Kidney and Metabolic Phenotypes in Glycogen Storage Disease Type-I Patients

Hepatic ketone body regulation of renal gluconeogenesis

OBJECTIVES

During fasting, liver pivotally regulates blood glucose levels through glycogenolysis and gluconeogenesis. Kidney also produces glucose through gluconeogenesis. Gluconeogenic genes are transactivated by fasting, but their expression patterns are chronologically different between the two organs. We find that renal gluconeogenic gene expressions are positively correlated with the blood β-hydroxybutyrate concentration. Thus, we herein aim to investigate the regulatory mechanism and its physiological implications.

METHODS

Gluconeogenic gene expressions in liver and kidney were examined in hyperketogenic mice such as high-fat diet (HFD)-fed and ketogenic diet-fed mice, and in hypoketogenic PPARα knockout (PPARα-/-) mice. Renal gluconeogenesis was evaluated by rise in glycemia after glutamine loading in vivo. Functional roles of β-hydroxybutyrate in the regulation of renal gluconeogenesis were investigated by metabolome analysis and RNA-seq analysis of proximal tubule cells.

RESULTS

Renal gluconeogenic genes were transactivated concurrently with blood β-hydroxybutyrate uprise under ketogenic states, but the increase was blunted in hypoketogenic PPARα-/- mice. Administration of 1,3-butandiol, a ketone diester, transactivated renal gluconeogenic gene expression in fasted PPARα-/- mice. In addition, HFD-fed mice showed fasting hyperglycemia along with upregulated renal gluconeogenic gene expression, which was blunted in HFD-fed PPARα-/- mice. In vitro experiments and metabolome analysis in renal tubular cells showed that β-hydroxybutyrate directly promotes glucose and NH3 production through transactivating gluconeogenic genes. In addition, RNA-seq analysis revealed that β-hydroxybutyrate-induced transactivation of Pck1 was mediated by C/EBPβ.

CONCLUSIONS

Our findings demonstrate that β-hydroxybutyrate mediates hepato-renal interaction to maintain homeostatic regulation of blood glucose and systemic acid-base balance through renal gluconeogenesis regulation.

Clinical and biochemical footprints of inherited metabolic diseases. XIV. Metabolic kidney diseases

Kidney disease is a global health burden with high morbidity and mortality. Causes of kidney disease are numerous, extending from common disease groups like diabetes and arterial hypertension to rare conditions including inherited metabolic diseases (IMDs). Given its unique anatomy and function, the kidney is a target organ in about 10% of known IMDs, emphasizing the relevant contribution of IMDs to kidney disease. The pattern of injury affects all segments of the nephron including glomerular disease, proximal and distal tubular damage, kidney cyst formation, built-up of nephrocalcinosis and stones as well as severe malformations. We revised and updated the list of known metabolic etiologies associated with kidney involvement and found 190 relevant IMDs. This represents the 14th of a series of educational articles providing a comprehensive and revised list of metabolic differential diagnoses according to system involvement.

Glycogen storage disease type I: Genetic etiology, clinical manifestations, and conventional and gene therapies

Glycogen storage disease type I (GSDI) is an inherited metabolic disorder characterized by a deficiency of enzymes or proteins involved in glycogenolysis and gluconeogenesis, resulting in excessive intracellular glycogen accumulation. While GSDI is classified into four different subtypes based on molecular genetic variants, GSDIa accounts for approximately 80%. GSDIa and GSDIb are autosomal recessive disorders caused by deficiencies in glucose-6-phosphatase (G6Pase-α) and glucose-6-phosphate-transporter (G6PT), respectively. For the past 50 years, the care of patients with GSDI has been improved following elaborate dietary managements. GSDI patients currently receive dietary therapies that enable patients to improve hypoglycemia and alleviate early symptomatic signs of the disease. However, dietary therapies have many limitations with a risk of calcium, vitamin D, and iron deficiency and cannot prevent long-term complications, such as progressive liver and renal failure. With the deepening understanding of the pathogenesis of GSDI and the development of gene therapy technology, there is great progress in the treatment of GSDI. Here, we review the underlying molecular genetics and the current clinical management strategies of GSDI patients with an emphasis on promising experimental gene therapies.

Clinical and genetic spectrum of GSD type 6 in Korea

BACKGROUND

Glycogen storage disease type VI (GSD VI) is a rare disease in which liver glycogen metabolism is impaired by mutations in the glycogen phosphorylase L (PYGL). This study aimed to examine the clinical features, genetic analyses, and long-term outcomes of patients with GSD VI in Korea.

METHODS

From January 2002 to November 2022, we retrospectively reviewed patients diagnosed with GSD VI using a gene panel at Seoul National University Hospital. We investigated the clinical profile, liver histology, molecular diagnosis, and long-term outcomes of patients with GSD VI.

RESULTS

Five patients were included in the study. The age at onset was 18-30 months (median, 21 months), and current age was 3.7-17 years (median, 11 years). All patients showed hepatomegaly, elevated liver transaminase activity, and hypertriglyceridaemia. Hypercholesterolaemia and fasting hypoglycaemia occurred in 60% and 40% of patients, respectively. Ten variants of PYGL were identified, of which six were novel: five missense (p.[Gly607Val], p.[Leu445Pro], p.[Gly695Glu], p.[Val828Gly], p.[Tyr158His]), and one frameshift (p.[Arg67AlafsTer34]). All patients were treated with a high-protein diet, and four also received corn starch. All patients showed improved liver function tests, hypertriglyceridaemia, hepatomegaly, and height z score.

CONCLUSIONS

The GSD gene panel is a useful diagnostic tool for confirming the presence of GSD VI. Genetic heterogeneity was observed in all patients with GSD VI. Increased liver enzyme levels, hypertriglyceridaemia, and height z score in patients with GSD VI improved during long-term follow-up.

Treatment of the Neutropenia Associated with GSD1b and G6PC3 Deficiency with SGLT2 Inhibitors

Glycogen storage disease type Ib (GSD1b) is due to a defect in the glucose-6-phosphate transporter (G6PT) of the endoplasmic reticulum, which is encoded by the SLC37A4 gene. This transporter allows the glucose-6-phosphate that is made in the cytosol to cross the endoplasmic reticulum (ER) membrane and be hydrolyzed by glucose-6-phosphatase (G6PC1), a membrane enzyme whose catalytic site faces the lumen of the ER. Logically, G6PT deficiency causes the same metabolic symptoms (hepatorenal glycogenosis, lactic acidosis, hypoglycemia) as deficiency in G6PC1 (GSD1a). Unlike GSD1a, GSD1b is accompanied by low neutrophil counts and impaired neutrophil function, which is also observed, independently of any metabolic problem, in G6PC3 deficiency. Neutrophil dysfunction is, in both diseases, due to the accumulation of 1,5-anhydroglucitol-6-phosphate (1,5-AG6P), a potent inhibitor of hexokinases, which is slowly formed in the cells from 1,5-anhydroglucitol (1,5-AG), a glucose analog that is normally present in blood. Healthy neutrophils prevent the accumulation of 1,5-AG6P due to its hydrolysis by G6PC3 following transport into the ER by G6PT. An understanding of this mechanism has led to a treatment aimed at lowering the concentration of 1,5-AG in blood by treating patients with inhibitors of SGLT2, which inhibits renal glucose reabsorption. The enhanced urinary excretion of glucose inhibits the 1,5-AG transporter, SGLT5, causing a substantial decrease in the concentration of this polyol in blood, an increase in neutrophil counts and function and a remarkable improvement in neutropenia-associated clinical signs and symptoms.

Outcome of liver transplantation in hepatic glycogen storage disease: A systematic review and meta-analysis

INTRODUCTION

Liver transplantation (LT) is the choice of therapeutic option for end-stage hepatic GSD patients; however, reports about the long-term outcome of LT in these patients have remained controversial.

METHODS

We performed a systematic review and meta-analysis of observational studies published until Dec 31, 2021, that investigated the long-term outcome of LT in hepatic GSD patients. A literature search in the MEDLINE/PubMed, EMBASE,Cochrane Library, Scopus and Web of Science Core Collection databases was performed.

RESULTS

14 studies with 210 patients were included in our analysis. As the results showed, the pooled proportion of GSD patients with complications after liver transplant (e.g., hemorrhagic shock, biliary complications, tacrolimus encephalopathy, chronic hepatitis, hepatic artery thrombosis, hepatic adenoma, sepsis, liver dysfunction, chronic rejection, acute cellular rejection, and CMV infection) was 27.7% (95% CI: 20.42-35.67) without heterogeneity (I²  = 24.04%), as calculated by the random-effect model. The pooled proportion of GSD patients with complications related to GSD after LT, including HCC (Hepatocellular carcinoma), renal complication, muscle problems, delayed menarche, persistent neutropenia, pneumonitis, renal failure, and hepatic adenoma was 22.2% (95% CI: 7.97-40.01) with high heterogeneity (I²  = 82.47%). Subgroup analysis including the age of patients (adult/pediatric), duration of follow-up, and type of donor was conducted to investigate the resources of heterogeneity.

CONCLUSION

According to our investigation and review analysis, most GSD patients showed significant outcome improvement after liver transplantation. Overall, our findings showed an excellent outcome of liver transplantation in GSD patients; however, it needs further investigations to be confirmed.

Glycogen storage disease type 1a in the Ohio Amish

Glycogen storage disease type 1a (GSD1a) is an inborn error of glucose metabolism characterized by fasting hypoglycemia, hepatomegaly, and growth failure. Late complications include nephropathy and hepatic adenomas. We conducted a retrospective observational study on a cohort of Amish patients with GSD1a. A total of 15 patients cared for at a single center, with a median age of 9.9 years (range 0.25–24 years) were included. All patients shared the same founder variant in GCPC c.1039 C > T. The phenotype of this cohort demonstrated good metabolic control with median cohort triglyceride level slightly above normal, no need for continuous overnight feeds, and a higher quality of life compared to a previous GSD cohort. The most frequent complications were oral aversion, gross motor delay, and renal hyperfiltration. We discuss our unique care delivery at a single center that cares for Amish patients with inherited disorders.

Understanding the role of SGLT2 inhibitors in glycogen storage disease type Ib: the experience of one UK centre

BACKGROUND

Glycogen storage disease type Ib (GSD Ib) is a severe disorder of carbohydrate metabolism due to bi-allelic variants in SLC37A4. It is associated with neutropaenia and neutrophil dysfunction, which has recently been attributed to the accumulation of 1,5-anhydroglucitol-6-phosphate (1,5AG6P) within neutrophils. Treatment with sodium-glucose co-transporter-2 (SGLT2) inhibitors, such as empagliflozin, is a novel therapy that reduces 1,5-anhydroglucitol (1,5AG) in plasma.

RESULTS

We report our experience in treating 8 paediatric GSD Ib patients with empagliflozin with a cumulative treatment time greater than 12 years. Treatment with a median dose of 5 mg (0.22 mg/kg height weight) of empagliflozin resulted in improvement in bowel health, growth, and laboratory parameters. Plasma 1,5AG levels reduced by a median of 78%. Baseline 1,5AG levels in our cohort were higher than in adult patients with GSD Ib. Hypoglycaemia on empagliflozin treatment occurred in 50% of our cohort.

CONCLUSION

We report the largest single centre cohort of GSD Ib patients treated with empagliflozin to date. Treatment with SGLT2 inhibitors is a novel and favourable treatment option for neutropaenia and neutrophil dysfunction in GSD Ib. We suggest a low starting dose of empagliflozin with careful titration due to the risk of hypoglycaemia. The interpretation of 1,5AG levels and their role in treatment monitoring is yet to be established, and requires ongoing research.

A Systematic Review investigating the Effectiveness of Exercise training in Glycogen Storage Diseases

Introduction

Glycogen storage diseases (GSDs) are rare inborn errors of carbohydrate metabolism typically with skeletal muscle and liver involvement. In those with skeletal muscle involvement, the majority display symptoms of exercise intolerance which can cause profound exercise limitation and impair everyday living and quality of life (QoL). There are no curative treatments for GSDs, thus therapeutic options, such as exercise training, are aimed at improving QoL by alleviating signs and symptoms. In order to investigate the effectiveness of exercise training in adults with GSDs, we systematically reviewed the literature.

Methods

In this review we conducted searches within SCOPUS and MEDLINE to identify potential papers for inclusion. These papers were independently assessed for inclusion and quality by two authors. We identified 23 studies which included aerobic training, strength training or respiratory muscle training in patients with McArdles (n = 41) and Pompe disease (n = 139).

Results

In McArdle disease, aerobic exercise training improved aerobic capacity (VO2 peak) by 14-111% with further benefits to functional capacity and well-being. Meanwhile, strength training increased muscle peak power by 100-151% and reduced disease severity. In Pompe disease, a combination of aerobic and strength training improved VO2 peak by 9-10%, muscle peak power by 64%, functional capacity and well-being. Furthermore, respiratory muscle training (RMT) improved respiratory muscular strength [maximum inspiratory pressure (MIP) increased by up to 65% and maximum expiratory pressure (MEP) by up to 70%], with additional benefits shown in aerobic capacity, functional capacity and well-being.

Conclusion

This adds to the growing body of evidence which suggests that supervised exercise training is safe and effective in improving aerobic capacity and muscle function in adults with McArdle or Pompe disease. However, the literature base is limited in quality and quantity with a dearth of literature regarding exercise training in other GSD subtypes.

DBS Screening for Glycogen Storage Disease Type 1a: Detection of c.648G>T Mutation in G6PC by Combination of Modified Competitive Oligonucleotide Priming-PCR and Melting Curve Analysis

Glycogen storage disease type Ia (GSDIa) is an autosomal recessive disorder caused by glucose-6-phosphatase (G6PC) deficiency. GSDIa causes not only life-threatening hypoglycemia in infancy, but also hepatocellular adenoma as a long-term complication. Hepatocellular adenoma may undergo malignant transformation to hepatocellular carcinoma. New treatment approaches are keenly anticipated for the prevention of hepatic tumors. Gene replacement therapy (GRT) is a promising approach, although early treatment in infancy is essential for its safety and efficiency. Thus, GRT requires screening systems for early disease detection. In this study, we developed a screening system for GSDIa using dried blood spots (DBS) on filter paper, which can detect the most common causative mutation in the East-Asian population, c.648G>T in the G6PC gene. Our system consisted of nested PCR analysis with modified competitive oligonucleotide priming (mCOP)-PCR in the second round and melting curve analysis of the amplified products. Here, we tested 54 DBS samples from 50 c.648G (wild type) controls and four c.648T (mutant) patients. This system, using DBS samples, specifically amplified and clearly detected wild-type and mutant alleles from controls and patients, respectively. In conclusion, our system will be applicable to newborn screening for GSDIa in the real world.