Mutation in the SLC2A9 Gene: A New Family with Familial Renal Hypouricemia Type 2

Familial renal hypouricemia is a rare genetic disorder characterized by a defect in renal tubular urate reabsorption. Some patients present with exercise-induced acute kidney injury and nephrolithiasis. Type II is caused by mutations in the SLC2A9 gene. Here, we report the case of a young patient who developed acute kidney injury after exercise secondary to familial renal hypouricemia type II. The same mutation was found in other asymptomatic members of his family. We review the medical literature on this condition. This case highlights the importance of considering uric acid disorders in the work-up of acute kidney injury after exercise.


Case Presentation
A 20-year-old man presented to the nephrology department with acute pain of both flanks which started after a physical exercise at school. His past medical history was unremarkable. He was not taking any medications or illicit drugs, and he denied smoking and consuming alcohol.
ere was no abnormal finding in his physical examination. Vital signs were normal. Laboratory tests on admission showed acute kidney injury with a creatine kinase level of only twice the upper limit of the normal (Table 1). Urinalysis was bland, and the proteinuria was within the range (Table 1). Contrast-enhanced computed tomography showed decreased enhancement of the kidneys without any abnormality of the vessels and showed no urolithiasis. After conservative therapy including intravenous fluid administration, the renal function recovered gradually and returned to the normal at the fourth day after admission. e patient reported that he was admitted 4 months ago in the emergency room of another hospital for a similar pain which occurred also after a strenuous exercise. Although laboratory tests showed acute kidney injury, he was discharged without any further investigation.
Laboratory tests were marked by severe hypouricemia. e elevated fractional excretion of urate (119%; N < 10%) suggested a highly increased urinary excretion of uric acid with tubular secretion. Blood and urinary tests showed no argument for Fanconi syndrome or syndrome of inappropriate antidiuretic hormone. Interesting enough, severe hypouricemia was also found in the laboratory tests of his mother and one of his maternal aunts. e occurrence of two episodes of acute kidney injury following intense exercise with the presence of hereditary severe hypouricemia highly suggested exercise-induced acute kidney injury due to familial renal hypouricemia.
is index patient (V6) is a member of a highly consanguineous Pakistani family with cousin marriages over two successive generations (Figure 1    Case Reports in Nephrology technique [5]. Genetic testing of the patient's mother revealed the same homozygous mutation. Severe hypouricemia with the familial homozygous mutation was found in two of his clinically unaffected sisters (V7 and V9). e third sister (V8) is heterozygous for the mutation and is presenting with normal uric acid level. Profound hypouricemia was also measured in one of his aunts (IV2) and one of his cousins (V12). All of these analyses confirmed an autosomal recessive mode of inheritance. Besides the index patient, no medical history was known in all of the family members except his grandfather (III5) who suffered from kidney stones.
Data Availability e datasets used during the current study are available from the corresponding author on reasonable request.

Consent
Informed consent was obtained from the patient.

Conflicts of Interest
e authors declare no conflicts of interest.