Progressive external ophthalmoplegia and vision and hearing loss in a patient with mutations in POLG2 and OPA1 - PubMed (original) (raw)

Case Reports

doi: 10.1001/archneurol.2007.9.

Susanna Clark, Emanuela Garelli, Guido Davidzon, Steven A Moore, Randy H Kardon, Rachelle J Bienstock, Matthew J Longley, Michelangelo Mancuso, Purificación Gutiérrez Ríos, Michio Hirano, William C Copeland, Salvatore DiMauro

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Case Reports

Progressive external ophthalmoplegia and vision and hearing loss in a patient with mutations in POLG2 and OPA1

Silvio Ferraris et al. Arch Neurol. 2008 Jan.

Abstract

Objective: To describe the clinical features, muscle pathological characteristics, and molecular studies of a patient with a mutation in the gene encoding the accessory subunit (p55) of polymerase gamma (POLG2) and a mutation in the OPA1 gene.

Design: Clinical examination and morphological, biochemical, and molecular analyses.

Setting: Tertiary care university hospitals and molecular genetics and scientific computing laboratory.

Patient: A 42-year-old man experienced hearing loss, progressive external ophthalmoplegia (PEO), loss of central vision, macrocytic anemia, and hypogonadism. His family history was negative for neurological disease, and his serum lactate level was normal.

Results: A muscle biopsy specimen showed scattered intensely succinate dehydrogenase-positive and cytochrome-c oxidase-negative fibers. Southern blot of muscle mitochondrial DNA showed multiple deletions. The results of screening for mutations in the nuclear genes associated with PEO and multiple mitochondrial DNA deletions, including those in POLG (polymerase gamma gene), ANT1 (gene encoding adenine nucleotide translocator 1), and PEO1, were negative, but sequencing of POLG2 revealed a G1247C mutation in exon 7, resulting in the substitution of a highly conserved glycine with an alanine at codon 416 (G416A). Because biochemical analysis of the mutant protein showed no alteration in chromatographic properties and normal ability to protect the catalytic subunit from N-ethylmaleimide, we also sequenced the OPA1 gene and identified a novel heterozygous mutation (Y582C).

Conclusion: Although we initially focused on the mutation in POLG2, the mutation in OPA1 is more likely to explain the late-onset PEO and multisystem disorder in this patient.

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Figures

Figure 1

Figure 1

Histochemical stains for hematoxylin-eosin (A), succinate dehydrogenase (SDH) (B), and cytochrome-c oxidase (COX) (C and D) of serial cross sections of muscle from the patient. In A and C, 2 fibers (labeled 1 and 2) show increased eosinophilia and COX negativity; and in B and D, 2 fibers (labeled 1 and 2) show increased SDH stain and lack of COX activity.

Figure 2

Figure 2

Electropherogram of the POLG2 (gene encoding the accessory subunit [p55] of polymerase γ) sequence showing the heterozygous G1247C transversion in exon 7 (arrow). A, normal sequence; B, patient’s sequence.

Figure 3

Figure 3

Coomassie-stained gel of the purified recombinant G416A-p55 protein.

Figure 4

Figure 4

G416A-p55 protects p140 against inactivation by _N_-ethylmaleimide (NEM). DNA polymerase activity was measured as described in the “DNA Polymerase Assays” subsection of the “Methods” section, except that 2-mercaptoethanol was excluded. Reactions contained 75-mmol/L sodium chloride, 8.0 ng (58 fmol) of p140 either alone or in the presence of 6.3 ng (116 fmol) of wild-type p55 or G416A-p55 and the indicated amounts of NEM.

Figure 5

Figure 5

G416A-p55 stimulates processive DNA synthesis of polymerase γ (polγ). Primer extension reactions were performed as described in the “DNA Polymerase Assays” subsection of the “Methods” section. Reactions contained p140 catalytic subunit (lanes 1–6), wild-type (WT) p55 (lanes 3 and 4), G416A-p55 (lanes 5–6), and singly primed M13 DNA. Activity was measured at 0-mmol/L sodium chloride (odd lanes) or 150-mmol/L sodium chloride (even lanes). Lane 0 had no enzyme. Reaction products were resolved by denaturing polyacrylamide gel electrophoresis. The arrow marks the unextended 35-mer primer. The marker 100 indicates the number of nucleotides synthesized past the primer. +; indicates present; −, absent.

Figure 6

Figure 6

Position of the G416A side chain on the ribbon structure of the human accessory subunit in one monomer within the p55 dimer. The ribbon drawing was generated with Swiss PDB viewer from Protein Data Bank file 2G4C. The inset is an expanded view of the structure around G416 in domain 3.

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References

    1. DiMauro S, Bonilla E. Mitochondrial encephalomyopathies. In: Engel AG, Franzini-Armstrong C, editors. Myology. Vol. 2. New York, NY: McGraw-Hill Co; 2004. pp. 1623–1662.
    1. Rowland LP. Mitochondrial encephalomyopathies: lumping, splitting, and melding. In: Schapira AHV, DiMauro S, editors. Mitochondrial Disorders in Neurology. Oxford, England: Butterworth-Heinemann; 1994. pp. 116–129.
    1. Zeviani M, Servidei S, Gellera C, Bertini E, DiMauro S, DiDonato S. An autosomal dominant disorder with multiple deletions of mitochondrial DNA starting at the D-loop region. Nature. 1989;339(6222):309–311. - PubMed
    1. Spinazzola A, Zeviani M. Disorders of nuclear-mitochondrial intergenomic signaling. Gene. 2005;354:162–168. - PubMed
    1. Kaukonen J, Juselius JK, Tiranti V, et al. Role of adenine nucleotide translocator 1 in mtDNA maintenance. Science. 2000;289(5480):782–785. - PubMed

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