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Analysis of mutant DNA polymerase γ in patients with mitochondrial DNA depletion
Author(s) -
Taanman JanWillem,
Rahman Shamima,
Pagnamenta Alistair T.,
Morris Andrew A.M.,
BitnerGlindzicz Maria,
Wolf Nicole I.,
Leonard James V.,
Clayton Peter T.,
Schapira Anthony H.V.
Publication year - 2009
Publication title -
human mutation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 162
eISSN - 1098-1004
pISSN - 1059-7794
DOI - 10.1002/humu.20852
Subject(s) - biology , mitochondrial dna , genetics , polymerase , microbiology and biotechnology , mutation , dna polymerase , gene , missense mutation , mutant
We studied six unrelated children with depletion of mitochondrial DNA (mtDNA). They presented with Leigh syndrome, infantile hepatocerebral mtDNA depletion syndrome, or Alpers‐Huttenlocher syndrome. Several genes have been implicated in mtDNA depletion. Screening of candidate genes indicated that all six patients were compound heterozygous for missense mutations in the gene for the catalytic subunit of DNA polymerase γ ( POLG ). Three of the identified mutations, c.3328C>T (p.H1110Y), c.3401A>G (p.H1134R), and c.3406G>A (p.E1136K), have not been reported earlier. To investigate the functional consequences of the mutations, we carried out a series of biochemical assays in cultured fibroblasts. These studies revealed that fibroblast cultures from the patients with infantile hepatocerebral mtDNA depletion syndrome progressively lost their mtDNA during culturing, whereas fibroblast cultures from patients presenting with Leigh syndrome or Alpers‐Huttenlocher syndrome had reduced but stable levels of mtDNA. DNA polymerase γ activity was below the normal range in all patient cultures, except for one; however, this culture showed low levels of the heterodimeric enzyme and poor DNA polymerase γ processivity. Parental fibroblast cultures had normal catalytic efficiency of DNA polymerase γ, consistent with the observation that all carriers are asymptomatic. Thus, we report the first patient with Leigh syndrome caused by POLG mutations. The cell culture experiments established the pathogenicity of the identified POLG mutations and helped to define the molecular mechanisms responsible for mtDNA depletion in the patients' tissues. The assays may facilitate the identification of those patients in whom screening for POLG mutations would be most appropriate. Hum Mutat 0, 1–8, 2008. © 2008 Wiley‐Liss, Inc.