Leber's Hereditary Optic Neuropathy–Specific Heteroplasmic Mutation m.14495A>G Found in a Chinese Family

Abstract

Purpose Leber's hereditary optic neuropathy (LHON) is a mitochondrial DNA (mtDNA)-associated, maternally inherited eye disease. Mutation heteroplasmy level is one of the leading causes to trigger LHON manifestation. In this study, we aimed to identify the causative mutation in a large Han Chinese family with LHON and explore the underlying pathogenic mechanism in this LHON family. Methods The whole-mtDNA sequence was amplified by long-range PCR. Mutations were subsequently identified by next-generation sequencing (NGS) and validated by Sanger sequencing. The heteroplasmy rates of those family members were determined by digital PCR (dPCR). Mitochondrial haplogroups were assigned based on mtDNA tree build 17. Results The m.14495A>G mutation was identified as causative due to its higher heteroplasmy level (>50%) in patients than in their unaffected relatives. All mutation carriers belong to M7b1a1 and are assigned to Asian mtDNA lineage. Interestingly, our result revealed that high mtDNA copy number in carrier might prevent LHON manifestation. Conclusions This is the first report of m.14495A>G mutation in Asian individuals with LHON. Our study shows that dPCR technology can provide more reliable results in mutation heteroplasmy assay and determination of the cellular mtDNA content, making it a potentially promising tool for clinical precise diagnosis of LHON. Furthermore, our results also add evidence to the opinion that higher mtDNA content may protect mutation carriers from LHON. Translational Relevance dPCR can be used for the assessment of LHON disease, and a new genetic-based diagnostic strategy has been proposed for LHON patients with the m.14495A>G mutation.

Heteroplasmy Rates of the m.14495A>G variant in MT-ND6 May Not Predict the Phenotype of LHON

“…The authors propose a heteroplasmy threshold of 50% above which carriers of the m.14495A>G manifest clinically 1. We ask why the two individuals, IV-7 and V-5, did not manifest clinically despite heteroplasmy rates more than 50%.…”

“…With interest, we read the article by Li et al1 about a Han Chinese family with Leber's hereditary optic neuropathy (LHON) due to the secondary LHON mtDNA variant m.14495A>G in MT-ND6 . We have the following comments and concerns.…”

“…We do not agree with the conclusions “that heteroplasmy levels of LHON mutations in blood cells can be used as a diagnostic indicator of LHON risk.”1 According to Table 1 of the article,1 the correlation between heteroplasmy and risk of developing LHON is poor. Two patients with heteroplasmy rates higher than 50% did not manifest clinically.…”

“…We ask why the two individuals, IV-7 and V-5, did not manifest clinically despite heteroplasmy rates more than 50%. We ask if heteroplasmy rates were determined only with digital polymerase chain reaction 1. Application of an alternative technique is crucial not to generate false-positive results.…”

Whole Mitochondrial Genome Analysis in Serbian Cases of Leber’s Hereditary Optic Neuropathy

“…Secondary mutations have been studied as modifiers for phenotypic expression of LHON by acting in synergy with the primary mutations. In addition, intermediate LHON mutations might act independently of the occurrence of primary mutations [ 28 , 29 , 30 ]. Other mitochondrial variants such as m.3394T>C, m.4435A>G, m.5601C>T and m.15951A>G have been found to be strongly associated with positive 11778G>A LHON disease [ 31 , 32 , 33 , 34 ].…”