Diagnostic strategy for inherited hypomagnesemia.

BACKGROUND: Hereditary hypomagnesemia is difficult to diagnose accurately because of its rarity and the variety of causative genes. We established a flowchart for identifying responsible genes for hypomagnesemia, and we confirmed its diagnostic efficacy in patients with suspected inherited hypomagnesemia. METHODS: We established a flowchart and applied it to five index cases with suspected inherited hypomagnesemia. Direct sequence analysis was used to detect the causative gene variants in four cases, and targeted sequencing analysis using next-generation sequencing (NGS) of all causative genes for hypomagnesemia was used in one. RESULTS: Expected pathogenic variants were detected in the HNF1B, TRPM6, CLDN16, CASR, or SLC12A3 gene in all five cases. The results of all genetic analyses were consistent with the clinical diagnostic results using the flowchart. CONCLUSIONS: Accurate genetic diagnosis is crucial for estimating the prognosis, detecting complications in organs other than the kidneys, and for directing genetic counseling. The developed flowchart for identifying responsible genes for hypomagnesemia was useful for diagnosing inherited hypomagnesemia. In addition, NGS analysis will help to resolve clinical difficulties in making an accurate diagnosis and thus improve the diagnostic strategy for inherited hypomagnesemia.

Pathogenesis of hypokalemia in autosomal dominant hypocalcemia type 1.

BACKGROUND: Autosomal dominant hypocalcemia type 1 (ADH1) is a relatively rare endocrine disorder characterized by hypocalcemia and inadequate parathyroid hormone secretion. ADH is caused by activating mutations in the calcium-sensing receptor (CaSR) gene, CASR. CaSR plays a crucial role in calcium and magnesium homeostasis in the kidney. ADH may be accompanied by hypokalemia and metabolic alkalosis when it is classified as type V Bartter syndrome. However, the mechanism underlying hypokalemia in this disease is unclear. METHODS: We investigated a 33-year-old woman with hypocalcemia and hypoparathyroidism since childhood, whose mother also had hypocalcemia and hypoparathyroidism, but with no clinical symptoms. Blood examinations showed hypokalemia and metabolic alkalosis in the patient, but not her mother. We conducted mutation analysis and diuretic tests to clarify the patient's and her mother's diagnosis and to investigate the onset mechanism of hypokalemia in ADH1. We also determined the localization of CaSR in the kidney by immunohistochemistry. RESULTS: We detected a known gain-of-function mutation in CASR in both the patient and her mother. Diuretic tests revealed a response to furosemide and no reaction to thiazide in the patient, although the mother responded well to both diuretics. CaSR co-localized with the Na(+)-Cl(-) cotransporter (NCCT) on distal tubular epithelial cells. CONCLUSIONS: These results indicate that the NCCT in the distal convoluted tubule was secondarily affected in this patient. We conclude that the main pathogenesis of secondary hypokalemia in ADH1 in this patient was secondary NCCT dysfunction.

Two cases of ceftriaxone-induced encephalopathy treated by hemoperfusion in hemodialysis patients.

Ceftriaxone is a third-generation cephalosporin commonly used to treat infection. However, encephalopathy is an emerging adverse effect of ceftriaxone infusion. These patients present with various symptoms, including those of neurotoxicity, that typically resolve 1 week after discontinuation of ceftriaxone. We experienced two cases of ceftriaxone-induced encephalopathy that were successfully treated by rapid removal of ceftriaxone by hemoperfusion.

Lipid droplet-associated proteins protect renal tubular cells from fatty acid-induced apoptosis.

Proteinuria is a major cause of tubulointerstitial kidney damage, and free fatty acids bound to albumin are thought to play an important role in its pathogenesis. However, the mechanism whereby proteinuria causes tubulointerstitial damage to the kidney is unclear. Using primary human renal proximal tubular cells, we observed that albumin replete with fatty acids (rBSA) and defatted albumin (dBSA) complexed with linoleic acid (LA) induced significantly more apoptosis than did defatted albumin alone. Oxidative stress was partially involved in apoptotic induction by LA/dBSA but not by rBSA. Administration of fatty acid-bound BSA increased the number of lipid droplets (LDs) and the LD-associated proteins, adipocyte differentiation-related protein and TIP47. LDs are organelles that store esterified fatty acids, and the LD-associated proteins are presumed to facilitate LD formation. Knockdown of adipocyte differentiation-related protein or TIP47 by RNA interference enhanced induction of apoptosis by both rBSA and LA/dBSA. Apoptotic induction was observed similarly when either rBSA or LA/dBSA was applied to only the apical surfaces of polarized LLC-PK1 cells. The present results suggest that LDs and LD-associated proteins have protective effects against apoptosis induced by fatty acid-bound albumin by sequestering free fatty acids. Therapeutic manipulation of these LD-associated proteins could aid in the amelioration of nephritic diseases.

[Case of thrombotic thrombocytopenic purpura with a positive Coomb test].

We report a case of thrombotic thrombocytopenic purpura (TTP) with a positive Coombs' test. A 59-year-old female was admitted to our hospital in February, 1997 with symptoms of heart failure. Ultrasound cardiography showed moderate pericardiac effusion and she was diagnosed as having pericarditis. After admission she had anorexia and her urine volume was reduced. Laboratory tests showed anemia and thrombocytopenia. Her Coombs' test result was positive. Her renal function gradually worsened and her conscious level was reduced. We diagnosed her as TTP and judged that she needed hemodialysis. We performed plasma exchange and started steroid therapy. The renal biopsy was compatible with TTP. After treatment, her level of consciousness improved, but her renal function did not improve. On the 51st hospital day she fell into acute respiratory distress syndrome (ARDS) and entered ICU. We considered ARDS caused by infection and continued treatment, but she died of shock and lactate acidosis. Activity of von Willebrand factor-cleaving protease in our case was 15% before the first PE, and 25 % just before death. A case of TTP without collagen disease usually shows a negative Coombs' test result. We think that this was a rare case in which autoimmune hemolytic anemia was supervened with TTP.