The Phenotypic and Genetic Spectrum of Glycogen Storage Disease Type VI.

Glycogen storage disease type VI (GSD VI) is an autosomal recessive disorder of glycogen metabolism due to mutations in the glycogen phosphorylase gene (PYGL), resulting in a deficiency of hepatic glycogen phosphorylase. We performed a systematic literature review in order to collect information on the clinical phenotypes and genotypes of all published GSD VI patients and to compare the data to those for GSD IX, a biochemically and clinically very similar disorder caused by a deficiency of phosphorylase kinase. A total of 63 genetically confirmed cases of GSD VI with clinical information were identified (median age: 5.3 years). The age at presentation ranged from 5 weeks to 38 years, with a median of 1.8 years. The main presenting symptoms were hepatomegaly and poor growth, while the most common laboratory findings at initial presentation comprised elevated activity of liver transaminases, hypertriglyceridemia, fasting hypoglycemia and postprandial hyperlactatemia. Liver biopsies (n = 37) showed an increased glycogen content in 89.2%, liver fibrosis in 32.4% and early liver cirrhosis in 10.8% of cases, respectively. No patient received a liver transplant, and one successful pregnancy was reported. Our review demonstrates that GSD VI is a disorder with broad clinical heterogeneity and a small number of patients with a severe phenotype and liver cirrhosis. Neither clinical nor laboratory findings allow for a differentiation between GSD VI and GSD IX. Early biochemical markers of disease severity or clear genotype phenotype correlations are missing. Given the overall benign and unspecific phenotype and the need for enzymatic or genetic analyses for confirmation of the diagnosis, GSD VI is likely underdiagnosed. With new treatment approaches in sight, early, pre-symptomatic diagnosis, especially with respect to hepatic cirrhosis, will become even more important.

Glycogen storage disease type VI with a novel PYGL mutation: Two case reports and literature review.

RATIONALE: Glycogen storage disease (GSD) type VI is a rare disease caused by the inherited deficiency of liver phosphorylase. PATIENT CONCERNS: The proband, a 61-month-old Chinese boy, manifested intermittent hematochezia, growth retardation, hepatomegaly, damage of liver function, mild hypoglycemia, and hyperlactatemia. The other patient was a 107-month-old Chinese girl with growth retardation, hepatomegaly, mild hypoglycemia, and hyperlactatemia. In order to further confirm the diagnosis, we conducted a liver biopsy and detected blood samples for their gene using IDT exon chip capture and high-throughput sequencing. DIAGNOSES: According to the clinical symptoms, physical examination, laboratory examinations, liver biopsy, and the genetic test finding, the 2 patients were diagnosed GSD VI. INTERVENTIONS: They were treated mainly with uncooked cornstarch. OUTCOMES: There were 2 mutations of PYGL gene in this pedigree. c.2467C>T (p. Q823X) and c.2178-2A>C occurred both in the proband and his second sister. LESSONS: As a novel mutation, c.2178-2A>C enriches the mutation spectrum of PYGL gene. The different degrees of elevated lactate is an unusual phenotype in GSD VI patients. It is not clear if this is caused by the new mutation of c. 2178-2A > C. Long-term complications remains to be observed.

Liver histology in children with glycogen storage disorders type VI and IX.

BACKGROUND: Glycogen storage diseases (GSD) type VI and IX are caused by liver phosphorylase system deficiencies and the two types are clinically indistinguishable. AIM: As the role of liver biopsy is increasingly questioned, we aim to assess its current value in clinical practice. METHODS: We retrospectively reviewed children with diagnosis of GSD VI and IX at a paediatric liver centre between 2001 and 2018. Clinical features, molecular analysis and imaging were reviewed. Liver histology was reassessed by a single histopatologist. RESULTS: Twenty-two cases were identified (9 type VI, 9 IXa, 1 IXb and 3 IXc). Features at presentation were hepatomegaly (95%), deranged AST (81%), short stature (50%) and failure to thrive (4%). Liver biopsy was performed in 19 patients. Fibrosis varied in GSD IXa with METAVIR score between F1-F3 and ISHAK score of F2-F5. METAVIR score was F2-F3 in GSD VI and F3-F4 in GSD IXc. Hepatocyte glycogenation, mild steatosis, lobular inflammatory activity and periportal copper binding protein staining were also demonstrated. CONCLUSIONS: Although GSD VI and IX are considered clinically mild, chronic histological changes of varying severity could be seen in all liver biopsies. Histopathological assessment of the liver involvement is superior to biochemical parameters, but definitive classification requires a mutational analysis.

Novel PYGL mutations in Chinese children leading to glycogen storage disease type VI: two case reports.

BACKGROUND: PYGL mutations can cause liver phosphorylase deficiency, resulting in a glycogenolysis disorder, namely, glycogen storage disease (GSD) VI. The disease is rarely reported in the Chinese population. GSD VI is mainly characterized in untreated children by hepatomegaly, growth retardation and elevated liver transaminases. CASE PRESENTATION: In this study, we report two GSD VI patients with growth retardation and abnormal liver function. There was no obvious hepatomegaly for one of them. Whole exome sequencing (WES) combined with copy number variation analysis was performed. We found a novel homozygous gross deletion, c.1621-258_2178-23del, including exons 14-17 of PYGL in patient 1. The exons 14-17 deletion of PYGL resulted in an in-frame deletion of 186 amino acids. Compound heterozygous mutations of PYGL were identified in patient 2, including a novel missense mutation c.1832C > T/p.A611V and a recurrent nonsense mutation c.280C > T/p.R94X. After treatment with uncooked cornstarch (UCS) 8 months for patient 1 and 13 months for patient 2, the liver transaminases of both patients decreased to a normal range and their stature was improved. However, patient 1 still showed mild hypertriglyceridemia. CONCLUSIONS: We describe two GSD VI patients and expand the spectrum of PYGL mutations. Patient 1 in this study is the first GSD VI case that showed increased transaminases without obvious hepatomegaly due to a novel homozygous gross deletion of PYGL identified through WES.

A novel mutation (G233D) in the glycogen phosphorylase gene in a patient with hepatic glycogen storage disease and residual enzyme activity.

We identified a novel mutation in the glycogen phosphorylase gene (PGYL) in a Chinese patient with glycogen storage disease (GSD) type VI. The patient presented with gross hepatomegaly since the age of two without history of any hypoglycemic attack. Otherwise, he was largely asymptomatic. Liver tissue enzyme assays revealed a mild deficiency of total glycogen phosphorylase. Both PGYL and PHKA2 genes were sequenced. The patient was homozygous of a missense mutation G233D in PGYL. This location forms a hairpin turn secondary structure and the small glycine residue is completely conserved in all the orthologous proteins from Escherichia coli to mammals. This is the sixth reported mutation of this form of GSD.

[Differential diagnosis of glycogenoses]. / Differentsial'naia diagnostika glikogenozov.

Different types of hepatic, muscular, and generalized forms of glycogen stogare disease, a hereditary disease caused by glycogen metabolism disorders, are analysed. The clinical and biochemical features of these diseases are described. The data on enzyme defects and methods for their detection in different types of glycogenoses as well as on the prevalence of the disease in different countries are presented.