Sphingomyelin and Medullary Sponge Kidney Disease: A Biological Link Identified by Omics Approach

Background: Molecular biology has recently added new insights into the comprehension of the physiopathology of the medullary sponge kidney disease (MSK), a rare kidney malformation featuring nephrocalcinosis and recurrent renal stones. Pathogenesis and metabolic alterations associated to this disorder have been only partially elucidated.Methods: Plasma and urine samples were collected from 15 MSK patients and 15 controls affected by idiopathic calcium nephrolithiasis (ICN). Plasma metabolomic profile of 7 MSK and 8 ICN patients was performed by liquid chromatography combined with electrospray ionization tandem mass spectrometry (UHPLC–ESI-MS/MS). Subsequently, we reinterrogated proteomic raw data previously obtained from urinary microvesicles of MSK and ICN focusing on proteins associated with sphingomyelin metabolism. Omics results were validated by ELISA in the entire patients' cohort.Results: Thirteen metabolites were able to discriminate MSK from ICN (7 increased and 6 decreased in MSK vs. ICN). Sphingomyelin reached the top level of discrimination between the two study groups (FC: −1.8, p < 0.001). Ectonucleotide pyrophophatase phosphodiesterase 6 (ENPP6) and osteopontin (SPP1) resulted the most significant deregulated urinary proteins in MSK vs. ICN (p < 0.001). ENPP6 resulted up-regulated also in plasma of MSK by ELISA.Conclusion: Our data revealed a specific high-throughput metabolomics signature of MSK and indicated a pivotal biological role of sphingomyelin in this disease.

Primary Hyperaldosteronism and Renal Medullary Nephrocalcinosis: A Controversial Association

Primary hyperaldosteronism (PA) is a common disease with a prevalence of 5–10% in unselected patients with hypertension. Medullary nephrocalcinosis is a radiological diagnosis and refers to diffuse calcification in the renal parenchyma. The three commonest causes of nephrocalcinosis are hyperparathyroidism, distal renal tubular acidosis, and medullary sponge kidney. PA is not a recognized cause of nephrocalcinosis. There are a few case reports linking PA with nephrocalcinosis published till date. In this case series, we report three cases where PA was possibly associated with medullary nephrocalcinosis. In all three cases, the common causes of nephrocalcinosis were excluded by careful clinical history, biochemical evaluation, and radiological findings. We conclude and emphasize that a diagnosis of PA as an etiology of medullary nephrocalcinosis should be sought after common causes have been excluded, at least in those with hypertension that is difficult to control.

Hypervitaminosis A: A Rare Cause of Hypercalcemia

Introduction: Hypercalcemia is a rather common clinical problem and a majority of cases are found to be secondary to primary hyperparathyroidism and malignancy. A rare cause of hypercalcemia is associated with high levels of vitamin A and thought to be secondary to the effect of vitamin A on bone to stimulate osteoclastic resorption or inhibit osteoblastic formation. Clinical Case: A 54 year-old male with a past medical history of CKD stage 3 secondary to medullary sponge kidney presented for hypercalcemia. He complained of chronic constipation, joint pain, mood changes and recurrent kidney stones. Reported multivitamin use (including 1000mcg of vitamin A) for years but was discontinued one year prior to visit. Lab work showed calcium of 11.5 mg/dL (8.7–10.2mg/dL), albumin 4.9 g/dL (3.8–4.9g/dL), elevated 24h urine calcium, eGFR 40 mL/min/1.73, parathyroid hormone 5 pg/mL (15-65pg/mL,) normal 1,25-OH vit D and 25-OH vit D, PTHrP <2.0 pmol/L, serum protein electrophoresis unremarkable. His vitamin A level was elevated to 103 ug/dL (20.1–62.0ug/dL). CT chest showed no findings concerning for sarcoidosis. Bone density scan showed normal bone mineral density. Patient diagnosed with hypercalcemia secondary to elevated vitamin A levels. Current limited literature shows stopping the vitamin A supplement will normalize vitamin A levels and correct the hypercalcemia. This patient had discontinued his multivitamin 1 year prior and vitamin A remained elevated, thought to be due to his poor kidney function. Treatment was targeted at improving his hypercalcemia and reducing his symptoms. He was prescribed a one-week course of prednisone 40 mg daily. His calcium level improved to 10.5 mg/dL. Prednisone was reduced to 20 mg daily with normalization of calcium to 10.3 mg/dL (8.7–10.2mg/dL). Conclusion: Hypercalcemia is a rare but known complication of vitamin D toxicity. The liver, kidney and adrenal glands store vitamin A and it is excreted in the urine. Liver and kidney disease pose higher risk of vitamin A toxicity. We present a unique case of Hypercalcemia secondary to elevated vitamin A levels in a patient with moderate chronic kidney disease who was not taking excessive amounts of vitamin A and whose calcium and vitamin A did not normalize once vitamin A supplements were discontinued. The CKD 3 may have reduced vitamin A clearance and increased its toxicity. Hypercalcemia is not the only concern regarding vitamin A toxicity, the increasing use of dietary supplements and over the counter medications may pose significant risks for osteoporosis and bone fractures. A high clinical suspicion and thorough workup to exclude other causes of hypercalcemia is warranted to diagnose hypervitaminosis A as the etiology. Steroids can reduce gastrointestinal absorption of calcium, however, its role in vitamin A toxicity remains unclear. Further research is needed to investigate the appropriate treatment for these patients.