ESPE Abstracts

Background: Fanconi Bickel syndrome (FBS) is a rare form of glycogen storage disease (GSD) inherited in an autosomal recessive manner and caused by mutations in the SLC2A2 gene leading to the loss of GLUT2 glucose transporter expression. The disease is considered to be rare in which a little more than 100 cases have been reported in the literature. The SLC2A2 gene encodes for GLUT2, a low affinity facilitative glucose transporter expressed in critical tissues involved in glucose homeostasis such as hepatocytes, pancreatic β-cells,and renal tubular cells. FBS is characterized by impaired utilization of glucose and galactose, tubular nephropathy and hepatorenal glycogen accumulation. Dysfunctional and reduced expression of GLUT2 causes fasting hypoglycemia, postprandial hyperglycemia, diabetes mellitus (DM), hepatomegaly, glucose and galactose intolerance, partial resistance to adrenaline and glucagon, rickets, and poor growth. The role of dysfunctional GLUT2 in the cause of DM is still not clearly understood.

Objective(s): 1. To describe the clinical and genetic characteristics of a new case of FBS patient associated with dysglycemia. 2. To understand the molecular basis of DM in Fanconi Bickel syndrome.

Case report: A 22 months old Palestinian boy, born to first degree cousins, presented with severe proximal tubular dysfunction, hepatomegaly, rickets, developmental delay, and failure to thrive. Biochemical tests showed high levels of random blood glucose but low C-peptide levels. Urine analysis showed proteinuria, glycosuria, phosphaturia and aminoaciduria.

Methodology: Genomic DNA and RNA were isolated from peripheral blood samples, and analyzed by Whole Exome Sequencing (WES) and Sanger sequencing. CRISPR was used to generate the mutation.

Results: A novel homozygous nonsense mutation (c.901C>T) in the SLC2A2 gene (R301X) was found and confirmed by Sanger sequencing. To investigate the impact of this mutation, CRISPR/Cas9 system was used to substitute the nucleotide C by T at position 901. Beta cells were co-transfect by a plasmid carrying Cas9, the specific gRNA to target GLUT2 and DNA oligo donor template to specifically substitute C by T at the position 901. Edited cells carrying the specific mutation were diluted and cultured at low cell concentration to isolate single colonies and establish a Glut2 knock-out cell. The Glut2 knock-out will be used to understand the functional and structural characterization of the disease.

Conclusions: Future directions include doing the functional analysis to clearly understand the molecular mechanisms underlying the disease and develop the targeted precision therapies specifically designed for the molecular changes and associated DM and FBS syndrome.