations

BACKGROUND

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare tubulopathy caused by mutations in the CLDN16 or CLDN19 genes. Patients usually develop hypomagnesemia, hypercalciuria, nephrocalcinosis and renal failure early in life. Patients with CLDN19 mutations may also have ocular abnormalities. Despite clinical variability, factors associated with kidney function impairment, especially in patients with CLDN19 mutations, have not been addressed.

METHODS

Retrospective multicenter study of 30 genetically confirmed FHHNC Spanish patients. We analyzed kidney function impairment considering as outcomes chronic kidney disease (CKD) stage 3 and annual estimated glomerular filtration rate (eGFR) decline, to identify factors associated with the different phenotypes.

RESULTS

Of thirty patients, 27 had mutations in the CLDN19 gene (20 homozygous for the p.G20D mutation) and 3 in the CLDN16. Age at diagnosis was 1.71 (0.67-6.04) years and follow-up time was 8.34 ± 4.30 years. No differences in CKD stage 3-free survival based on CLDN19 mutation (p.G20D homozygous vs. other mutations) or gender were found, although females seemed to progress faster than males. Patients with more pronounced eGFR decline had higher PTH levels at diagnosis than those with stable kidney function, despite similar initial eGFR. Approximately 60% of CLDN19 patients presented ocular abnormalities. Furthermore, we confirmed high phenotypic intrafamilial variability.

CONCLUSIONS

In a contemporary cohort of FHHNC patients with CLDN19 mutations, females seemed to progress to CKD-stage 3 faster than males. Increased PTH levels at baseline may indicate a more severe renal course. There was high phenotype variability among patients with CLDN19 mutations and kidney function impairment  differed even between siblings.

Serum alkaline phosphatase relates to cardiovascular risk markers in children with high calcium-phosphorus product

Although alkaline phosphatase (ALP) correlates with cardiovascular risk in adults, there are no studies in children. We evaluated the association between serum ALP levels, calcium-phosphorus product (Ca*P) and cardiovascular risk markers in healthy children. Children aged 7.9 ± 1.4 (n = 379) were recruited in this cross-sectional study. The main outcome measures were systolic and diastolic blood pressure (SBP and DBP) and carotid intima-media thickness (cIMT). Additional assessments were body-mass index (BMI), waist circumference, homeostatic model assessment of insulin resistance (HOMA-IR) and fasting lipids, ALP, serum calcium, phosphorus and Ca*P. ALP was directly correlated with BMI (p < 0.0001), waist circumference (p < 0.0001), SBP (p < 0.0001), cIMT (p = 0.005), HOMA-IR (p < 0.0001), and fasting triglycerides (p = 0.0001). Among them, in children with Ca*P values above the median the associations were BMI (r = 0.231; p = 0.001), waist (r = 0.252; p < 0.0001), SBP (r = 0.324; p < 0.0001), cIMT (r = 0.248; p = 0.001) and HOMA-IR (r = 0.291; p < 0.0001)]. ALP independently associated with SBP (β = 0.290, p < 0.001) and cIMT (β = 0.179, p = 0.013) in children with higher Ca*P, after adjusting for confounding variables. Circulating ALP is associated with a more adverse cardiovascular profile in children with higher Ca*P. We suggest that serum ALP and Ca*P levels could contribute to the assessment of risk for cardiovascular disease in children.

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is a multilineage somatic mosaic RASopathy

BACKGROUND

We recently demonstrated multilineage somatic mosaicism in cutaneous skeletal hypophosphatemia syndrome (CSHS), which features epidermal or melanocytic nevi, elevated fibroblast growth factor (FGF)-23, and hypophosphatemia, finding identical RAS mutations in affected skin and bone.

OBJECTIVE

We sought to: (1) provide an updated overview of CSHS; (2) review its pathobiology; (3) present a new patient with CSHS; and (4) discuss treatment modalities.

METHODS

We searched PubMed for "nevus AND rickets," and "nevus AND hypophosphatemia," identifying cases of nevi with hypophosphatemic rickets or elevated serum FGF-23. For our additional patient with CSHS, we performed histopathologic and radiographic surveys of skin and skeletal lesions, respectively. Sequencing was performed for HRAS, KRAS, and NRAS to determine causative mutations.

RESULTS

Our new case harbored somatic activating HRAS p.G13 R mutation in affected tissue, consistent with previous findings. Although the mechanism of FGF-23 dysregulation is unknown in CSHS, interaction between FGF and MAPK pathways may provide insight into pathobiology. Anti-FGF-23 antibody KRN-23 may be useful in managing CSHS.

LIMITATIONS

Multilineage RAS mutation in CSHS was recently identified; further studies on mechanism are unavailable.

CONCLUSION

Patients with nevi in association with skeletal disease should be evaluated for serum phosphate and FGF-23. Further studies investigating the role of RAS in FGF-23 regulation are needed.