title: Novel MTND1 mutations cause isolated exercise intolerance, complex I deficiency and increased assembly factor expression.
abstract: Complex I (CI) is the largest of the five multi-subunit complexes constituting the human oxidative phosphorylation (OXPHOS) system. Seven of its catalytic core subunits are encoded by mitochondrial DNA (ND (NADH dehydrogenase)1-6, ND4L (NADH dehydrogenase subunit 4L)), with mutations in all seven having been reported in association with isolated CI deficiency. We investigated two unrelated adult patients presenting with marked exercise intolerance, persistent lactic acidaemia and severe muscle-restricted isolated CI deficiency associated with sub-sarcolemmal mitochondrial accumulation. Screening of the mitochondrial genome detected novel mutations in the MTND1 (NADH dehydrogenase subunit 1) gene, encoding subunit of CI [Patient 1, m.3365T>C predicting p.(Leu20Pro); Patient 2, m.4175G>A predicting p.(Trp290*)] at high levels of mitochondrial DNA heteroplasmy in skeletal muscle. We evaluated the effect of these novel MTND1 mutations on complex assembly showing that CI assembly, although markedly reduced, was viable in the absence of detectable ND1 signal. Real-time PCR and Western blotting showed overexpression of different CI assembly factor transcripts and proteins in patient tissue. Together, our data indicate that the mechanism underlying the expression of the biochemical defect may involve a compensatory response to the novel MTND1 gene mutations, promoting assembly factor up-regulation and stabilization of respiratory chain super-complexes, resulting in partial rescue of the clinical phenotype.
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Grainne S
authors.initials: GS
authors.lastname: Gorman
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Blakely
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Hue-Tran
authors.initials: HT
authors.lastname: Hornig-Do
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Helen A L
authors.initials: HA
authors.lastname: Tuppen
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Greaves
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Langping
authors.initials: L
authors.lastname: He
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Angela
authors.initials: A
authors.lastname: Baker
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Gavin
authors.initials: G
authors.lastname: Falkous
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Jane
authors.initials: J
authors.lastname: Newman
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Michael I
authors.initials: MI
authors.lastname: Trenell
authors.affiliation: ‡The Walton Centre NHS Foundation Trust, Liverpool L9 7LJ, U.K.
authors.forename: Bryan
authors.initials: B
authors.lastname: Lecky
authors.affiliation: §Department of Neurology, Southern General Hospital, Glasgow G51 4TF, U.K.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Petty
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Doug M
authors.initials: DM
authors.lastname: Turnbull
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Robert
authors.initials: R
authors.lastname: McFarland
authors.affiliation: *Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, U.K.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
mesh_terms: D000293:Adolescent; D004272:DNA, Mitochondrial / Q000235:genetics; D042967:Electron Transport Complex I / Q000172:deficiency*; D005080:Exercise Test / Q000379:methods; D017079:Exercise Tolerance / Q000235:genetics*; D005260:Female; D006801:Humans; D017240:Mitochondrial Myopathies / Q000201:enzymology / Q000235:genetics*; D018482:Muscle, Skeletal / Q000201:enzymology; D009154:Mutation; D009245:NADH Dehydrogenase / Q000235:genetics*; D010375:Pedigree; D055815:Young Adult
chemical_list: D004272:DNA, Mitochondrial; D042967:Electron Transport Complex I; D009245:NADH Dehydrogenase; C515075:NADH dehydrogenase subunit 1, human