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Kidney Week

Abstract: FR-PO594

An Un-Hex-Pected Cause of Crystalluria

Session Information

Category: Genetic Diseases of the Kidneys

  • 1202 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Blum, Christina L., Walter Reed National Military Medical Center, Bethesda, Maryland, United States
  • Watson, Maura A., Walter Reed National Military Medical Center, Bethesda, Maryland, United States
  • Joshi, Megha Raj, Walter Reed National Military Medical Center, Bethesda, Maryland, United States
Introduction

Cystinuria, a genetic cause of kidney stones, is present in 1/7000 births, and 75% present in childhood. Cystinuria should be suspected in those with childhood kidney stones, staghorn calculi, or family history of stones. Diagnosis is confirmed by cystine calculi on analysis, hexagonal cystine crystals on microscopic urinalysis, or genetic testing. Patients are at increased risk of developing chronic kidney disease.

Case Description

A 21-year-old man with no significant past medical history presented with acute onset chest pain and dyspnea following a strenuous run. He had a nagging cold and took guaifenesin and half a scoop of workout supplement prior to running. Immediately afterward, he had lightheadedness, paraesthesias, headache, and progressive dyspnea. He had an anion gap of 28, elevated troponin, normal pro-BNP, HCO3 11 meq/L, sCr 1.6 mg/dl (no prior), Ca 10.6 mg/dl, and glucose 277 mg/dl. His symptoms were transient, and although he had acute myocardial injury, cardiac workup was negative. Creatinine peaked at 2.3 mg/dl. Urinalysis was notable for hemoglobinuria and proteinuria; microscopy showed hexagonal crystals. Two 24hr urine collections, 1 month apart, showed elevated cystine and low citrate. He was found to have a heterozygous pathogenic variant in the gene SLC7A9, c.997C>T, p.Arg333Trp consistent with autosomal dominant cystinuria. His father had a stone in his 40s, attributed to diet. While the patient has never had nephrolithiasis, he is at increased risk. He was started on potassium citrate and counseled to increase fluid intake and reduce dietary sodium and animal protein, with a goal urine cystine <250mg/L and urine pH >7.

Discussion

SLC7A9 variants are associated with autosomal dominant and recessive cystinuria, with variable penetrance. Heterozygotes often have increased urine excretion of cysteine and dibasic amino acids, which can lead to nephrolithiasis. Cystinuria was unexpected in this patient, and upon renal recovery urine cystine crystals were absent. The combination of his mild cold, supplement use, and strenuous exercise predisposed him to acute kidney injury and revealed his otherwise quiescent cystinuria. Continued monitoring and treatment is warranted to prevent nephrolithiasis and chronic kidney disease.

The views expressed in this abstract are those of the author(s) and do not necessarily reflect the official policy of the Department of Defense or the U.S. Government.