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Abstract: FR-PO611

Hypokalemia in an Older Adult due to Heterozygosity for a Novel Pathogenic Variant that Causes Gitelman Syndrome

Session Information

Category: Genetic Diseases of the Kidneys

  • 1202 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Alzyood, Laith, Albert Einstein College of Medicine, Bronx, New York, United States
  • Fisher, Molly, Albert Einstein College of Medicine, Bronx, New York, United States
Introduction

Gitelman Syndrome (GS) is a rare autosomal recessive disorder due to a mutation in the SLC12A3 gene that encodes thiazide-sensitive sodium-chloride cotransporter (NCCT) in the distal convoluted tubule. GS classically presents as a salt-losing tubulopathy characterized by low-normal blood pressure, hypokalemia, hypomagnesemia, and metabolic alkalosis and is typically diagnosed in childhood or adolescence. We present an unexpected case of isolated hypokalemia in an older adult with HIV due to a heterozygous SLC12A3 variant mutation.

Case Description

A 63-year-old male with well controlled hypertension, coronary artery disease and HIV with undetectable viral load was referred for hypokalemia. He had intermittent hypokalemia for at least 15 years with potassium as low as 2.7 mEq/L. He had no symptoms of gastrointestinal loss of potassium or family history of hypokalemia. Medications included losartan 50 mg daily, metoprolol 50 mg daily, and amlodipine 10 mg daily, potassium chloride 10 mEq thrice daily, emtricitabine-tenofovir alafenamide 200-25 mg daily, and dolutegravir 50 mg daily. His blood pressure was 110/75 mmHg. Serum magnesium and phosphate were normal and serum bicarbonate ranged from 25-28 mEq/L. Urine spot potassium was 43 mEq/L and fractional excretion of potassium was 11%, indicating renal potassium wasting. Screening for hyperaldosteronism was negative. A prior computed tomography showed a hyperdense appearance to the renal medullary pyramids and several non-obstructing kidney stones. Due to concern for an underlying genetic etiology of his hypokalemia, genetic testing was performed which revealed a heterozygous single amino acid substitution of Glu to Asp at codon 121 in exon 2 of the SLC12A3 gene.

Discussion

Our patient was heterozygous for a pathogenic variant in the SLC12A3 gene that causes GS. Though the inheritance pattern of GS is autosomal recessive, we believe our patient’s isolated renal potassium wasting reflects an intermediate disease phenotype that may be seen in heterozygous carriers. A prior study found heterozygosity for the p.R642G variant was associated with lower serum potassium but to our knowledge, this is the first report of hypokalemia associated with the c.363G variant. This case supports the concept that pathogenic variants, known to cause many recessive disorders, contribute to complex traits.