Kidney Week

Abstract: SA-PO0644

Genetic Roots of Refractory Hypomagnesemia: A Case of Severe Renal Magnesium Wasting

Session Information

• Monogenic Kidney Diseases: Tubular and Other
  November 08, 2025 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1201 Genetic Diseases of the Kidneys: Monogenic Kidney Diseases

Authors

• Vazquez-Fernandez, Paola M., Universidad de Puerto Rico Recinto de Ciencias Medicas, San Juan, Puerto Rico

Paola M. Vazquez-Fernandez, MD

• Burgos Martinez, Lidynell M, Universidad de Puerto Rico Recinto de Ciencias Medicas, San Juan, Puerto Rico

Lidynell M Burgos Martinez, MD

• Gonzalez Rivera, Adriel, Universidad de Puerto Rico Recinto de Ciencias Medicas, San Juan, Puerto Rico

Adriel Gonzalez Rivera, MD

• Ocasio Feliciano, Edilberto Jose, Universidad de Puerto Rico Recinto de Ciencias Medicas, San Juan, Puerto Rico

Edilberto Jose Ocasio Feliciano, MD

• Ocasio Melendez, Ileana E., Universidad de Puerto Rico Recinto de Ciencias Medicas, San Juan, Puerto Rico

Ileana E. Ocasio Melendez, MD, FASN

Introduction

HNF1B mutations are associated with a spectrum of autosomal dominant disorders affecting renal development and tubular function. Among
these, Autosomal Dominant Tubulointerstitial Kidney Disease often presents with subtle electrolyte abnormalities. Hypomagnesemia due to renal magnesium wasting is a hallmark but frequently underrecognized clinical feature.

Case Description

We report a case of a 46-year-old female with a long standing history of refractory hypomagnesemia that came to the clinic with symptoms of fatigue, weakness, muscle spasm and tremors requiring multiple admission for IV magnesium replacement. Medications used include Magnesium 400 mg twice per day. Vital signs showed blood pressure 110/70mmHg, heart rate 70 beat per minute and RR 16. Laboratory results revealed creatinine levels 0.7mg/dL, BUN:35 mg/dL, chloride 105 mmol/L, bicarbonate 24 mmol/L, potassium levels 3.8 meq, Magnesium 1.2 mg/dl, Urine Creatinine 57 mg/dl and Urine Magnesium 37.3 mg/dl. Fractional Excretion of Magnesium (FEMg) calculation revealed a value of 54.53 %, indicative of severe renal magnesium wasting.
Renal ultrasound showed normal-sized kidneys without cysts or structural abnormalities. Given the unexplained hypomagnesemia and early-onset CKD, genetic testing was pursued, which identified a heterozygous pathogenic variant in the HNF1B gene. There was no family history of kidney disease, suggesting a possible de novo mutation. Further evaluation showed mild glycosuria and low- normal serum bicarbonate, consistent with tubulopathy.

Discussion

This case underscores the phenotypic variability of HNF1B-related disorders and emphasizes the importance of genetic testing in patients with unexplained electrolyte disturbances and chronic kidney disease (CKD). HNF1B mutations can lead to progressive tubulointerstitial fibrosis even in the absence of overt structural kidney anomalies such as renal cysts, diabetes syndrome, and Maturity-Onset Diabetes of the Young type 5 .Early recognition may influence family screening and prognosis.
Clinicians should maintain a high index of suspicion for HNF1B-related kidney disease in patients with unexplained hypomagnesemia, even in the absence of a family history or structural abnormalities. Genetic testing is essential for accurate diagnosis and appropriate management.

Digital Object Identifier (DOI)

• doi: 10.1681/ASN.20251rfhrpcw