Fanconi-Bickel syndrome (FBS) is a rare, autosomal recessive disorder of carbohydrate metabolism caused by defects in the facilitative glucose transporter 2 (GLUT2 or SLC2A2) gene. Prominent findings are failure to thrive, renal tubular acidosis, hypoglycemia and postprandial hyperglycemia even mimicking diabetes mellitus. Eight patients from 6 families with FBS were included in this study. c.482_483insC homozygous mutation was detected in six patients from four different families. Mutation analysis of SLC2A2 gene revealed two novel homozygous mutations; c.1069delGinsAATAA and c.575A > G. Standard oral glucose tolerance test with 1.75 g/kg oral glucose was performed in six of the patients who were older than 3-years of age. Impaired glucose tolerance was found in all patients as expected and two of them had overt diabetes. None of the antidiabetic medications were given to them in order to avoid significant hypoglycemia. Beside the conservative treatment, follow up with frequent oral glucose tolerance tests are planned. We report these cases of FBS, as GSD XI is rare, two novel mutations were detected and also to highlight the risk of diabetes mellitus; although there is not a consensus about the treatment.

Keywords: Fanconi-Bickel syndrome, hypoglycemia, oral glucose tolerance test, postprandial hyperglycemia