Glucose-6-phosphatase gene (727G-->T) splicing mutation is prevalent in Hong Kong Chinese patients with glycogen storage disease type 1a

A glycogen storage disease type 1a patient with type 2 diabetes

Background

Glycogen storage disease type 1a (GSD1a) is an inborn genetic disease caused by glucose-6-phosphatase-α (G6Pase-α) deficiency and is often observed to lead to endogenous glucose production disorders manifesting as hypoglycemia, hyperuricemia, hyperlipidemia, lactic acidemia, hepatomegaly, and nephromegaly. The development of GSD1a with diabetes is relatively rare, and the underlying pathogenesis remains unclear.

Case presentation

Here we describe a case of a 25-year-old Chinese female patient with GSD1a, who developed uncontrolled type 2 diabetes mellitus (T2DM) as a young adult. The patient was diagnosed with GSD1a disease at the age of 10 and was subsequently treated with an uncooked cornstarch diet. Recently, the patient was treated in our hospital for vomiting and electrolyte imbalance and was subsequently diagnosed with T2DM. Owing to the impaired secretory function of the patient’s pancreatic islets, liver dysfunction, hypothyroidism, severe hyperlipidemia, and huge hepatic adenoma, we adopted diet control, insulin therapy, and hepatic adenoma resection to alleviate this situation. The WES discovered compound heterozygous mutations at the exon 5 of G6PC gene at 17th chromosome in the patient, c.648G>T (p.L216 L, NM_000151.4, rs80356484) in her father and c.674T>C (p.L225 P, NM_000151.4, rs1555560128) in her mother. c.648G>T is a well-known splice-site mutation, which causes CTG changing to CTT at protein 216 and creates a new splicing site 91 bp downstream of the authentic splice site, though both codons encode leucine. c.674T>C is a known missense mutation that causes TGC to become CGC at protein 225, thereby changing from coding for leucine to coding for proline.

Conclusion

We report a rare case of GSD1a with T2DM. On the basis of the pathogenesis of GSD1a, we recommend attentiveness to possible development of fasting hypoglycemia caused by GSD and postprandial hyperglycemia from diabetes. As the disease is better identified and treated, and as patients with GSD live longer, this challenge may appear more frequently. Therefore, it is necessary to have a deeper and more comprehensive understanding of the pathophysiology of the disease and explore suitable treatment options.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01344-3.

Case Report: Glycogen Storage Disease Type Ia in a Chinese Child Treated With Growth Hormone

BACKGROUND

Glycogen storage disease type Ia is a rare metabolic disorder that leads to excessive glycogen and fat accumulation in organs, characterized by hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, puberty delay, and growth retardation. Here, we report on a patient with glycogen storage disease type Ia treated with growth hormone.

CASE PRESENTATION

A 10-year-old boy had growth retardation for 6 years, and was admitted to clarify the cause of his short stature. We found that his bone age was 5.5 years, significantly lower than his physical age, while his serum IGF-1 and IGFBP-3 were 23.30 and 1620.0 ng/mL, respectively, both lower than normal. His medical history revealed that he had suffered from steatohepatitis, hyperlipidemia, and hypoglycemia since he was 11 months of age. Whole exome sequencing (WES) showed compound heterozygous mutations in exons 2 and 5 of the glucose-6-phosphatase (G6PC) gene on chromosome 17: c.G248A (p.R83H) and c.G648T (p.L216L). The patient was finally diagnosed with GSD Ia. After growth hormone (GH) treatment and corn starch therapy for 14 months, his height significantly increased (by 13 cm). The serum IGF-1 level increased to the normal range but his lipid levels and liver function did not significantly increase.

CONCLUSION

We describe a young patient with a compound heterozygous G6PC variant in a Chinese family; his height increased significantly after growth hormone and corn starch interventions. This case emphasizes that WES is essential for early diagnosis, and that growth hormone treatment may increase the height of patients with GSD Ia safely.

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.

Ending diagnostic odyssey using clinical whole-exome sequencing (CWES)

Objectives

Most rare diseases are genetic diseases. Due to the diversity of rare diseases and the high likelihood of patients with rare diseases to be undiagnosed or misdiagnosed, it is not unusual that these patients undergo a long diagnostic odyssey before they receive a definitive diagnosis. This situation presents a clear need to set up a dedicated clinical service to end the diagnostic odyssey of patients with rare diseases.

Methods

Therefore, in 2014, we started an Undiagnosed Diseases Program in Hong Kong with the aim of ending the diagnostic odyssey of patients and families with rare diseases by clinical whole-exome sequencing (CWES), who have not received a definitive diagnosis after extensive investigation.

Results

In this program, we have shown that genetic diseases diagnosed by CWES were different from that using traditional approaches indicating that CWES is an essential tool to diagnose rare diseases and ending diagnostic odysseys. In addition, we identified several novel genes responsible for monogenic diseases. These include the TOP2B gene for autism spectrum disorder, the DTYMK gene for severe cerebral atrophy, the KIF13A gene for a new mosaic ectodermal syndrome associated with hypomelanosis of Ito, and the CDC25B gene for a new syndrome of cardiomyopathy and endocrinopathy.

Conclusions

With the incorporation of CWES in an Undiagnosed Diseases Program, we have ended diagnostic odysseys of patients with rare diseases in Hong Kong in the past 7 years. In this program, we have shown that CWES is an essential tool to end diagnostic odysseys. With the declining cost of next-generation sequencers and reagents, CWES set-ups are now affordable for clinical laboratories. Indeed, owing to the increasing availability of CWES and treatment modalities for rare diseases, precedence can be given to both common and rare medical conditions.

Predominance of the c.648G > T G6PC gene mutation and late complications in Korean patients with glycogen storage disease type Ia

BACKGROUND

Glycogen storage disease (GSD) Ia, caused by mutations in the glucose-6-phosphatase (G6PC) gene, is characterized by hepatomegaly, hypoglycemia, lactic acidosis, dyslipidemia, and hyperuricemia. This study aimed to investigate clinical and molecular features and late complications in Korean patients with GSD Ia.

RESULTS

Fifty-four Korean patients (33 males and 21 females) from 47 unrelated families, who were diagnosed with GSD Ia, based on genetic and biochemical data, between 1999 and 2017, were included in this study. The median age at diagnosis was 3.9 years (range: 5 months to 42 years), and the follow-up period was 8.0 ± 6.8 years. Most patients presented with hepatomegaly during infancy, but hypoglycemic symptoms were not predominant. Genetic analysis showed that all the patients had at least one c.648G > T allele. Homozygous c.648G > T mutations in the G6PC gene were identified in 34 families (72.3%), and compound heterozygotes with c.648G > T were found in the other families. The allele frequency of c.648G > T was 86.2% (81/94), and p.F51S, p.R83H, p.G122D, p.Y128*, p.G222R, and p.T255A were identified. Of 26 adult patients, 14 had multiple hepatic adenomas, and two were diagnosed with hepatocellular carcinoma. Thirteen patients showed renal complications, and seven patients presented gout, despite preventive allopurinol treatment. Twelve patients had osteoporosis, and two patients had pulmonary hypertension. The final heights were 157.9 cm (standard deviation score: - 3.1) in males and 157.8 cm (standard deviation score: - 0.6) in females.

CONCLUSION

In our Korean patients with GSD Ia, the most common mutation in the G6PC gene was c.648G > T, suggesting a founder effect. Because of only mild hypoglycemia, the patients tended to be diagnosed late. Thus, adult patients with GSD Ia eventually developed diverse and serious complications, which indicates a need for careful monitoring and proper management of this disease.

A patient with glycogen storage disease type Ia combined with chronic hepatitis B infection: a case report

BACKGROUND

Glycogen storage disease type I (GSD I), also known as von Gierk disease, is a metabolic disorder leading to the excessive accumulation of glycogen and fat in organs, characterized by hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, puberty delay and growth retardation, which can be indicated by height, weight, blood glucose and blood lipids.

CASE PRESENTATION

Here we present a 16-year-old male patient with GSD Ia complicated with hepatic adenoma and combined with hepatitis B. As a chronic hepatitis B patient, the patient was admitted to hospital in order to further clarify the nature of hepatic space occupancy because of suspicion of hepatocellular carcinoma. However, the imaging studies did not support hepatocellular carcinoma certainly. And by tracing his clinical history, we suggested that he might suffer from GSD I. Finally the diagnosis was confirmed by MRI (Gd-EOB-DTPA), liver biopsy and whole exome sequencing (WES). The WES discovered a homozygous point mutation at the exon 5 of G6PC gene at 17th chromosome, c.G648 T (p.L216 L, NM_000151, rs80356484). This pathogenic mutation causes CTG changing to CTT at protein 216. Though both codons encode leucine, this silent mutation creates a new splicing site 91 bp downstream of the authentic splice site. According to previous research, this mutation is a disease causal variant for GSD Ia, and has a high frequency among GSD patients in China and Japan. This patient was finally diagnosed as GSD Ia complicated with hepatic adenoma and combined with chronic hepatitis B, and received corn starch therapy immediately after GSD was suspected. After receiving corn starch therapy, the height and weight of the patient were increased, and the secondary sexual characteristics were developed, including beard, pubic hair and seminal emission. Unexpectedly, the liver adenomas were still increasing, and we did not find any cause to explain this phenomenon.

CONCLUSION

This patient was diagnosed as GSD Ia combined with chronic hepatitis B, who responded to corn starch intervention. For childhood patients with hypoglycaemia, hyperlipidemia, puberty delay and growth retardation, GSD should be considered. Gene sequencing is valuable for the quick identification of GSD subtypes.

Diagnosis and management of glycogen storage disease type I: a practice guideline of the American College of Medical Genetics and Genomics

PURPOSE

Glycogen storage disease type I (GSD I) is a rare disease of variable clinical severity that primarily affects the liver and kidney. It is caused by deficient activity of the glucose 6-phosphatase enzyme (GSD Ia) or a deficiency in the microsomal transport proteins for glucose 6-phosphate (GSD Ib), resulting in excessive accumulation of glycogen and fat in the liver, kidney, and intestinal mucosa. Patients with GSD I have a wide spectrum of clinical manifestations, including hepatomegaly, hypoglycemia, lactic acidemia, hyperlipidemia, hyperuricemia, and growth retardation. Individuals with GSD type Ia typically have symptoms related to hypoglycemia in infancy when the interval between feedings is extended to 3–4 hours. Other manifestations of the disease vary in age of onset, rate of disease progression, and severity. In addition, patients with type Ib have neutropenia, impaired neutrophil function, and inflammatory bowel disease. This guideline for the management of GSD I was developed as an educational resource for health-care providers to facilitate prompt, accurate diagnosis and appropriate management of patients.

METHODS

A national group of experts in various aspects of GSD I met to review the evidence base from the scientific literature and provided their expert opinions. Consensus was developed in each area of diagnosis, treatment, and management.

RESULTS

This management guideline specifically addresses evaluation and diagnosis across multiple organ systems (hepatic, kidney, gastrointestinal/nutrition, hematologic, cardiovascular, reproductive) involved in GSD I. Conditions to consider in the differential diagnosis stemming from presenting features and diagnostic algorithms are discussed. Aspects of diagnostic evaluation and nutritional and medical management, including care coordination, genetic counseling, hepatic and renal transplantation, and prenatal diagnosis, are also addressed.

CONCLUSION

A guideline that facilitates accurate diagnosis and optimal management of patients with GSD I was developed. This guideline helps health-care providers recognize patients with all forms of GSD I, expedite diagnosis, and minimize adverse sequelae from delayed diagnosis and inappropriate management. It also helps to identify gaps in scientific knowledge that exist today and suggests future studies.

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

Mutations in the glucose-6-phosphatase-alpha (G6PC) gene that cause type Ia glycogen storage disease

Glucose-6-phosphatase-alpha (G6PC) is a key enzyme in glucose homeostasis that catalyzes the hydrolysis of glucose-6-phosphate to glucose and phosphate in the terminal step of gluconeogenesis and glycogenolysis. Mutations in the G6PC gene, located on chromosome 17q21, result in glycogen storage disease type Ia (GSD-Ia), an autosomal recessive metabolic disorder. GSD-Ia patients manifest a disturbed glucose homeostasis, characterized by fasting hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, lactic acidemia, and growth retardation. G6PC is a highly hydrophobic glycoprotein, anchored in the membrane of the endoplasmic reticulum with the active center facing into the lumen. To date, 54 missense, 10 nonsense, 17 insertion/deletion, and three splicing mutations in the G6PC gene have been identified in more than 550 patients. Of these, 50 missense, two nonsense, and two insertion/deletion mutations have been functionally characterized for their effects on enzymatic activity and stability. While GSD-Ia is not more prevalent in any ethnic group, mutations unique to Caucasian, Oriental, and Jewish populations have been described. Despite this, GSD-Ia patients exhibit phenotypic heterogeneity and a stringent genotype-phenotype relationship does not exist.

Glucose-6-phosphatase gene mutations in 20 adult Japanese patients with glycogen storage disease type 1a with reference to hepatic tumors

BACKGROUND AND AIMS

A few cases are reported of liver neoplasms observed in patients with glycogen storage disease type 1a (GSD1a). Genetic analysis was carried out in adult Japanese patients with GSD1a and their family members, and hepatic tumors were also investigated in these patients.

METHODS

DNA was extracted from the peripheral blood lymphocytes of 20 adult patients with GSD1a and 21 family members, and mutations were detected based on the differences in the polymerase chain reaction (PCR) products of the glucose-6-phosphatase (G6Pase) gene shown by single-strand conformation polymorphism (SSCP) analysis. Actual mutations were confirmed by direct sequencing. The relationship between the occurrence of liver tumors and the clinical characteristics of the patients was also investigated.

RESULTS

Nineteen of the 20 patients were homozygous for the G727T mutation and one was a compound heterozygote for G727T plus G327A mutations. All of the 19 homozygotes for G727T had hepatomegaly, three had hepatocellular carcinoma, one had cholangiocellular carcinoma, and seven had hepatic adenoma. There were no differences between the tumor and non-tumor groups with respect to laboratory biochemical data (P > 0.05). The mean age of G727T homozygotes with hepatocellular carcinoma was 48.3 years, and that of those with hepatic adenoma was approximately 20 years younger.

CONCLUSION

The G727T mutation seems to be common among Japanese patients with GSD1a, and the discovery of one heterozygote with a combination of G727T and G327A mutations (the latter mutation is common among Chinese) by the use of polymerase chain reaction-single strand conformation polymorphism analysis gave further insight into Japanese ancestry. This is the first study of liver tumors in a large group of adult GSD1a patients with the G727T mutation. As most of the patients in our series are free from other chronic liver diseases such as viral hepatitis, other genetic and/or acquired factors may have influence on the sequel to this metabolic disease.

Molecular genetics of glycogen-storage disease type 1a in Chinese patients of Taiwan

The mutation spectrum of the glucose 6-phosphatase (G6Pase) gene in Chinese patients with type 1a glycogen-storage disease of Taiwan was studied by PCR/RFLP, temporal temperature gradient gel electrophoresis, and direct DNA sequencing methods. In addition to the two most prevalent mutations, 727G --> T (44.4%) and R83H (36.1%), that were detected by RFLP analysis, five other mutations, 341delG, 933insAA, Q104X, I341N, and H119L were identified. The frameshift mutations (341delG and 933insAA) and the nonsense mutation (Q104X) that produce truncated proteins are predicted to be disease-causing. The missense mutation, I341N, occurring in the last transmembrane domain of the ER-bound enzyme, retains a small amount of residual activity of approximately 10%. Except for R83H, the mutations have been described only in Asians. H119L, however, is of particular interest because of the essential role of the catalytic histidine of phosphohydrolase. This amino acid is believed to be involved in the formation of the phosphoryl-enzyme intermediate during catalysis. The patient who was compound heterozygous for 727G --> T and H119L mutations had essentially no G6Pase activity in her liver biopsy. This observation is consistent with the importance of H119L in catalysis.

Glycogen storage disease type Ia: frequency and clinical course in Turkish children

The aim of this study was to determine the relative frequency of type Ia in glycogen storage disease (GSD) with prominent liver involvement and to determine its clinical and laboratory findings and prognosis in Turkish children. From 1980 to 1998, 45 out of 100 GSD patients (27 male) with liver involvement had been diagnosed for type Ia. The files were retrospectively evaluated and clinical and laboratory features were documented. In addition to routine laboratory evaluations, urine albumin, calcium excretions, and plasma biotinidase activity were measured. Breast-feeding was continued in all infants. After 6 months of age, uncooked cornstarch was administered to the patients. The relative frequency of type Ia in GSD with liver involvement was 45%. The diagnosis was made in 71% of patients before 2 years of age (median 1 year). Main complaint was abdominal protruding (57.8%), and main physical finding was hepatomegaly (100%). Forty percent of the patients had growth retardation at diagnosis. Among laboratory parameters, hypertriglyceridemia (97.8%) and hypertransaminasemia (95.6%) were the most frequent findings following plasma biotinidase activity, which was elevated in all patients. Microalbuminuria was determined in 52.8% of the patients and hypercalciuria in 23.8%. Histopathological findings of the liver included fibrosis (75.6%), steatosis (37.8%), mosaicism (24.4%) and nuclear hyperglycogenation (15.6%). During follow-up period, the ratio of patients with growth retardation did not change. Transaminases were decreased in 48.7% of the patients. Although triglyceride and cholesterol levels decreased in the majority of the patients, they did not normalise. The prevalence of type Ia in GSD with prominent liver involvement was found higher than the other reports. Microalbuminuria was also higher than the previous reports.

New lessons in the regulation of glucose metabolism taught by the glucose 6-phosphatase system

The operation of glucose 6-phosphatase (EC 3.1.3.9) (Glc6Pase) stems from the interaction of at least two highly hydrophobic proteins embedded in the ER membrane, a heavily glycosylated catalytic subunit of m 36 kDa (P36) and a 46-kDa putative glucose 6-phosphate (Glc6P) translocase (P46). Topology studies of P36 and P46 predict, respectively, nine and ten transmembrane domains with the N-terminal end of P36 oriented towards the lumen of the ER and both termini of P46 oriented towards the cytoplasm. P36 gene expression is increased by glucose, fructose 2,6-bisphosphate (Fru-2,6-P2) and free fatty acids, as well as by glucocorticoids and cyclic AMP; the latter are counteracted by insulin. P46 gene expression is affected by glucose, insulin and cyclic AMP in a manner similar to P36. Accordingly, several response elements for glucocorticoids, cyclic AMP and insulin regulated by hepatocyte nuclear factors were found in the Glc6Pase promoter. Mutations in P36 and P46 lead to glycogen storage disease (GSD) type-1a and type-1 non a (formerly 1b and 1c), respectively. Adenovirus-mediated overexpression of P36 in hepatocytes and in vivo impairs glycogen metabolism and glycolysis and increases glucose production; P36 overexpression in INS-1 cells results in decreased glycolysis and glucose-induced insulin secretion. The nature of the interaction between P36 and P46 in controling Glc6Pase activity remains to be defined. The latter might also have functions other than Glc6P transport that are related to Glc6P metabolism.

Molecular Genetics of Type 1 Glycogen Storage Diseases

Glycogen storage disease type 1 (GSD-1), also known as von Gierke disease, is caused by a deficiency in the activity of the enzyme glucose-6-phosphatase (G6Pase). It is an autosomal recessive disorder characterized by hypoglycemia, hepatomegaly, kidney enlargement, growth retardation, lactic acidemia, hyperlipidemia and hyperuricemia. The disease presents with both clinical and biochemical heterogeneity consistent with the existence of two major subgroups, GSD-1a and GSD-1b, which have been confirmed at the molecular genetic level. GSD-1a, the most prevalent form, is caused by mutations in the G6Pase gene that abolish or greatly reduce enzymatic activity. The gene maps to chromosome 17q21 and encodes a microsomal transmembrane protein. Animal models of GSD-1a exist and are being exploited to delineate the disease more precisely. It has been proposed that GSD-1b is caused by a defect in the microsomal glucose-6-phosphate transporter. The gene responsible for GSD-1b has been mapped to chromosome 11q23 and a cDNA encoding a microsomal transmembrane protein has been identified. The function of this putative GSD-1b protein remains to be determined. These recent developments, along with newly characterized animal models of GSD-1a, are increasing our understanding of the interrelationship between the components of the G6Pase complex and type 1 glycogen storage diseases.