Abstract
Purpose :
Reports from populations of different geographic backgrounds show that about 90% percent of individuals with Leber hereditary optic neuropathy (LHON) harbour one of the three (primary) mitochondrial DNA (mtDNA) point mutations: m.3460G>A (MT-ND1), m.11778G>A (MT-ND4) or m.14484T>C (MT-ND6). The purpose of this study was to screen the whole mitochondrial genome of LHON patients negative for these three common mtDNA mutations to investigate the role of other mtDNA variants in the pathogenesis of this blinding optic neuropathy.
Methods :
Forty-one individuals who were clinically suspected to have LHON were recruited from the Neuro-Ophthalmology Clinic (Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India). A comprehensive neuro-ophthalmic examination, including slit lamp examination, indirect ophthalmoscopy and visual field perimetry was performed. Targeted re-sequencing using next-generation sequencing (NGS) on the HiSeqX Ten platform (Illumina, San Diego, California) was performed using a 2×150bp paired-end setting. The reads were aligned to the human mitochondrial genome sequence (hg19). The variants were filtered using VARIMAT tool (v.2.3.9) and haplogroup analysis was performed using haplogrep 2 tool (v2.0).
Results :
Whole mitochondrial genome sequencing of 41 clinically suspected cases of LHON revealed a total of 1,594 variants of which 869 variants were present in the coding region, and 582 were synonymous and 287 were non-synonymous variants. We have identified secondary mtDNA variants reported in mitomap in 12 individuals (12/41, 29%) with variants in MTND1 being the most common (7/41, 17%). Control screening for the m.4216T>C and m.9966G>A variants was conducted on 25 unrelated healthy individuals. The majority of individuals belonged to haplogroup M (n= 23). None of the controls were positive for m.9966G>A, but m.4216 T>C was identified in 2 controls. We plan to screen additional controls in order to further investigate the pathogenic status of the m.4216T>C and m.9966G>A variants.
Conclusions :
Our study of a well-characterized Indian LHON cohort negative for the three primary mtDNA mutations has revealed a number of secondary mtDNA variants that should be considered in the evaluation of optic atrophy cases. The MTND1 subunit gene could be a mutational hotspot for LHON in the Indian population.
.
This is a 2021 ARVO Annual Meeting abstract.