Multidisciplinary Management and Individualized Care in Pregnancy with

Introduction

Fanconi–Bickel syndrome (FBS), also known as glycogen storage disease type XI (GSD XI), is an autosomal recessive inherited disorder, that was initially described in 1949.¹ It is caused by many different mutations in the gene SLC2A2, which encodes glucose transporter membrane protein-2 (GLUT2) and is predominantly expressed in different tissues such as hepatocytes, pancreatic beta cells, intestinal epithelial cells and renal proximal tubular cells.² It is characterized by its low-affinity but high-capacity glucose transport properties, which enable rapid bidirectional movement of glucose and galactose across cell membranes in response to concentration gradients.³

GLUT2 plays a central role in glucose and galactose homeostasis across multiple organs. In the liver, it enables bidirectional glucose flux, supporting glycogen storage postprandially and glucose release during fasting. Loss of this function leads to hepatic glycogen accumulation, hepatomegaly, and dysregulated blood glucose levels.^4,5 In pancreatic β-cells, GLUT2 acts as a key glucose sensor for insulin secretion, and its dysfunction impairs normal insulin regulation.⁶ In the renal proximal tubules, GLUT2 mediates glucose reabsorption. Defective transport results in glucosuria and generalized proximal tubular dysfunction consistent with FBS.⁷ In the intestine, GLUT2 facilitates dietary glucose and galactose absorption into the portal circulation. Impaired function may contribute to carbohydrate malabsorption and metabolic dysregulations.⁸

FBS is a rare metabolic condition characterized by a broad phenotypic spectrum with significant variability in presentation, development of symptoms and severity, and overlaps with more common conditions, making the clinical diagnosis challenging.⁹ The main common clinical features at presentation include general failure to thrive, hepatomegaly secondary to hepatorenal glycogen accumulation and impairment of glucose and galactose tolerance, fasting hypoglycemia and postprandial hyperglycemia, significant glycosuria, proximal tubular nephropathy and later life findings such as osteoporosis and nutritional rickets.^9–11

This study describes the rare case of a 29-year-old pregnant woman affected by a mild form of FBS and details the laboratory and complex therapeutic management throughout her high-risk pregnancy. The identification of a pathogenic SLC2A2 mutation in the patient confirms the molecular basis of FBS and provides a unifying explanation for the constellation of clinical findings, including renal tubular dysfunction leading to proximal renal tubular acidosis and glycosuria, and impaired glucose handling. Understanding the specific impact of the SLC2A2 mutation elucidates the pathophysiological mechanism underlying the patient’s metabolic derangements and supports the rationale for targeted dietary and supportive management.

Case Presentation

Our patient, a member of a highly consanguineous Druze family in central Galilee (Israel), was referred at age 5 for further evaluation of renal glycosuria, hypercalciuria and generalized aminoaciduria and was diagnosed with autosomal recessive proximal tubulopathy and hypercalciuria (ARPTH), a syndrome previously not described in the literature.¹² Subsequent genome-wide homozygosity mapping revealed a novel homozygous missense mutation c.372A>C in GLUT2, resulting in the substitution of an evolutionarily conserved arginine in the first intracellular loop with a serine (R124S).¹³ This mutation occurs in the gene associated with FBS, which can manifest with a wide array of clinical and biochemical presentations, potentially due to the compromised expression of renal sodium-phosphate cotransporter 2c (Npt2c) within the proximal tubules.¹³

At age 24, she presented to our hepatology clinic due to prolonged elevation of liver enzymes. She was unaware of her genetic condition, largely because of the transition from handwritten archived medical records to electronic records over time, as well as strict medical confidentiality policies regarding the reporting of genetic diseases. A preliminary investigation was conducted, encompassing comprehensive laboratory blood tests, abdominal ultrasound, abdominal CT-scans and magnetic resonance imaging (MRI), revealing concurrent renal and hepatic abnormalities, including manifestations of proximal tubulopathy, generalized aminoaciduria, hypouricemia, uricosuria, hypercalciuria, nephrocalcinosis, and elevated liver enzymes without associated organomegaly. The patient did not present any growth retardation and demonstrated normal cognitive and intellectual development. Her body mass index (BMI) fell within the normal low range. Bone density assessments revealed osteopenia without osteoporosis. She reported a history of consuming a high-sugar diet during adulthood. Consequently, dietary interventions were advised to reduce sugar intake, which notably impacted liver function as evidenced by decreased transaminase levels. Extensive primary liver investigations, including liver biopsy, revealed no abnormalities despite the anticipated presence of signs indicating increased glycogen storage. The diagnosis was achieved through whole exome genetic sequencing, identifying a mutation in the SLC2A2 gene encoding GLUT2 (homozygous mutation c.372A>C), which is consistent with FBS.

At age 28, she sought consultation regarding pregnancy and preconception risk assessment. A review of the literature revealed four documented cases of pregnancy in individuals with Fanconi Bickel Syndrome (FBS), all of which culminated in successful deliveries. Her husband does not carry the same recessive genetic variant. While the possibility of having a child affected by this condition is very low, there is a 25% risk of inheriting her genetic variant and becoming a carrier. Given these reports, she was advised to proceed with pregnancy under a multidisciplinary team including obstetricians, nephrologists, dieticians, and hepatologists, to ensure optimal management of her condition and promote the best possible outcome for both the mother and the child.

Spontaneous pregnancy occurred after one year of attempting to conceive, coinciding with the initiation of investigations for potential fertility issues. Blood and urine test results just before conceiving were compatible with her disease related findings including glycosuria, proteinuria, normal kidney function tests, normal electrolytes in blood (Na, K, Ca, Ph, Cl, Mg), very low uric acid levels in blood (1.5 mg/dl) with high fractional excretion of uric acid, a normal CBC, normal hemoglobin A1c (HgA1c) (5.3%), normal thyroid function tests, mild hyperlipidemia according to the lipid profile (cholesterol=218, triglycerides=80, HDL=59, LDL=140, nonHDL=159 mg/dl), and mildly elevated transaminases (AST=42, ALT=82 IU/l).

The first trimester of pregnancy was uneventful with routine monitoring. The baseline laboratory findings were consistent with her known disease manifestations, including glycosuria, mild proteinuria, low uric acid levels, and mildly elevated transaminases. Given her chronic kidney disease and proteinuria exceeding 300 mg/24 h, she was classified as high risk, prompting the initiation of aspirin therapy.

In the second trimester, the patient presented with metabolic complications of proximal tubulopathy, including normal anion gap metabolic acidosis secondary to bicarbonaturia. To address this, sodium bicarbonate supplementation was initiated and titrated in escalating doses to maintain normal bicarbonate levels appropriate for pregnancy. Additionally, she was started on vitamin D supplementation, as proximal tubulopathy is thought to reduce 1α-hydroxylase activity, impairing the activation of vitamin D. To compensate for this deficiency, she was prescribed alfacalcidol (α-D3). Multivitamin supplementation was also introduced to support overall maternal and fetal health. A dietician guided carbohydrate intake to optimize glucose metabolism. Proteinuria increased during pregnancy due to pregnancy-related hemodynamic changes, including increased plasma volume and intraglomerular pressure, which may further exacerbate proteinuria. Close monitoring is essential, as a significant increase in proteinuria may signal the need for therapeutic interventions to mitigate potential complications such as worsening renal function, hypertension, or adverse pregnancy outcomes.

At 30 weeks, the patient developed impaired fasting glucose (IFG) and postprandial hyperglycemia, prompting the initiation of low-dose basal insulin Detemir (Levemir), in conjunction with her disease-specific dietary regimen. To avoid exposing the patient to a high sugar load (100 g), we opted against the oral glucose tolerance test, instead relying on continuous blood glucose monitoring by an electronic glucometer to guide insulin dose adjustments on the basis of glucose fluctuations. However, under this regimen, the patient experienced an episode of subclinical hypoglycemia, with glucose levels recorded at 69 mg/dL, necessitating Detemir dosage adjustments.

At 34 weeks, she developed intrahepatic cholestasis of pregnancy (ICP), with elevated bile salts (>50 mol/L) and triglycerides (>700 mg/dL). High levels postprandial bile salts were also measured (117 mol/L) in one instance. Consequently, therapeutic intervention involving ursodeoxycholic acid was initiated, yielding symptomatic relief and subsequently, the concentration of bile salts decreased to 23,7 mol/L. Given the very high triglyceride levels, fibrate therapy was initiated to further alleviate ICP symptoms and reduce the risk of pancreatitis. Owing to the severity of ICP, which is associated with a 3% risk of late intrauterine demise (IUD), the fetus was placed under intensive monitoring. However, elevated lipid levels were detected in the third trimester and persisted, yielding cholesterol levels exceeding 340 mg/dl and triglycerides above 1900 mg/dl, without clinically observed complications. The serum calcium, phosphate, and magnesium levels remained stable, with hypercalciuria detected only in the first trimester.

Her kidney function test was still normal during pregnancy with decreasing creatinine levels, as expected, with hyperfiltration during pregnancy, and proteinuria slightly increased toward the third trimester. Urine cultures were performed without any evidence of urinary tract infections. The level of alfa fetoprotein was measured once during the second trimester and was within the normal limits (5.8) similar to the levels before conception. Pancreatic enzymes, including lipase and amylase were also measured within the normal range, with the lowest levels observed in the late third trimester.

Urine analysis revealed hypercalciuria in the first trimester only. Serum calcium and phosphor levels were normal during the three trimesters. While very low blood uric acid levels were observed in the first trimester, the levels reached low normal ranges during the third trimester. Blood magnesium levels were within the normal range before conception and during the three trimesters. At 36 weeks, the obstetric team recommended delivery, but the patient declined. However, at 37 weeks and 1 day, labor was induced, leading to the vaginal delivery of a healthy female newborn (2785 g) without complications. The newborn exhibited no hypoglycemia or respiratory distress syndrome. Postpartum monitoring revealed a return of proteinuria and lipid levels to baseline. Detailed blood test results before, during pregnancy and shortly after delivery are provided in Table 1.

Table 1 Laboratory Findings Before Conception, During Pregnancy and After Delivery

This case represents a comprehensive analysis of laboratory and clinical data pertaining to a pregnancy experienced by a 29-year-old female afflicted with a mild form of FBS. It is distinctive in several aspects. This is the first instance within the literature to document notable elevations in lipid profile parameters in association with FBS syndrome during pregnancy beyond the described levels in normal pregnancies with a return to baseline after delivery. Lipid levels during pregnancy and the magnitude of these changes during pregnancy are influenced by many factors, including prepregnancy lipid levels, BMI, age, diet, and ethnicity.^14–16 In early normal pregnancy, the lipid profile can be disrupted, with slightly decreased levels in the first trimester and increased levels from the second trimester until the end of term. Total cholesterol and LDL-C levels increased by approximately 30–50% while triglycerides increased by approximately 50–100% and HDL-C levels and apolipoprotein A1 (apoA1) increased by 20–40% from early pregnancy onward with a plateau at approximately 20–24 weeks.^17,18

Despite presenting with predominant hepatic and renal clinical manifestations and laboratory findings indicative of dysglycemia and glucose storage anomalies, it delineates the occurrence of gestational diabetes mellitus (GDM), with prompts the initiation of insulin therapy, albeit amid debate due to the patient’s presentation of a normal HbA1c percentage and the high risk of hypoglycemia in such cases. Notably, this is the second reported case complicated by ICP, necessitating therapeutic interventions. Electrolytes in urine were not detected in any of the previous cases during pregnancy. Water and electrolytes replacement on the basis of urinary losses, vitamin D and multivitamin supplementation and nutritional management with slowly absorbed carbohydrates contributed to a fairly good prognosis of the disease.

Literature Review

Information regarding childbearing status and pregnancy outcomes in individuals with FBS is limited. A published literature search using the terms “FBS” “pregnancy” and “reproduction” in the PubMed database yielded only four reports documenting reproduction among individuals with FBS. Another additional case recently reported was noted during the preparation of this manuscript. The details previously reported pregnancy cases are provided in Table 2.

Table 2 Reported Cases of Pregnancy in FBS Syndrome

1. Pena et al. A 31-year-old woman with diet-controlled GDM delivered a healthy boy via C-section. There are no records of laboratory tests conducted during pregnancy.¹⁹
2. Ke˛dzierska et al reported a 31-year-old patient with FBS, which was complicated by renal failure requiring dialysis and postprandial hyperglycemia treated with a diet alone. Delivery by C-section was due to the presence of polyhydramnios.²⁰
3. Carli et al reported a 38-year-old patient with FBS who experienced an uncomplicated pregnancy. She delivered a healthy girl newborn at 40 weeks and 3 days of gestation via normal delivery.²¹
4. DeLeon et al described a 22-year-old patient who was diagnosed with FBS, and who exhibited rickets as a manifestation of her condition. This report aimed to elucidate the rationale behind the anesthetic choices employed during cesarean section, which significantly contributed to achieving a successful outcome.²²
5. The latest report describes a 27-year-old patient with a previous history of pregnancy with a miscarriage at age 22 and a term cesarean section at age 23 (not published). This focused on continuous glucose monitoring-derived glycemic patterns and specific guidance for cornstarch therapy and medical nutrition therapy for the treatment of FBS-associated dysglycemia, allowing the avoidance of insulin therapy.²³

Discussion

While the symptoms associated with FBS do not appear to hinder reproduction in affected individuals,²¹ these case reports document instances of successful pregnancies in six affected women. They underscore a range of clinical considerations relevant to individuals affected by the syndrome, emphasizing the crucial need to consider data and procedures to ensure optimal fetal and maternal outcomes in this complex disease.

The manifestations of FBS during pregnancy can vary and may not always result in complications. Therefore, a collaborative approach involving obstetric care and the expertise of various specialists before, during, and after pregnancy is strongly recommended, ensuring vigilant surveillance for complications such as GDM, cholestasis, deteriorating renal function, nephrolithiasis, urinary tract infections related to constant glycosuria and increasing the risk of premature birth, and obstetrical complication delivery outcomes.

GDM, a characteristic feature inherent to the disease that may be exacerbated during pregnancy due to hormonal alterations associated with the physiological state, is the most prevalent complication among the patients under consideration. Postprandial hyperglycemia serves as the primary indicator of GDM, notwithstanding the presence of normal levels of HbA1c.

To date, there is a lack of empirical evidence suggesting that elevated postprandial glycemia in mothers influences fetal development. Given the presence of normal HgA1c levels alongside a minor elevation in fasting glucose, we advocate managing this phenomenon through dietary interventions emphasizing the consumption of slowly absorbed carbohydrates. Additionally, the judicious use of insulin therapy, mainly short-acting types (postprandial effects), is recommended, particularly in cases where glycemic control is challenging, to mitigate the risk of induced hypoglycemia.

Two of the mentioned pregnant patients with FBS were complicated by ICP, successfully treated with drugs and delivered after 37 weeks of gestation. The ICP incidence rate is between 0.2 and 2% of all pregnancies,²⁴ varies with ethnicity and geographic distribution, and is higher among patients with chronic liver disease.^25,26 ICP arises from disruptions in biliary lipid secretion, potentially influenced by the actions of endogenous steroids. Several authors have suggested that ICP is probably associated with the overproduction of some sulfated progesterone metabolites.^27,28 It is not possible to explain this phenomenon just by considering the presented data; however, the high 17-hydroxyprogesterone levels measured in our case may indicate the anticipated effect of pregnancy hormones in FBS. These findings highlight the need to closely monitor symptoms and signs of worsening hepatic disease in FBS patients during late pregnancy. To date, this is the first report documenting notable elevations in lipid profile parameters beyond the described levels in normal pregnancies with a return to baseline after delivery.

As a result of the physiological state, renal plasma flow and the glomerular filtration rate increase during pregnancy. Increased urinary excretion of calcium, uric acid, sodium, and oxalate, all of which are lithogenic.^29,30 Most patients with FBS suffer from polydipsia and polyuria and develop chronic kidney disease later in life, nephrocalcinosis or bilateral nephrolithiasis, resulting mainly from hypercalciuria, which is the leading cause.³¹ Hyperphosphaturia, as an accompanying entity, can exacerbate this problem. One of the patients presented with urolithiasis or kidney stone symptoms, during pregnancy. Complicated nephrolithiasis can occur before conception, and renal function deteriorates during pregnancy, resulting in the need for dialysis treatment.

Conclusion

This report highlights the complexity of managing rare inherited metabolic disorder affecting multiple organ systems and extends the current knowledge about FBS treatment approaches during pregnancy. Close laboratory monitoring, water and electrolyte replacement on the basis of urinary loss, vitamin D and multivitamin supplementation, nutritional management with slowly absorbed carbohydrates and judicious and close control of insulin administration contributed to a fairly good prognosis of the disease. Given its multisystem involvement, effective management requires a structured, multidisciplinary approach involving endocrinologists, hepatologists, nephrologists, geneticists, and dietitians. Awareness of inherited metabolic disorders like FBS and its early recognition are especially important for appropriate genetic counseling, risk stratification, and monitoring of metabolic status in both the mother and fetus.³² This report underscores the importance of a comprehensive prenatal evaluation and careful postpartum monitoring, enabling timely initiation of dietary modifications and supportive treatment to optimize growth and metabolic balance.

Abbreviations

FBS, Fanconi–Bickel syndrome; GLUT2, glucose transporter membrane protein-2; ARPTH, autosomal recessive proximal tubulopathy and hypercalciuria; MRI, magnetic resonance imaging; BMI, body mass index; IFG, impaired fasting glucose; IC, intrahepatic cholestasis of pregnancy; IUD, intrauterine demise; GFR, glomerular filtration rate; AST, aspartate aminotransferase; ALT, alanine aminotransferase; ALKP, alkaline phosphatase; GGT, gamma-glutamyltransferase; LDH, lactate dehydrogenase; CPK, creatine phosphokinase; HDL, high-density lipoprotein; WBC, white blood cell; INR, international normalized ratio; PPG, postprandial glucose; FG, fasting glucose; TSH, thyroid stimulating hormone; DHEA, dehydroepiandrosterone; apoA1, apolipoprotein A1; GDM, gestational diabetes mellitus; DXA, dual-energy X-ray absorptiometry; HgA1c, hemoglobin A1c; G-tube, gastric tube; CGM, continuous glucose monitoring; MNT, medical nutrition therapy.

Ethical Approval

Only one case was presented not requiring approval from our Ethics Committee (Galilee Medical Centre, Nahariyah). Clinical trial number is not applicable.

Consent

Informed written consent has been obtained from the patient for publication of her clinical details.

Disclosure

The authors report no conflicts of interest in this work.

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