Fanconi-Bickel syndrome as an example of marked allelic heterogeneity

Genetic, Clinical, and Biochemical Characterization of a Large Cohort of Palestinian Patients With Fanconi-Bickel Syndrome

This study aims to investigate the clinical, biochemical, and genetic characteristics of Fanconi-Bickel syndrome (FBS) in a cohort of 20 individuals from Palestine and to identify novel pathogenic variants. A retrospective analysis was conducted on medical records from Al-Makassed Hospital's pediatric department spanning 2015 to 2023. Individuals diagnosed with FBS via molecular genetic testing were included in the study. Among the 20 genetically confirmed FBS patients, hepatomegaly was prevalent in 95%, whereas 70% exhibited both developmental delay and hypophosphatemic rickets, and 68.4% experienced growth retardation. Hypertriglyceridemia (HTG) was universal. Elevated liver enzymes and alkaline phosphatase were common, along with hypophosphatemia (95%) and urinary abnormalities. Genetic analysis revealed five distinct SLC2A2 pathogenic variants, including three previously unreported variants: p.Gln23Arg (c.68A > G), p.Thr353Arg (c.1058_1059delinsGG), and an exon 7 deletion. This study presents the largest single-center cohort of FBS patients, expanding our understanding of the disorder's phenotypic and genotypic spectrum. Despite FBS generally carrying a favorable prognosis, timely diagnosis remains crucial to prevent severe complications.

Management of Dysglycemia in a Pregnancy Complicated by Fanconi-Bickel Syndrome

Background/Objective

Fanconi-Bickel Syndrome (FBS) is an inherited disorder of glucose metabolism resulting from functional loss of glucose transporter 2 characterized by fasting hypoglycemia oscillating with postprandial hyperglycemia. Dysglycemia treatment strategies during FBS pregnancy have not been reported, and insulin therapy carries significant risk due to fasting hypoglycemia in FBS. We report for the first time: (1) glycemic profiles obtained via continuous glucose monitoring (CGM), (2) CGM-guided strategies for cornstarch and nutritional therapy for fasting hypoglycemia and postprandial hyperglycemia, respectively, and (3) placental glucose transporter 2 isoform expression in a pregnant individual with FBS.

Case Report

A 27-year-old woman with FBS presented at 6 weeks gestation for management of fasting hypoglycemia and postprandial hyperglycemia. Cornstarch therapy for fasting hypoglycemia and nutritional therapy for postprandial hyperglycemia were iteratively adjusted across gestation based on CGM-derived glycemic patterns. Pregnancy-specific glycemic targets were successfully achieved, and she delivered a healthy term infant. Glucose transporter 2 isoform was not detected in placental tissue.

Discussion

We report for the first time glycemic patterns across gestation in a pregnant individual with FBS. Glycemic targets were achieved through stepwise optimization of nutritional and cornstarch therapy, both guided by CGM data. Our approach obviated the need for insulin therapy, which carries amplified risk in FBS.

Conclusion

Fasting hypoglycemia and postprandial hyperglycemia can be effectively treated through CGM-guided adjustment of both nutritional and glucose polymer therapies in FBS pregnancy. More broadly, our case highlights a novel application for CGM in the management of uncommon glucose metabolism disorders during pregnancy.

Glycogen storage diseases with liver involvement: a literature review of GSD type 0, IV, VI, IX and XI

Background

Glycogen storage diseases (GSDs) with liver involvement are classified into types 0, I, III, IV, VI, IX and XI, depending on the affected enzyme. Hypoglycemia and hepatomegaly are hallmarks of disease, but muscular and renal tubular involvement, dyslipidemia and osteopenia can develop. Considering the paucity of literature available, herein we provide a narrative review of these latter forms of GSDs.

Main body

Diagnosis is based on clinical manifestations and laboratory test results, but molecular analysis is often necessary to distinguish the various forms, whose presentation can be similar. Compared to GSD type I and III, which are characterized by a more severe impact on metabolic and glycemic homeostasis, GSD type 0, VI, IX and XI are usually known to be responsive to the nutritional treatment for achieving a balanced metabolic homeostasis in the pediatric age. However, some patients can exhibit a more severe phenotype and an important progression of the liver and muscular disease. The effects of dietary adjustments in GSD type IV are encouraging, but data are limited.

Conclusions

Early diagnosis allows a good metabolic control, with improvement of quality of life and prognosis, therefore we underline the importance of building a proper knowledge among physicians about these rare conditions. Regular monitoring is necessary to restrain disease progression and complications.

Fanconi-Bickel syndrome in an infant with cytomegalovirus infection: A case report and review of the literature

BACKGROUND

Fanconi-Bickel syndrome (FBS) is a rare autosomal recessive disorder caused by mutation of the SLC2A2 gene, which encodes glucose transporter protein 2 (GLUT2).

CASE SUMMARY

We report a 7-mo-old girl with cytomegalovirus infection presenting hepatomegaly, jaundice, liver transaminase elevation, fasting hypoglycemia, hyperglycosuria, proteinuria, hypophosphatemia, rickets, and growth retardation. After prescription of ganciclovir, the levels of bilirubin and alanine aminotransferase decreased to normal, while she still had aggravating hepatomegaly and severe hyperglycosuria. Then, whole exome sequencing was conducted and revealed a homozygous c.416delC mutation in exon 4 of SLC2A2 inherited from her parents, which was predicted to change alanine 139 to valine (p.A139Vfs*3), indicating a diagnosis of FBS. During the follow-up, the entire laboratory test returned to normal with extra supplement of vitamin D and corn starch. Her weight increased to normal range at 3 years old without hepatomegaly. However, she still had short stature. Although there was heterogeneity between phenotype and genotype, Chinese children had typical clinical manifestations. No hot spot mutation or association between severity and mutations was found, but nonsense and missense mutations were more common. Data of long-term follow-up were rare, leading to insufficient assessment of the prognosis in Chinese children.

CONCLUSION

FBS is a rare genetic metabolic disease causing impaired glucose liver homeostasis and proximal renal tubular dysfunction. Results of urine and blood testing suggesting abnormal glucose metabolism could be the clues for FBS in neonates and infants. Genetic sequencing is indispensable for diagnosis. Since the diversity of disease severity, early identification and long-term follow-up could help improve patients' quality of life and decrease mortality.

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.

Ion Transporters, Channelopathies, and Glucose Disorders

Ion channels and transporters play essential roles in excitable cells including cardiac, skeletal and smooth muscle cells, neurons, and endocrine cells. In pancreatic beta-cells, for example, potassium K_ATP channels link the metabolic signals generated inside the cell to changes in the beta-cell membrane potential, and ultimately regulate insulin secretion. Mutations in the genes encoding some ion transporter and channel proteins lead to disorders of glucose homeostasis (hyperinsulinaemic hypoglycaemia and different forms of diabetes mellitus). Pancreatic K_ATP, Non-K_ATP, and some calcium channelopathies and MCT1 transporter defects can lead to various forms of hyperinsulinaemic hypoglycaemia (HH). Mutations in the genes encoding the pancreatic K_ATP channels can also lead to different types of diabetes (including neonatal diabetes mellitus (NDM) and Maturity Onset Diabetes of the Young, MODY), and defects in the solute carrier family 2 member 2 (SLC2A2) leads to diabetes mellitus as part of the Fanconi–Bickel syndrome. Variants or polymorphisms in some ion channel genes and transporters have been reported in association with type 2 diabetes mellitus.

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.

Fanconi-Bickel Syndrome: Two Pakistani Patients Presenting with Hypophosphatemic Rickets

Fanconi-Bickel syndrome is a rare inherited disorder characterized by hepatorenal glycogen accumulation, renal tubular dysfunction, growth failure, and impaired utilization of glucose and galactose. We report the first two children with Fanconi-Bickel syndrome from Pakistan who presented with classical features of Fanconi-Bickel Syndrome. Both patients were found to be homozygous for a single nucleotide deletion in the SLC2A2 gene defined as c.339delC. This mutation was previously described in an Arab patient who was initially presented as permanent neonatal diabetes mellitus before developing classical features of Fanconi-Bickel syndrome.