ISSN 2398-2977      

Muscle: glycogen branching enzyme deficiency (GBED)

pequis

Synonym(s): GBED


Introduction

  • An autosomal recessive genetic disease of Quarterhorses and related breeds; genetic testing suggests one particular line is implicated.
  • Cause: lack of the glycogen branching enzyme leads to a lack of glucose available for metabolic processes.
  • Signs: sudden death, weakness, seizures, contracted tendons in neonatal foals.
  • Diagnosis: genetic testing, elevated liver and muscle enzymes, histopathology on necropsy samples.
  • Treatment: none.
  • Prognosis: results in late-term abortion or death of foals by a few months of age.

Pathogenesis

Etiology

  • Similar to the rare inherited glycogenoses disease in humans known as glycogen storage disease type IV (GSD-IV).
  • Inherited as a simple autosomal recessive condition on equine chromosome 26.
  • Heterozygotes are carriers only and do not show any clinical signs.
  • Disease is fatal for homozygotes.

Predisposing factors

General
  • Quarterhorse.
  • Line-breeding.

Pathophysiology

  • Glucose is the bodys main source of energy.
  • In order to store energy, the body converts glucose into glycogen, which is arranged in a tree-like structure with branches.
  • The glycogen branching enzyme is the protein required for this process to occur correctly.
  • When the body needs energy, it breaks off one of the branches and converts it into glucose.
  • A lack of the glycogen branching enzyme leads to very long, unbranched glucose chains being stored.
  • Without the branches, there are very few areas that can be broken off and used for energy.
  • Without energy, muscles become weak, the brain can seizure, or the heart may stop beating, all of which can lead to death of the foal.

Timecourse

  • Some foals are stillborn up to 3 months prior to expected due date.
  • Some foals have lived up until 2 months of age.
  • To date, all foals confirmed to have GBED have died or were euthanized due to weakness.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Tay K H S, Akman H O, Chung W K et al (2004) Fatal infantile neuromuscular presentation of glycogen storage disease type IV.  Neuromuscular Disorders 14, 253-260 PubMed.
  • Ward T L,Valberg S J, Lear T L et al (2003) Genetic mapping of GBE1 and its association with glycogen storage disease IV in American Quarter horses. Cytogenet Genome Res 102, 201-206 PubMed.
  • Valberg S J, Ward T L, Rush B et al (2001) Glycogen branching enzyme deficiency in Quarter Horse foals. J Vet Intern Med 15, 572-580 PubMed.

Other sources of information

  • MacLeay J M (2004) Diseases of the musculoskeletal system. In: Equine Internal Medicine. Eds: Reed S, Bayley W M & Sellon D C. Elsevier, USA. pp 512.

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