Abstract for presentation at 11th International Congress of Human Genetics

Mutations in NDUFAF1, encoding a complex I assembly factor, are a novel cause of mitochondrial disease

  • Miss Canny Sugiana, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
  • Mr Christopher Dunning, Department of Biochemistry, La Trobe University, Melbourne, Australia
  • Mr Michael Lazarou, Department of Biochemistry, La Trobe University, Melbourne, Australia
  • Dr Matthew McKenzie, Department of Biochemistry, La Trobe University, Melbourne, Australia
  • Ms Angela Connelly, Department of Biochemistry, La Trobe University, Melbourne, Australia
  • Dr Janice Fletcher, Department of Genetic Medicine, Adelaide Women's and Children's Hospital, Adelaide, Australia
  • Dr David Thorburn, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
  • A/Prof Michael Ryan, Department of Biochemistry, La Trobe University, Melbourne, Australia

    • Complex I is the largest of five enzyme complexes comprising the mitochondrial respiratory chain. To date, pathogenic mutations have been identified in 16 conserved subunit genes and one molecular chaperone which is a paralogue of a Complex I subunit. Since subunit gene mutations probably account for only about half of all patients, more assembly factor genes must await identification. Two Complex I assembly factors were identified by studies of Complex I biogenesis in Neurospora crassa, namely CIA30 and CIA84. In humans, putative homologues are encoded by the NDUFAF1 and PTCD1 genes but no pathogenic mutations have been identified and there are few data to confirm the roles of these proteins.
    We confirmed that the NDUFAF1 protein is mitochondrial and localized to the matrix in association with the inner membrane. Blue Native PAGE and western blotting show that NDUFAF1 is present in several high molecular weight complexes that migrate differently from the mature respiratory complexes. Co-immunoprecipitation shows that a number of Complex I subunits are associated with NDUFAF1, however only a small percentage of the total amount of these subunits are found in association with NDUFAF1.
    We identified a patient with cardiomyopathy, developmental delay and lactic acidosis whose fibroblasts and EBV-lymphoblasts showed marked reduction of NDUFAF1 protein levels. Sequencing identified two novel heterozygous mutations in NDUFAF1. One mutation was of maternal origin and predicted the substitution of a highly conserved threonine residue by proline. The second mutation is of paternal origin and causes a splicing defect that results in a larger stable mRNA species but apparently results in an unstable or dysfunctional protein. Currently we are performing functional correction studies and cloning of individual alleles to confirm the pathogenicity of both mutations. We conclude that NDUFAF1 encodes a complex I assembly factor and is a novel cause of complex I deficiency.

    Conference Organiser - ICMS Pty Ltd