Fanconi-Bickel syndrome in two Palestinian children: marked phenotypic variability with identical mutation

The SGLT2 inhibitor dapagliflozin improves kidney function in glycogen storage disease XI

Glycogen storage disease XI, also known as Fanconi-Bickel syndrome (FBS), is a rare autosomal recessive disorder caused by mutations in the SLC2A2 gene that encodes the glucose-facilitated transporter type 2 (GLUT2). Patients develop a life-threatening renal proximal tubule dysfunction for which no treatment is available apart from electrolyte replacement. To investigate the renal pathogenesis of FBS, SLC2A2 expression was ablated in mouse kidney and HK-2 proximal tubule cells. GLUT2Pax8Cre+ mice developed time-dependent glycogen accumulation in proximal tubule cells and recapitulated the renal Fanconi phenotype seen in patients. In vitro suppression of GLUT2 impaired lysosomal autophagy as shown by transcriptomic and biochemical analysis. However, this effect was reversed by exposure to a low glucose concentration, suggesting that GLUT2 facilitates the homeostasis of key cellular pathways in proximal tubule cells by preventing glucose toxicity. To investigate whether targeting proximal tubule glucose influx can limit glycogen accumulation and correct symptoms in vivo, we treated mice with the selective SGLT2 inhibitor dapagliflozin. Dapagliflozin reduced glycogen accumulation and improved metabolic acidosis and phosphaturia in the animals by normalizing the expression of Napi2a and NHE3 transporters. In addition, in a patient with FBS, dapagliflozin was safe, improved serum potassium and phosphate concentrations, and reduced glycogen content in urinary shed cells. Overall, this study provides proof of concept for dapagliflozin as a potentially suitable therapy for FBS.

Acquired growth hormone deficiency in Fanconi-Bickel syndrome

Fanconi-Bickel syndrome (FBS) is a rare autosomal recessive disease, resulting from mutations in the SLC2A2 gene, causing impaired glucose transporter 2 protein transporter protein function, impaired glucose and galactose utilisation, hepatorenal glycogen accumulation and organ dysfunction. Clinical features include failure to thrive, hepatomegaly, rickets, short stature and delayed puberty. Therapy includes electrolyte supplementation and uncooked cornstarch. We present a 15-year-old boy diagnosed with FBS in infancy. Growth velocity was normal on standard treatment until age 8.5 years, at which time growth failure led to a diagnosis of acquired growth hormone (GH) deficiency. Initiation of recombinant human GH (rhGH) replacement of 0.25 μg/kg/week resulted in marked improvement in growth velocity and height. While short stature is expected in FBS, growth velocity that falls below the normal range despite adequate therapy should prompt further evaluation. Our case suggests that acquired GH deficiency can arise in FBS and benefits from rhGH therapy.

Fanconi–Bickel syndrome in a Ugandan child – diagnostic challenges in resource-limited settings: a case report

Background

Fanconi–Bickel syndrome is an autosomal recessive disorder of glucose metabolism. It is an extremely rare disorder. Most cases have been reported in consanguineous communities. None of the cases have been reported in Black Africans in sub-Saharan Africa. This case was diagnosed 3 years after initial presentation due to diagnostic challenges and limited awareness of similar metabolic syndromes in our setting.

Case presentation

We report the case of a 4-year-old boy, born to non-consanguineous Black African parents, who presented with failure to thrive and rachitic features in infancy. Clinical, laboratory, and radiological features were indicative of Fanconi–Bickel syndrome. No genetic testing was done. The diagnosis was made 3 years after the initial presentation due to diagnostic challenges. He showed clinical improvement with the institution of a galactose-free diet.

Conclusion

Fanconi–Bickel syndrome occurs even in non-consanguineous Black African populations. Therefore, clinicians in resource-poor settings should raise their index of suspicion for such metabolic disorders in settings with a high prevalence of failure to thrive among children.

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.

Nocturnal enteral nutrition is therapeutic for growth failure in Fanconi-Bickel syndrome

Fanconi-Bickel syndrome (FBS) is a rare autosomal recessive disorder characterised by impaired glucose liver homeostasis and proximal renal tubular dysfunction. It is caused by pathogenic variants in SLC2A2 coding for the glucose transporter GLUT2. Main clinical features include hepatomegaly, fasting hypoglycaemia, postprandial hyperglycaemia, Fanconi-type tubulopathy occasionally with rickets, and a severe growth disorder. While treatment for renal tubular dysfunction is well established, data regarding optimal nutritional therapy are scarce. Similarly, detailed clinical evaluation of treated FBS patients is lacking. These unmet needs were an incentive to conduct the present pilot study. We present clinical findings, laboratory parameters and molecular genetic data on 11 FBS patients with emphasis on clinical outcome under various nutritional interventions. At diagnosis, the patients' phenotypic severity could be classified into two categories: a first group with severe growth failure and rickets, and a second group with milder signs and symptoms. Three patients were diagnosed early and treated because of family history. All patients exhibited massive glucosuria at diagnosis and some in both groups had fasting hypoglycaemic episodes. Growth retardation improved drastically in all five patients treated by intensive nutritional intervention (nocturnal enteral nutrition) and uncooked cornstarch with final growth parameters in the normal range. The four severely affected patients who were treated with uncooked cornstarch alone did not catch up growth. All patients received electrolytes and l-carnitine supplementation to compensate for the tubulopathy. This is one of the largest series of FBS on therapeutic management with evidence that nocturnal enteral nutrition rescues growth failure.

Glycosuria and hyperglycemia in the neonatal period as the first clinical sign of Fanconi-Bickel syndrome

Fanconi-Bickel syndrome is a rare inherited disease characterized by the combination of hepatorenal glycogen accumulation, proximal renal tubular dysfunction and impaired utilization of glucose and galactose. The first symptoms of the disorder are recognized in late infancy as clinical characteristics appear. Therapeutic approach is mainly conservative with supplements of calcium, phosphate and vitamin D and small frequent feedings to avoid hypoglycemia. We report 1 clinical case of very early diagnosis, a 19 days old baby girl, in which the first clinical sign of the disease was the detection of glycosuria and vomits. Serum alkaline phosphatase levels were very high without rickets. The patient presented postprandial hyperglycemia and fasting hypoglycemia. A complete 24-hour glucose profile was obtained using a continuous glucose monitoring system in real time, which was fundamental not only for the diagnosis but also for the prevention of hypoglycemia. She received frequent small meals, galactose-free milk diet, and oral intakes of calcium, phosphorum, bicarbonate and vitamin D supplements with good evolution and normal height and weight gain.

Fanconi syndrome and neonatal diabetes: phenotypic heterogeneity in patients with GLUT2 defects

Fanconi-Bickel syndrome, caused by mutations in SLC2A2 encoding the glucose transporter 2 (GLUT2), is characterized by generalized proximal renal tubular dysfunction manifesting in late infancy. We describe phenotypic heterogeneity of Fanconi-Bickel syndrome in three siblings, including early and atypical presentation with transient neonatal diabetes mellitus in one. The second-born of a non-consanguineous couple, evaluated for polyuria and growth retardation, had rickets, hepatomegaly and proximal tubular dysfunction from 4 to 6  months of age. A male sibling, who expired at 4 months, also had hepatomegaly and growth retardation. The third sibling had polyuria, glucosuria and mild proteinuria on day 3 of life. Hyperglycemia was detected 2 weeks later, which required therapy with insulin for 3 months. Mild metabolic acidosis was present at 2 weeks; hypercalciuria, phosphaturia and aminoaciduria were seen at 6 months. Sanger sequencing showed a homozygous missense mutation in SLC2A2 (exon 7, c.952G > A), causing glycine to arginine substitution; both parents were heterozygous carriers. Patients with SLC2A2 mutations may present either with isolated neonatal diabetes or with hepatomegaly and the renal Fanconi syndrome. Fanconi-Bickel syndrome shows phenotypic heterogeneity and may manifest early with subtle or atypical features, mandating a high index of suspicion.