Mitochondrial 13513G>A Mutation With Low Mutant Load Presenting as Isolated Leber's Hereditary Optic Neuropathy Assessed by Next Generation Sequencing

Abstract

Objective: Mitochondrial 13513G>A mutation presenting as isolated Leber's hereditary optic neuropathy (LHON) without any extraocular pathology has not been reported in literature. We herein evaluate the clinical characteristics and heteroplasmy of m.13513G>A mutation manifesting as isolated LHON.Methods: Seven members of a Chinese family were enrolled in this study. All subjects underwent detailed systemic and ophthalmic examinations. Mitochondrial DNA in their blood was assessed by targeted PCR amplifications, next generation sequencing (NGS), and pyrosequencing. One hundred of blood samples from ethnic-matched healthy volunteers were tested by NGS and pyrosequencing as normal controls.Results: Isolated LHON without any other ocular or extraocular pathology was identified in a 16 year old patient in this family. Heteroplasmic m.13513G>A mutation was detected by NGS of the full mtDNA genome in the patient with mutant load of 33.56%, and of 26% 3 months and 3 years after the onset of LHON, respectively. No m.13513G>A mutation was detected in all his relatives by NGS. Pyrosequencing revealed the mutant load of m.13513G>A mutation of the LHON patient, his mother, father and sister were 22.4, 1.9, 0, and 0%, respectively. None of 100 healthy control subjects was detected to harbor m.13513G>A mutation either by NGS or by pyrosequencing of the full mt DNA genome.Conclusions: We first report m.13513G>A mutation with low mutant load presenting as isolated LHON. NGS of the full mitochondrial DNA genome is highly recommended for LHON suspects when targeted PCR amplification for main primary point mutations of LHON was negative.

Clinical Reasoning: A 31-Year-Old Man With Sequential Vision Loss

“…12 Significant mitochondrial impairment leads to the increased formation of reactive oxygen species and reduced adenosine triphosphate production culminating in cell apoptosis. 11 This case illustrates the importance of whole-genome mitochondrial sequencing when initial screening for the 3 common mtDNA pathogenic variants is negative.…”

“…[8][9][10] Genetic mutation load (i.e., heteroplasmy) is an important factor in the risk of vision loss in LHON related to a phenotypic expression threshold, but not necessarily to illness severity or multiorgan involvement. 11 The ND5 protein, a hydrophobic polypeptide, is one of 45 subunits (38 of which are nuclear DNA encoded and 7 mtDNA encoded) of complex I within the mitochondrial electron transport chain. The ND5 gene is the largest of the mtDNA encoded complex I genes.…”

Long read mitochondrial genome sequencing using Cas9-guided adaptor ligation

“…The G1642A variant was identified in 2 patients with MELAS (de Coo et al, 1998; Taylor et al, 1996). The G13513A variant has been reported in association with a variety of clinical presentations including MELAS, Leigh disease and isolated optic neuropathy (Shanske et al, 2008; Sun et al, 2021). Given the patient’s clinical presentation, it was concluded that the G13513A variant was likely responsible for her disease, with the G1642A variant possibly contributory, however the relationship between the variants is unknown.…”

MELAS with multiple stroke‐like episodes due to the variant m.13513G>A in MT‐ND5

“…A further argument in favor of the pathogenicity is that the amino acid change Asp>Asn at position D393 may lead to loss of the quinine reactive site and subsequently to reduced activity of the oxidative phosphorylation. 12 …”

“…The low heteroplasmy rate does not exclude pathogenicity as only a mildly affected tissue was investigated. A further argument in favor of the pathogenicity is that the amino acid change Asp>Asn at position D393 may lead to loss of the quinine reactive site and subsequently to reduced activity of the oxidative phosphorylation 12 …”