The variable clinical phenotype of liver glycogen synthase deficiency

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.

A patient with glycogen storage disease type 0 and a novel sequence variant in GYS2: a case report and literature review

Glycogen storage disease type 0 (GSD0) is an autosomal recessive disorder caused by a sequence variant in the GYS2 gene, leading to decreased or absent activity of hepatic glycogen synthase. With a frequency of less than 1 in 1,000,000 individuals, GSD0 represents only around 1% of all glycogen storage disease cases but it might be underrecognized. A 13-month-old girl of reportedly unrelated parents presented with a decreased level of consciousness, twitching in her left cheek, and munching. During a fasting test, hyperketotic hypoglycemia was found. A novel homozygous GYS2 gene sequence variant p.Thr445Arg was later confirmed by next-generation gene sequencing. After establishing a cornstarch- and protein-rich diet, the hypoglycemic episodes subsided and the patient’s neurocognitive development was normal. To date, only 39 patients with 24 disease-causing gene variants have been identified in GSD0, and we review their characteristics. Because of the heterogeneous phenotypes, GSD0 is an underdiagnosed disorder. In patients with hyperketotic hypoglycemia and postprandial hyperglycemia, GYS2 gene analysis should be performed.

Novel GYS2 mutations in a Japanese patient with glycogen storage disease type 0a

Background

Glycogen storage disease type 0a (GSD 0a), caused by GYS2 mutations, has a broad phenotypic spectrum, mostly associated with hypoglycemia. This disease has been characterized by the inability to store glycogen in the liver, leading to no hepatomegaly. Although the prevention of hypoglycemia has been considered the first therapeutic goal, the long-term complications remain unclear. In addition, few studies summarized clinical or biochemical features or examined genotype-phenotype correlation.

Case presentation

A 4-year-old Japanese boy was admitted to our hospital because of hypoglycemia. We suspected GSD 0a based on recurrent irritability episodes before feeding, fasting ketotic hypoglycemia, postprandial hyperglycemia/hyperlactatemia, and no hepatomegaly. Mutation analyses revealed novel mutations (p.His610fs and deletion of exons 8-10) in the GYS2 gene. At 5 years old, his growth and development are normal. Fasting symptoms and hypoglycemia remain controlled by dietary management.

Review of literature

We summarized the clinical and biochemical features of 33 patients with GSD 0a and 27 different mutations in the GYS2 gene. Nonspecific fasting symptoms (lethargy, drowsiness, nausea, and irritability) were found in 39% of patients, whereas 41% were asymptomatic. All patients had a combination of fasting ketotic hypoglycemia and postprandial hyperglycemia/hyperlactatemia. Hepatomegaly and hepatic steatosis were observed in 12% and 73% of patients. There was no genotype-phenotype correlation in patients with GSD 0a.

Conclusion

This is a clinical report of a Japanese GSD 0a patient with novel GYS2 mutations and a review of cases. As secondary hepatic disorders may occur due to postprandial hyperglycemia, the treatment's ultimate goal is to prevent both hypoglycemia and hyperglycemia.

[Case of diagnostics of a rare form of glycogen disease]

Differential diagnosis of hypoglycemic syndrome remains an urgent problem in Pediatrics. In this article, a case of glycogen storage disease (BNG) type 0 is described in the boy, which is undoubtedly a rare pathology, which makes it difficult to diagnose this form of glycogenosis. In this description, the case of type 0 BNG is caused by a mutation in the GYS2 gene encoding the hepatic isoform of glycogen synthase. This form of the disease is usually asymptomatic in infancy. However, it can be suspected in the case when the refusal of night feeding causes certain difficulties due to the hungry ketotic hypoglycemia that occurs in the child. The first clinical symptoms appear in early childhood with the inclusion of a more varied diet in the child, increasing the intervals between meals. Symptoms of the disease are primarily caused by hypoglycemia. It should be noted that, despite the low levels of glycemia, most children do not have any mental development disorders, since the increase in the level of ketone bodies in the blood plasma provides the brain with an alternative source of energy.

PERSISTENT ASYMPTOMATIC SEVERE HYPOGLYCAEMIA DUE TO TYPE 0A GLYCOGENOSIS - GENERAL AND ORO-DENTAL ASPECTS

Background

Type 0 glycogenosis is a genetic metabolic disorder characterized by the absence of glycogen synthesis of hepatic synthase and hence of liver glycogen stores in normal amounts. It is an extremely rare condition.

Case study

This case is a 5-year and 11-month-old female child with asymptomatic severe hypoglycemia in the last two years. During the admission and afterwards, an extensive panel of paraclinical and imaging investigations was carried out to diagnose and document the case, which led to the specific genetic test. The result was positive for 2 heterozygous mutations in the GYS2 gene (hepatic glycogen synthase), the p.547C> T mutation was pathogenic (class 1) and c.465del, frameshift likely pathogenic (class 2). In order to integrate the clinical picture of patients with this condition and to establish potential correlations regarding the specific aspects with the general development and the phenotype, the oro-dental status was investigated.

Conclusion

The investigations showed a positive correlation with literature data in several respects: low stature, hypoglycemia with hyperketonemia but normal plasma lactate, postprandial and contradictory hyperglycemia, delayed bone development, etc. Oro-buco-maxillary aspects showed a slight delay in the dental eruption. Dietary therapy and stricter dental care and additional prophylaxis are required.

A novel mutation in the glycogen synthase 2 gene in a child with glycogen storage disease type 0

Background

Glycogen storage disease type 0 is an autosomal recessive disease presenting in infancy or early childhood and characterized by ketotic hypoglycemia after prolonged fasting and postprandial hyperglycemia and hyperlactatemia. Sixteen different mutations have been identified to date in the gene which encodes hepatic glycogen synthase, resulting in reduction of glycogen storage in the liver.

Case Presentation

Biochemical evaluation as well as direct sequencing of exons and exon-intron boundary regions of the GYS2 gene were performed in a patient presenting fasting hypoglycemia and postprandial hyperglycemia and her parents. The patient was found to be compound heterozygous for one previously reported nonsense mutation (c.736 C>T; R243X) and a novel frameshift mutation (966_967delGA/insC) which introduces a stop codon 21 aminoacids downstream from the site of the mutation that presumably leads to loss of 51% of the COOH-terminal part of the protein. The glycemia and lactatemia of the parents after an oral glucose tolerance test were evaluated to investigate a possible impact of the carrier status on the metabolic profile. The mother, who presented a positive family history of type 2 diabetes, was classified as glucose intolerant and the father, who did not exhibit metabolic changes after the glucose overload, had an antecedent history of hypoglycemia after moderate alcohol ingestion.

Conclusion

The current results expand the spectrum of known mutations in GYS2 and suggest that haploinsufficiency could explain metabolic abnormalities in heterozygous carriers in presence of predisposing conditions.