Fanconi-Bickel syndrome (FBS) [OMIM#227810] is a rare disorder characterized by hepatomegaly secondary to glycogen accumulation, glucose and galactose intolerance, fasting hypoglycemia, tubular nephropathy, rickets and growth retardation. Elevated glucose levels have been detected in some patients under 1 year of age and FBS should thus be considered in the differential diagnosis of neonatal diabetes when any of the other characteristic features are also present.
SLC2A2 [OMIM#138160] encodes for the facilitative glucose transporter GLUT2. Mutations in SLC2A2 associated with FBS lead to severely impaired glucose transport. Sakamoto et al (2000) noted glucosuria in some heterozygous carriers for SLC2A2 missense mutations; carriers of nonsense mutations did not appear to have the same finding. It has been speculated that the glucosuria seen in missense mutation carriers is due to a dominant negative effect, which may not occur with nonsense mutations due to nonsense-mediated decay.