Fanconi–Bickel Syndrome: A Review of the Mechanisms That Lead to Dysglycaemia

Accumulation of glycogen in the kidney and liver is the main feature of Fanconi–Bickel Syndrome (FBS), a rare disorder of carbohydrate metabolism inherited in an autosomal recessive manner due to SLC2A2 gene mutations. Missense, nonsense, frame-shift (fs), in-frame indels, splice site, and compound heterozygous variants have all been identified in SLC2A2 gene of FBS cases. Approximately 144 FBS cases with 70 different SLC2A2 gene variants have been reported so far. SLC2A2 encodes for glucose transporter 2 (GLUT2) a low affinity facilitative transporter of glucose mainly expressed in tissues playing important roles in glucose homeostasis, such as renal tubular cells, enterocytes, pancreatic β-cells, hepatocytes and discrete regions of the brain. Dysfunctional mutations and decreased GLUT2 expression leads to dysglycaemia (fasting hypoglycemia, postprandial hyperglycemia, glucose intolerance, and rarely diabetes mellitus), hepatomegaly, galactose intolerance, rickets, and poor growth. The molecular mechanisms of dysglycaemia in FBS are still not clearly understood. In this review, we discuss the physiological roles of GLUT2 and the pathophysiology of mutants, highlight all of the previously reported SLC2A2 mutations associated with dysglycaemia, and review the potential molecular mechanisms leading to dysglycaemia and diabetes mellitus in FBS patients.

Hepatocellular Carcinoma in Fanconi-Bickel Syndrome

Fanconi-Bickel syndrome is a rare autosomal recessive disorder due to mutations in the facilitative glucose transporter 2 ( GLUT2 or SLC2A2) gene resulting in excessive glycogen storage predominantly in the liver and kidney. Previous case reports of this condition have described liver biopsies with glycogen storage and variable steatosis and/or fibrosis. Unlike in other types of glycogen storage disease, hepatocellular adenomas and carcinomas have not been described to date in this syndrome. A 6-year-old boy with consanguineous parents had short stature, poorly controlled rickets, hepatosplenomegaly, and renal tubular dysfunction clinically consistent with Fanconi-Bickel Syndrome. Sequencing of the SLC2A2 gene showed a homozygous variant of unknown significance [c.474A > C (p.Arg158Ser)] causing a missense mutation in an evolutionarily conserved residue. An incidental single hepatic lesion was discovered on imaging, and subsequent resection showed a 2.6 cm well-differentiated hepatocellular carcinoma with moderate atypia, diffuse immunoreactivity for glypican-3, and nuclear b-catenin, and with focal complete loss of the reticulin framework. The non-neoplastic liver showed marked glycogen accumulation with mild periportal fibrosis, rare bridging fibrosis, and no regenerative or adenomatous nodules. By electron microscopy, tumor cells had pleomorphic nuclei, prominent nucleoli, and scant cytoplasm with numerous mitochondria. Well-developed canaliculi were occasionally seen. The non-neoplastic liver showed glycogenosis with abundant cytoplasmic free (non-membrane bound) glycogen. Hepatocellular carcinoma should be considered as a possible complication of Fanconi-Bickel syndrome. This well differentiated carcinoma did not appear to be associated with hepatic adenomatosis as has been described in some hepatocellular carcinomas associated with other hepatic glycogen storage disorders. The nuclear beta-catenin immunoreactivity indicates a role for the Wnt signaling pathway in the pathogenesis of this tumor.

Genetic markers of type 2 diabetes in Russian population

Introduction. Genetic susceptibility to Type 2 Diabetes (T2D) with a complex mode of inheritance is explained by the presence of multiple gene, each conferring a small moderate contribution the overall risk, as well as by alternative combinations of genes. Due to the success of Genome-Wide Association Study there has been rapid increase in the availability of genetic data for T2D. This allows the collection of large sets of genetic polymorphic loci, which could be key in the understanding of the genetic basis of T2D.The aim of this study was to determine alleles and allelic combinations that are associated with T2D phenotype.Methods. We assessed the associations of 96 single nucleotide polymorphisms (SNPs) linked with T2D different pathway components and carbohydrate metabolism abnormalities in 96 Russian patients and 96 normoglycemic controls using Illumina Golden Gate Genotyping Assay (low density DNA chip with 96 SNPs). T2D was defined according to the World Health Organization criteria, 1999. Data were analyzed with the free online statistical program named “Calculator for confidence intervals of odds ratio” (www.gen-exp.ru/calculator_or.php) and APSampler software (https://code.google.com/p/apsampler) for multi-locus association analysis.Results. On the first stage of the study we detected ten SNPs that can be independently contributing to T2D risk in the Russian cohort, they are rs8050136 (p=0,05) and rs11642841 (p=0,04) in FTO gene, rs2943641 (p=0,02) and rs2943634 (p=0,03) in IRS1 gene, rs571312 in MC4R gene, rs1470579 (p=0,04) in IGF2BP2 gene, rs163184(p=0,03) in KCNQ1 gene, rs11924032 (p=0,04) in SLC2A2 gene, rs11634397 (p=0,03) in ZFAND6 gene, rs7172432(p=0,04) in C2CD4A gene. On the second stage we found a biallelic combination of A allele rs8050136 in FTO gene and A allele rs7172432 in C2CD4R gene that was associated with T2D risk. Remarkable, the combined effect (association) of rs8050136 and rs7172432 was stronger (OR=1,97; p=0.006) than that of each SNP alone.Conclusion. The biallelic combination of A allele rs8050136 in FTO gene and A allele rs7172432 in C2CD4R gene can be used as a genetic marker of T2D.