Mutant POLG2 disrupts DNA polymerase gamma subunits and causes progressive external ophthalmoplegia.
DNA polymerase gamma (pol gamma ) is required to maintain the genetic integrity of the 16,569-bp human mitochondrial genome (mtDNA). Mutation of the nuclear gene for the catalytic subunit of pol gamma (POLG) has been linked to a wide range of mitochondrial diseases involving mutation, deletion, and depletion of mtDNA. We describe a heterozygous dominant mutation (c.1352G-->A/p.G451E) in POLG2, the gene encoding the p55 accessory subunit of pol gamma , that causes progressive external ophthalmoplegia with multiple mtDNA deletions and cytochrome c oxidase (COX)-deficient muscle fibers. Biochemical characterization of purified, recombinant G451E-substituted p55 protein in vitro revealed incomplete stimulation of the catalytic subunit due to compromised subunit interaction. Although G451E p55 retains a wild-type ability to bind DNA, it fails to enhance the DNA-binding strength of the p140-p55 complex. In vivo, the disease most likely arises through haplotype insufficiency or heterodimerization of the mutated and wild-type proteins, which promote mtDNA deletions by stalling the DNA replication fork. The progressive accumulation of mtDNA deletions causes COX deficiency in muscle fibers and results in the clinical phenotype.
Longley
Matthew J
MJ
Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
Clark
Susanna
S
Yu Wai Man
Cynthia
C
Hudson
Gavin
G
Durham
Steve E
SE
Taylor
Robert W
RW
Nightingale
Simon
S
Turnbull
Douglass M
DM
Copeland
William C
WC
Chinnery
Patrick F
PF