Fanconi-Bickel syndrome is associated with a defect in which transporter?

• A. Glucose transporter 2 (GLUT2)
• B. GLUT4
• C. SGLT1
• D. GLUT1

Answer: (A)

GLUT2 is the basolateral glucose transporter in liver and kidney, allowing glucose to exit cells into the bloodstream. Fanconi-Bickel syndrome arises from mutations in SLC2A2, the gene encoding GLUT2, leading to defective glucose export from hepatocytes and from proximal renal tubule cells. This explains why patients develop hepatomegaly from glycogen accumulation in the liver and a proximal-tubule–like—Fanconi—gu," with glucosuria, aminoaciduria, and phosphate wasting due to impaired reabsorption. The other transporters have different roles: GLUT4 is insulin-responsive in muscle and fat; GLUT1 provides basal glucose to many tissues; SGLT1 is a sodium-glucose cotransporter in the intestine and kidney. Thus, a defect in GLUT2 best accounts for Fanconi-Bickel syndrome.