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Kidney Week

Abstract: SA-PO700

Years of Hypomagnesemia due to an HNF1B Mutation

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

  • Kim, Isaac Inhwak, University of Cincinnati, Cincinnati, Ohio, United States
  • Gudsoorkar, Prakash Shashikant, University of Cincinnati, Cincinnati, Ohio, United States
Introduction

Mutations in the hepatocyte nuclear factor 1B (HNF1B) are an inherited cause of renal malformation that is accompanied by magnesium wasting and a distal tubular dysfunction like Gitelman syndrome. We describe a patient in late adulthood who has hypomagnesemia and an HNF1B mutation.

Case Description

A 39-year-old female presented with intractable nausea and loose stools. She denied any family history of kidney disease. Her laboratory findings revealed a magnesium of 1.0 mg/dL and a potassium of 3.3 mg/dL. Her FeCa was < 0.1% and FeMg was 5.6%. She reported multiple visits to her PCP for IV magnesium infusions twice per week in addition to oral supplementation. She otherwise denied any symptoms of paresthesia or numbness. Genetic testing was performed and revealed a deficiency in HFNB1.

She was started on amiloride in an effort to decrease magnesium supplementation. Her subsequent visit revealed a magnesium of 1.4 mg/dL. Renal ultrasound also revealed an innumerable amount of bilateral renal cysts, one of which measured 2.5 cm on the upper pole of the right kidney. No solid renal mass was identified.

Discussion


HNF1B is a transcription factor that is highly expressed in multiple organs that include the kidney, pancreas, and liver. It plays a role in morphological renal development in the form of cystic kidney disease, but also can increase the risk of renal tubular dysfunction and progressive CKD. An HNF1B-related hypomagnesemia may be associated with alteration of the Na/K ATPase in the distal convoluted tubule (DCT). Hypocalciuria occurs when sodium reabsorption in the DCT is impaired, as in Gitelman syndrome and in mutation of the FXYD2 gene. Our patient likely had longstanding subclinical HNF1B-related hypomagnesemia but was exaggerated in late adulthood by gastrointestinal losses. She has been asymptomatic but still requires frequent magnesium infusions despite amiloride use.

Pertinent lab findings of the patient
ParameterInitial PresentationFollow-up 5 months laterNormal Range
Creatinine (mg/dL)0.680.880.6-1.3
Magnesium (mg/dL)1.01.41.5-2.5
Calcium (mg/dL)9.59.98.6-10.3
Phosphorus (mg/dL)3.43.92.1-4.7
Albumin (g/dL)Not obtained4.63.5-5.7
FeCa (%)< 0.1< 0.1> 1
FeMg (%)5.6Not obtained< 4
PTH (pg/mL)29.550.012.0-88.0