Identification of novel mitochondrial mutations in Leber’s hereditary optic neuropathy

[摘要] Purpose: To screen mitochondrial DNA(mtDNA) variations in Leber hereditary optic neuropathy (LHON). Methods: Ten LHON patients were selectedfrom neuro-ophthalmology clinics of All India Institute of MedicalSciences (AIIMS), New Delhi, India. Clinical evaluation includedslit-lamp biomicroscopy, fundus examination, and neuroimaging. DNA wasisolated from whole blood samples. The entire coding region of themitochondrial genome was amplified by PCR in ten patients and 20controls. The full mtDNA genome except D-loop was sequenced. Allsequences were analyzed against mitochondrial reference sequenceNC_012920. Results: MtDNA sequencing revealed atotal of 30 nucleotide variations in the ten LHON patients and 29 inthe 20 controls. Of 30 changes, 30.00% (9/30) were nonsynonymous, andthe remaining 70.00% (21/30) were synonymous. In controls, a total offive changes were nonsynonymous. Out of the total 14 nonsynonymouschanges observed in cases and controls, four (p.A52T in nicotinamideadenine dinucleotide [NADH] dehydrogenase [ND1] protein; p.L128Q inND2; p.W48R in ATPase6; p.R340H in ND4 protein) were pathogenic. Fourpatients were positive for either of pathogenic changes. In total,16.66% (5/30) variations were novel out of which 40.00% (2/5) werenonsynonymous. All novel variations were submitted to the GenBankdatabase, and accession numbers were obtained. Primary LHON mutationsin complex I genes have been considered a hallmark feature of LHONpatients, and primary LHON mutations were present in two cases in thisstudy. Mutations in complex I genes (ND genes) account for 50%–90% ofLHON pedigrees in different ethnic pedigrees. In this study the highestnumbers of changes were also present in complex I genes (46.66%; 14/30)followed by complex IV (30.00%; 9/30), complex III (16.66%; 5/30), andthen complex V (6.66%; 2/30). Complex I had 5/30 (16.66%) nonsynonymouschanges, complex III had 1/30 (3.33%), complex IV had 1/30 (3.33%), andcomplex V had 2/30 (6.66%) nonsynonymous changes. Nonsynonymousmutations in cytochrome c oxidase (COX) genes have been reportedpreviously in LHON patients. Nonsynonymous mtDNA variations mayadversely affect the respiratory chain and impair the oxidativephosphorylation (OXPHOS) pathway, resulting in low ATP production andelevated reactive oxygen species (ROS) levels, which cause oxidativestress. It has previously been reported that oxidative stress (OS)leads to oxidative damage of cellular macromolecules, such asmitochondrial and nuclear DNA, proteins, and lipids along with energydepletion and a local imbalance of calcium homeostasis, resulting inneuronal degeneration. OS is the underlying etiology in several oculardiseases and also plays an essential role in LHON. Conclusions: A total of five novel mtDNAvariations were identified in this study. Nonsynonymous mtDNAvariations may adversely affect the respiratory chain and impair theOXPHOS pathway, resulting in low ATP production and elevated ROSlevels. OS further damages both nuclear and mtDNA. This preliminarystudy describes mtDNA sequence variations in a relatively small numberof LHON patients of north Indian ethnic origin. However, these resultsshould be confirmed in other populations. Early diagnosis of mtDNAvariations and prompt anti-oxidant administration in these cases maydelay OS-induced injury to retinal ganglion cells (RGCs) and henceimprove visual prognosis.

[学科分类] 生物化学/生物物理