Peculiar combinations of individually non-pathogenic missense mitochondrial DNA variants cause low penetrance Leber's hereditary optic neuropathy

PLoS Genet. 2018 Feb 14;14(2):e1007210. doi: 10.1371/journal.pgen.1007210. eCollection 2018 Feb.

Abstract

We here report on the existence of Leber's hereditary optic neuropathy (LHON) associated with peculiar combinations of individually non-pathogenic missense mitochondrial DNA (mtDNA) variants, affecting the MT-ND4, MT-ND4L and MT-ND6 subunit genes of Complex I. The pathogenic potential of these mtDNA haplotypes is supported by multiple evidences: first, the LHON phenotype is strictly inherited along the maternal line in one very large family; second, the combinations of mtDNA variants are unique to the two maternal lineages that are characterized by recurrence of LHON; third, the Complex I-dependent respiratory and oxidative phosphorylation defect is co-transferred from the proband's fibroblasts into the cybrid cell model. Finally, all but one of these missense mtDNA variants cluster along the same predicted fourth E-channel deputed to proton translocation within the transmembrane domain of Complex I, involving the ND1, ND4L and ND6 subunits. Hence, the definition of the pathogenic role of a specific mtDNA mutation becomes blurrier than ever and only an accurate evaluation of mitogenome sequence variation data from the general population, combined with functional analyses using the cybrid cell model, may lead to final validation. Our study conclusively shows that even in the absence of a clearly established LHON primary mutation, unprecedented combinations of missense mtDNA variants, individually known as polymorphisms, may lead to reduced OXPHOS efficiency sufficient to trigger LHON. In this context, we introduce a new diagnostic perspective that implies the complete sequence analysis of mitogenomes in LHON as mandatory gold standard diagnostic approach.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amino Acid Sequence
  • DNA, Mitochondrial / genetics*
  • Electron Transport Complex I / chemistry
  • Electron Transport Complex I / genetics
  • Epistasis, Genetic
  • Family
  • Female
  • Genes, Mitochondrial
  • Humans
  • Male
  • Models, Molecular
  • Multifactorial Inheritance*
  • Mutation, Missense*
  • NADH Dehydrogenase / chemistry
  • NADH Dehydrogenase / genetics
  • Optic Atrophy, Hereditary, Leber / genetics*
  • Pedigree
  • Penetrance*
  • Young Adult

Substances

  • DNA, Mitochondrial
  • NADH dehydrogenase subunit 4
  • MT-ND6 protein, human
  • NADH Dehydrogenase
  • NADH dehydrogenase subunit 1, human
  • Electron Transport Complex I

Grant support

This study received support from “Programma di ricerca Regione-Università 2010-2012” (PRUa1RI-2012-008 to VC), Telethon – Italy (Grant no. GGP06233 to VC), the Italian Ministry of Health (Ricerca Corrente 2016), the Italian Ministry of Education, University and Research: Progetti Futuro in Ricerca 2012 (RBFR126B8I) (to AA and AO) and Progetti Ricerca Interesse Nazionale 2012 (to AA, and AT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.