Identification of a novel form of renal glucosuria with overexcretion of arginine, carnosine, and taurine.

Glucosuria occurs in diabetes mellitus, generalized proximal tubular dysfunction of Fanconi's syndrome, glucose-galactose malabsorption syndrome, and primary renal glucosuria. Patients with primary renal glucosuria have normal blood glucose levels, normal oral glucose tolerance test results, and persistent glucosuria that may approach the filtered load of glucose in the most severe cases. The primary defect is proposed to be in the sodium-glucose cotransporter type-2 (SGLT2) located in the apical membrane of S1 segment proximal renal tubule cells. Primary renal glucosuria is classified as types A, B, or O based on the characteristics of the transport defect. The magnitude of glucosuria has varied from 20 to 150 g of glucose excreted in 24 hours. Described inheritance patterns have included both autosomal dominant and autosomal recessive mechanisms. Some cases have been associated with selective aminoaciduria, distinctly unlike the generalized aminoaciduria seen in Fanconi's syndrome. We report the first case of primary renal glucosuria with selective overexcretion of arginine, carnosine, and taurine. This case may represent a genetic defect unique from the abnormalities in previously described cases of primary renal glucosuria with different amino acid excretion patterns. Future investigations could determine whether the syndrome involves a defect in the SGLT2 gene.

Complete absence of tubular glucose reabsorption: a new type of renal glucosuria (type 0).

Primary renal glucosuria is an inherited defect of tubular glucose reabsorption and usually classified in type A and type B. We now observed a new type in a 15-year-old boy who had a complete absence of tubular glucose reabsorption. His father had a daily glucosuria of 1.1 g/1.73 m2 and his mother of 2.7 g/1.73 m2. Two siblings excreted 0.4 g/1.73 m2 and 0.3 g/1.73 m2 glucose and one sister had no glucosuria. The proband excreted daily 136 to 160 g/1.73 m2 glucose accompanied by normal blood glucose levels between 75-105 mg/dl. The glomerular filtration rate (inulin clearance) was 148-153 ml/min/1.73 m2 and the endogenous glucose clearance was 112-160 ml/min/1.73 m2 when blood glucose levels were 72-82 mg/dl. Thus, glucose clearance was nearly identical to inulin-clearance. After intravenous glucose loading with a blood glucose concentration of 261-342 mg/dl, glucose clearance remained in the same range and tubular glucose reabsorption was virtually absent. There were no disturbances in tubular reabsorption of other substrates. This new type of primary renal glucosuria was not recognized thus far, and we propose to call it type O glucosuria. The family tree revealed consanguinity and most probably the proband is homozygous and both his parents are heterozygous for type O renal glucosuria.