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Abstract: FR-PO604

Severe Hypomagnesemia as the Initial Indicator of HNF1β-Associated Renal Disease

Session Information

  • Trainee Case Reports - III
    October 26, 2018 | Location: Exhibit Hall, San Diego Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Trainee Case Reports

  • 1600 Pediatric Nephrology

Authors

  • Mann, Nina, Boston Children's Hospital, Boston, Massachusetts, United States
  • Ferguson, Michael A., Boston Children's Hospital, Boston, Massachusetts, United States
  • Stein, Deborah R., Children's Hospital Boston, Boston, Massachusetts, United States
Introduction

Mutations in HNF1β (hepatocyte nuclear factor-1-beta) are known to cause Renal Cysts and Diabetes Syndrome (RCAD), so-named for two common clinical manifestations, maturity-onset diabetes of the young (MODY) and renal cystic disease. However, it has become increasingly recognized that HNF1β-associated disease can lead to a wide spectrum of clinical manifestations affecting multiple organ systems, with varying degrees of renal involvement. Due to the clinical heterogeneity, a high index of suspicion is required in making the diagnosis. Here, we present a case in which severe hypomagnesemia led to a diagnosis of RCAD.

Case Description

A 13-year-old Caucasian girl with newly diagnosed insulin-dependent diabetes mellitus presented with one month of intermittent lower abdominal pain, dysuria, and urinary frequency, and one day of paresthesias. On initial assessment, she appeared tired, but otherwise had an unremarkable physical examination. Laboratory studies revealed severe hypomagnesemia (0.6 mg/dL (normal range 1.5 to 2.2 mg/dL)) and hypocalcemia (ionized calcium of 0.75 mmol/L (normal 1.14 to 1.29 mmol/L)), as well as mild acute kidney injury (Creatinine 1.0 mg/dL) and metabolic alkalosis (bicarbonate 31 mmol/L and venous pH 7.5). Urinalysis revealed 3+ protein and 2+ glucose. Fractional excretion of magnesium was inappropriately elevated at 11%, and urinary calcium was undetectable. A renal ultrasound demonstrated a single 1.3 cm simple cyst in the right kidney. The patient received IV calcium and magnesium supplementation, and was ultimately transitioned to enteral magnesium oxide supplements. Subsequent genetic testing revealed a large deletion of chromosome 17q12. Upon retrospective chart review, it was found that at the time of her initial presentation with diabetes mellitus one month prior, the patient had mild hypomagnesemia and, unusually, a metabolic alkalosis.

Discussion

Mutations in HNF1β can lead to impaired magnesium handling in the distal convoluted tubule, but hypomagnesemia remains an under-recognized manifestation of HNF1β-associated disease. This case highlights that hypomagnesemia should be an indicator to test for mutations in HNF1β, particularly if present in conjunction with early-onset diabetes or urinary tract malformations.