A Case of Gitelman Syndrome and Poorly Controlled Type 2 Diabetes

Abstract

A 53-year-old woman who consumed a substantial amount of sweet soft drinks visited a diabetologist due to thirst and polydipsia. Her blood glucose was 498 mg/dL, and HbA1c was 13.0 %. Insulin therapy was immediately started. Although the fasting serum C peptide level was 0.64 ng/dL, she had been obese, and anti-GAD antibody was negative. Therefore, type 2 diabetes mellitus was diagnosed, and insulin was substituted for oral therapy with metformin and sitagliptin. Although her glycemic control was excellent, her serum potassium level was 2.9 mmol/L with a serum magnesium level of 1.8 mg/dL, urinary potassium 27.0 mmol/g creatinine, urinary calcium 0.01 g/g creatinine, HCO₃^- 30.7 mmol/L on an arterial blood gas analysis, plasma renin activity 6.5 ng/mL/h, and normal blood pressure and renal ultrasound findings. These clinical findings strongly suggested a diagnosis of Gitelman syndrome. Subsequently, we performed genetic testing for comprehensive genetic tubular diseases using a next-generation sequencing-based gene panel. As a result, triple mutations (A569V, L585H, G898W) were identified, which were previously reported as pathogenic missense mutations. Administration of KCL and MgO₂ kept the serum potassium and magnesium levels above 3.5 mmol/L and 1.8 mg/dL, respectively. The effect of coexisting Gitelman syndrome on treatment of diabetes and the development of diabetic complications remains to be elucidated.