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Gitelman syndrome is an autosomal recessive genetic disease caused by pathogenic variants in SLC12A3 resulting in the loss of function of the Na–Cl co-transporter (NCC) in the distal tubules. Hypokalemia and diuretic effects can cause secondary type 2 diabetes and renal function decline. Here, we present the case of a 49-year-old male patient with chronic persistent treatment-resistant hypokalemia for the past 13 years who had been receiving treatment for type 2 diabetes mellitus for 6 years. He was referred to our department due to the presence of urinary protein, impaired renal function, high renin activity, and hyperaldosteronism. Laboratory test results showed hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis. Using next-generation and Sanger sequencing, we identified a novel stop-gain variant (NM_000339.3:c.137del [p.His47fs]) and a missense variant (NM_000339.3:c.2927C > T [p.Ser976Phe]) in the SLC12A3 gene. This novel pathogenic variant was located at the intracellular N-terminus of the NCC. Based on these findings, the patient was diagnosed with Gitelman syndrome. The use of next-generation sequencing facilitated the exclusion of diseases with similar clinical symptoms.

Infiltration by IgG-positive plasma cells is a common finding in tubulointerstitial nephritis. Indeed, it has been thought that CD138-positive mature plasma cells secrete mainly IgG, and the occurrence of tubulointerstitial nephritis with CD138-positive plasma cells secreting IgM has rarely been reported. Routine immunofluorescence of fresh frozen sections is considered the gold standard for detection of immune deposits. However, the immunoenzyme method with formalin-fixed, paraffin-embedded sections is superior for detecting IgM- or IgG-positive cells within the renal interstitium, thus histologic variants may often go undetected. We recently discovered a case of tubulointerstitial nephritis showing IgM-positive plasma cell accumulation within the interstitium. To further explore the morphologic and clinical features of such cases, we performed a nationwide search for patients with biopsy-proven tubulointerstitial nephritis and high serum IgM levels. We identified 13 patients with tubulointerstitial nephritis and IgM-positive plasma cell infiltration confirmed with the immunoenzyme method. The clinical findings for these patients included a high prevalence of distal renal tubular acidosis (100%), Fanconi syndrome (92%), and anti-mitochondrial antibodies (82%). The pathologic findings were interstitial nephritis with diffusely distributed CD3-positive T lymphocytes and colocalized IgM-positive plasma cells, as well as tubulitis with CD3-positive T lymphocytes in the proximal tubules and collecting ducts. Additionally, levels of H+-ATPase, H+, K+-ATPase, and the HCO3−-Cl− anion exchanger were markedly decreased in the collecting ducts. We propose to designate this group of cases, which have a common histologic and clinical form, as IgM-positive plasma cell–tubulointerstitial nephritis.

Methotrexate (MTX) has been documented to accumulate in "third spaces'' such as pleural effusions or ascitic fluids, resulting in delayed clearance and severe toxicity. We present a case of Burkitt lymphoma possessing large liver cysts, up to the size of 7 x 7 cm, wherein clearance of high-dose MTX was severely delayed, despite normal renal and liver functions. The serum MTX concentration was higher than 0.1 microM on day 12 and remained at toxic levels, higher than 0.01 microM, even on day 25, resulting in severe neutropenia, anorexia, and diarrhea. It was presumed that MTX accumulated in the liver cysts over time and was slowly released back into the serum, resulting into prolonged high serum MTX concentrations. High dose of MTX in patients with large liver cysts induces severe toxicity by virtue of MTX accumulation in the cysts and its subsequent delayed clearance.

S-1 and cisplatin are used as one of the first-line chemotherapies for gastric cancer in Japan. The plasma concentration of 5-fluorouracil (5-FU) is increased in patients with renal dysfunction because gimeracil in S-1 inhibits the degradation of 5-FU and about 50% of gimeracil is excreted in the urine. We describe a 35-year-old man with acute kidney injury while taking S-1 and cisplatin for advanced gastric cancer and who presented severe adverse effects of 5-FU. This case report describes the evolution of the plasma concentrations of 5-FU with haemodialysis along with a decrease in the adverse drug effects.

Renal interstitial fibrosis is the common pathway in progressive renal diseases, where oxidative stress promotes inflammation and macrophage infiltration. Febuxostat is a novel nonpurine xanthine oxidase (XO)-specific inhibitor for treating hyperuricemia. While some reports suggest a relationship between hyperuricemia and chronic kidney disease (CKD), the renoprotective mechanism of an XO inhibitor in CKD remains unknown. Recent reports have focused on XO as a source of oxidative stress.Here, we investigate the potential of febuxostat to reduce fibrogenic and inflammatory responses in an established interstitial fibrosis model-unilateral ureteric obstruction (UUO). Male Sprague-Dawley rats were divided into three groups: sham-operated group, vehicle-treated UUO group, and febuxostat-treated UUO group.Treatment with febuxostat diminished XO activity in obstructed kidneys, and suppressed nitrotyrosine, a marker of oxidative stress. Consequently, febuxostat inhibited early proinflammatory cytokine expression, followed by a reduction of interstitial macrophage infiltration. In addition, febuxostat suppressed transforming growth factor-β messenger RNA expression, thereby ameliorating smooth muscle alpha actin and type I collagen expression.Our results provide evidence for the renoprotective action of febuxostat against the formation of interstitial fibrosis. A decrease in macrophage infiltration and interstitial fibrosis, along with a decrease of the oxidative stress marker, strongly suggests the existence of a causal relationship between them. Febuxostat may have therapeutic value in slowing or preventing interstitial fibrosis in patients with CKD.

Sir—A number of chronic kidney disease patients with diabetes receive intensive insulin therapy nowadays, and many of them are also treated for several comorbidities. The combination of insulin therapy and other comorbidities could result in an unexpected complication.