Journal of Inherited Metabolic Disease

, 30:722

High frequency of missense mutations in glycogen storage disease type VI

Authors

    • Academic Unit of Child HealthUniversity of Sheffield
  • J. Taybert
    • Department of Metabolic Diseases, Endocrinology and DiabetologyThe Children’s Memorial Health Institute
  • M. P. Champion
    • Department of Paediatric Metabolic MedicineEvelina Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust
  • V. Layet
    • Unité de GénétiqueHôpital Flaubert
  • P. Heinz-Erian
    • Department of PediatricsInnsbruck Medical University
  • A. Dalton
    • Sheffield Molecular Genetics ServiceSheffield Children’s NHS Foundation Trust
  • M. S. Tanner
    • Academic Unit of Child HealthUniversity of Sheffield
  • E. Pronicka
    • Department of Metabolic Diseases, Endocrinology and DiabetologyThe Children’s Memorial Health Institute
  • M. J. Sharrard
    • Paediatric MedicineSheffield Children’s NHS Foundation Trust
Original Article

DOI: 10.1007/s10545-007-0499-9

Cite this article as:
Beauchamp, N.J., Taybert, J., Champion, M.P. et al. J Inherit Metab Dis (2007) 30: 722. doi:10.1007/s10545-007-0499-9

Summary

Deficiency of liver glycogen phosphorylase in glycogen storage disease (GSD) type VI results in a reduced ability to mobilize glucose from glycogen. Six mutations of the PYGL gene, which encodes the liver isoform of the enzyme, have been identified in the literature. We have characterized eight patients from seven families with GSD type VI and identified 11 novel PYGL gene defects. The majority of the mutations were missense, resulting in the substitution of highly conserved residues. These could be grouped into those that were predicted to affect substrate binding (p.V456M, p.E673K, p.S675L, p.S675T), pyridoxal phosphate binding (p.R491C, p.K681T), or activation of glycogen phosphorylase (p.Q13P) or that had an unknown effect (p.N632I and p.D634H). Two mutations were predicted to result in null alleles, p.R399X and [c.1964_1969inv6;c.1969+1_+4delGTAC]. Only 7 of the 23 (30%) reported PYGL alleles carry nonsense, splice site or frameshift mutations compared to 68–80% of affected alleles of the highly homologous muscle glycogen phosphorylase gene, PYGM, that underlie McArdle disease. There was heterogeneity in the clinical symptoms observed in affected individuals. These varied from hepatomegaly and subclinical hypoglycaemia, to severe hepatomegaly with recurrent severe hypoglycaemia and postprandial lactic acidosis. We conclude that deficiency of liver glycogen phosphorylase is predominantly the result of missense mutations affecting enzyme activity. There are no common mutations and the severity of clinical symptoms varies significantly.

Copyright information

© SSIEM and Springer 2007