Sweet Without the Sour: A Genetic Tale of Sugar Loss

Introduction: The vast majority of glycosuria is caused by hyperglycemia in diabetes mellitus, but in patients who do not have this, it should prompt further investigation. We present a case of glycosuria in the absence of hyperglycemia. Case Description: A 35-year-old female, G2P2, with a medical history of migraines with aura, and recurrent urinary tract infections (UTIs) presented to nephrology due to persistent glycosuria. She was taking indomethacin, tizanidine and rimegepant. She was not on a sodium-glucose cotransporter 2 (SGLT-2) inhibitor or a carbonic anhydrase inhibitor. No significant family history. Review of patient's labs from the past 10 years showed that all her urine samples had been positive for glucose with normal kidney function. Her potassium levels have varied between 3.1 to 4.1 mEq/L. Her urine was positive for ketones at 35 weeks gestation during both her pregnancies. Workup was negative for serum protein electrophoresis, serum immunofixation, and heavy metal screen. Urine microscopic exam was unremarkable except for glycosuria. Genetic testing was eventually perused which showed a heterozygous mutation in the SLC5A2 gene. Discussion: Normally, glucose is reabsorbed in the kidney via SGLT-2 and GLUT2, but excessive serum glucose saturates this process. In rare cases, euglycemic patients may still have glycosuria, suggesting impaired tubular reabsorption due to Fanconi syndrome. Another possible etiology is an autosomal dominant mutation in SLC5A2, the gene encoding for SGLT-2, which manifests as familial renal glycosuria. This condition is characterized by urinary glucose wasting due to decreased tubular resorption of glucose in the absence of hyperglycemia and any other signs of tubular dysfunction. Biallelic pathogenic variants are associated with more severe renal glucose wasting than heterozygous variants. The clinical presentation of individuals with a heterozygous SLC5A2 variant is highly variable and can range from asymptomatic, to childhood onset polyuria, enuresis, mild growth delays, recurrent UTIs, or delayed puberty. Severe cases may present with episodic dehydration and ketosis during pregnancy or starvation. These risks can be mitigated through education on genitourinary hygiene and frequent monitoring during pregnancy. This highlights the importance of genetic testing, since proper diagnosis can affect future management decisions.