Molecular and biochemical characterisation of a novel mutation in POLG associated with Alpers syndrome

BMC Neurol. 2011 Jan 14;11:4. doi: 10.1186/1471-2377-11-4.

Abstract

Background: DNA polymerase γ (POLG) is the only known mitochondrial DNA (mtDNA) polymerase. It mediates mtDNA replication and base excision repair. Mutations in the POLG gene lead to reduction of functional mtDNA (mtDNA depletion and/or deletions) and are therefore predicted to result in defective oxidative phosphorylation (OXPHOS). Many mutations map to the polymerase and exonuclease domains of the enzyme and produce a broad clinical spectrum. The most frequent mutation p.A467T is localised in the linker region between these domains. In compound heterozygote patients the p.A467T mutation has been described to be associated amongst others with fatal childhood encephalopathy. These patients have a poorer survival rate compared to homozygotes.

Methods: mtDNA content in various tissues (fibroblasts, muscle and liver) was quantified using quantitative PCR (qPCR). OXPHOS activities in the same tissues were assessed using spectrophotometric methods and catalytic stain of BN-PAGE.

Results: We characterise a novel splice site mutation in POLG found in trans with the p.A467T mutation in a 3.5 years old boy with valproic acid induced acute liver failure (Alpers-Huttenlocher syndrome). These mutations result in a tissue specific depletion of the mtDNA which correlates with the OXPHOS-activities.

Conclusions: mtDNA depletion can be expressed in a high tissue-specific manner and confirms the need to analyse primary tissue. Furthermore, POLG analysis optimises clinical management in the early stages of disease and reinforces the need for its evaluation before starting valproic acid treatment.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Culture Techniques
  • Child, Preschool
  • DNA Polymerase gamma
  • DNA, Mitochondrial / metabolism*
  • DNA-Directed DNA Polymerase / genetics*
  • Diffuse Cerebral Sclerosis of Schilder / genetics*
  • Diffuse Cerebral Sclerosis of Schilder / metabolism
  • Fibroblasts / metabolism
  • Humans
  • Liver / metabolism
  • Male
  • Muscle, Skeletal / metabolism
  • Mutation / genetics*
  • Oxidative Phosphorylation
  • Sequence Analysis, DNA / methods

Substances

  • DNA, Mitochondrial
  • DNA Polymerase gamma
  • DNA-Directed DNA Polymerase