Mitochondrial DNA mutation 14487T>C manifesting as Leber's hereditary optic neuropathy

Progressive myoclonic epilepsy due to rare mitochondrial ND6 mutation, m.14487T>C

Introduction

Mitochondrial diseases exhibit wide phenotypic heterogeneity, and can present as progressive myoclonic epilepsy.

Summary

We report a case of adult-onset drug-resistant epilepsy, cortical myoclonus and bilateral optic neuropathies due to m.14487T>C, a rare mitochondrial gene mutation identified on whole-genome sequencing. This mutation, which affects the NADH dehydrogenase 6 (ND6) subunit of the mitochondrial respiratory chain, is most commonly implicated in cases of infantile-onset Leigh syndrome, although a broader phenotypic spectrum including migraine with aura and progressive myoclonic epilepsy have been described. Serial MRI scans over a 2-year period demonstrated the interval development of bihemispheric stroke-like lesions. Giant somatosensory evoked potentials and short-duration myoclonic jerks with craniocaudal spread on surface electromyography were consistent with cortical myoclonus. Optical coherence tomography showed bilateral symmetric thinning of the nerve fibre layer in the papillomacular bundles.

Conclusion

Whole-genome sequencing can help to provide a definitive diagnosis for mitochondrial disease and should be considered in situations where clinical suspicion remains high despite normal genetic panels or muscle histopathology. Mitochondrial disease can present as adult-onset progressive myoclonic epilepsy, and bilateral optic neuropathies can be a striking feature of ND6 mitochondrial gene mutations. In our case, severe cortical myoclonus affecting speech and swallowing remained highly drug-resistant, however, symptomatic benefit was derived from targeted onabotulinum toxin A injections.

Smoking and alcohol, health-related quality of life and psychiatric comorbidities in Leber's Hereditary Optic Neuropathy mutation carriers: a prospective cohort study

Background

Leber’s hereditary optic neuropathy (LHON) is a rare mitochondrial disorder, characterized by acute or subacute bilateral vision loss, frequently leading to significant chronic disability, mainly in young people. The causal LHON mutations of the mitochondrial DNA have incomplete penetrance, with the highest risk of disease manifestation for male mutation carriers in the second and third decades of life. Here we evaluated smoking, alcohol drinking habits, health-related quality of life (QOL) and psychiatric comorbidities in a cohort of LHON patients and asymptomatic mutation carriers from a tertiary referral centre.

Methods

Cross-sectional analysis of the ongoing Munich LHON prospective cohort study. Participants included all LHON patients and asymptomatic LHON mutation carriers older than 16 years at baseline, who were recruited between February 2014 and June 2015 and consented to participate. General, neurological and ophthalmological investigations were performed, including validated questionnaires on smoking, alcohol drinking habits, depressive symptoms and health-related QOL.

Results

Seventy-one participants were included, 34 LHON patients (82% male) and 37 asymptomatic mutation carriers (19% male). Median age at baseline was 36 years (range 18–75 years). For LHON patients, median age at visual loss onset was 27 years (9 to 72 years). Smoking is more frequent in LHON patients than asymptomatic LHON mutation carriers, and significantly more frequent in both groups than in the general population. Sixty percent of LHON patients, who smoked at disease onset, stopped or significantly reduced smoking after visual loss onset, yet 40% of LHON patients continued to smoke at study baseline. Excessive alcohol consumption is more frequent in male LHON patients than in LHON asymptomatic and more frequent than in the male general population. Further, female asymptomatic LHON mutation carriers are at risk for depression and worse mental QOL scores.

Conclusions

Given the high prevalence of smoking and excessive drinking in LHON mutation carriers, implementing effective measures to reduce these risk factors may have a significant impact in reducing LHON disease conversion risk. The underrecognized prevalence of mental health issues in this population of LHON mutation carriers highlights the need for awareness and more timely diagnosis, which may lead to improved outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01724-5.

Systematic analysis of a mitochondrial disease-causing ND6 mutation in mitochondrial deficiency

Background

The m.14487T>C mutation is recognized as a diagnostic mutation of mitochondrial disease during the past 16 years, emerging evidence suggests that mutant loads of m.14487T>C and disease phenotype are not closely correlated.

Methods

Immortalized lymphocytes were generated by coculturing the Epstein–Barr virus and lymphocytes from m.14487T>C carrier Chinese patient with Leigh syndrome. Fifteen cytoplasmic hybrid (cybrid) cell lines were generated by fusing mtDNA lacking 143B cells with platelets donated by patients. Mitochondrial function was systematically analyzed at transcriptomic, metabolomic, and biochemical levels.

Results

Unlike previous reports, we found that the assembly of mitochondrial respiratory chain complexes, mitochondrial respiration, and mitochondrial OXPHOS function was barely affected in cybrid cells carrying homoplastic m.14487T>C mutation. Mitochondrial dysfunction associated transcriptomic and metabolomic reprogramming were not detected in cybrid carrying homoplastic m.14487T>C. However, we found that mitochondrial function was impaired in patient‐derived immortalized lymphocytes.

Conclusion

Our data revealed that m.14487T>C mutation is insufficient to cause mitochondrial deficiency; additional modifier genes may be involved in m.14487T>C‐associated mitochondrial disease. Our results further demonstrated that a caution should be taken by solely use of m.14487T>C mutation for molecular diagnosis of mitochondrial disease.

Investigation of frequent somatic mutations of MTND5 gene in gastric cancer cell lines and tissues

The present study investigated the single nucleotide variants (SNVs) in mitochondrial DNA (mtDNA) of 13 paired gastric cancer tissue samples and seven gastric cancer cell lines using direct sequencing analysis of the MTND5 region. Results showed that nuclear mitochondrial pseudogenes (NUMTs) and mitochondrial copy number affected the detection of the SNV frequency in gastric cancer tissue and cell line samples using high-throughput sequencing technique. The heteroplasmic point mutation C12474T and G12835A happened in AGS and BGC823 cell lines, respectively. A total of seven SNVs were found in three paired gastric cancer tissue samples, including five heteroplasmic point mutations (A12406G, C12705T, T12882C, G12501A, and A12584G) and two homoplasmic point mutations (G12561A and C13590T). Gastric cancer tissue sample 16 exhibited the highest SNVs frequency with four SNVs (np 12406, np 12705, np 12882, and np 12501), whereas no SNVs or SNPs were detected in the tissue sample 4. SNP 12705 turned out to be an SNV in gastric cancer tissue sample 16. SNV 12338 detected by exome sequencing approach appeared to be an SNP in this study.

PGD for the m.14487 T>C mitochondrial DNA mutation resulted in the birth of a healthy boy

We report on the first PGD performed for the m.14487 T>C mitochondrial DNA (mtDNA) mutation in the MT-ND6 gene, associated with Leigh syndrome. The female carrier gave birth to a healthy baby boy at age 42. This case adds to the successes of PGD for mtDNA mutations.

Idebenone: A Review in Leber's Hereditary Optic Neuropathy

Idebenone (Raxone(®)), a short-chain benzoquinone, is the only disease-specific drug approved to treat visual impairment in adolescents and adults with Leber's hereditary optic neuropathy (LHON), a rare genetic mitochondrial disease that causes rapid and progressive bilateral vision loss. The mechanism of action of idebenone involves its antioxidant properties and ability to act as a mitochondrial electron carrier. Idebenone overcomes mitochondrial complex I respiratory chain deficiency in patients with LHON by transferring electrons directly to mitochondrial complex III (by-passing complex I), thereby restoring cellular energy (ATP) production and re-activating inactive-but-viable retinal ganglion cells, which ultimately prevents further vision loss and promotes vision recovery. The approval of idebenone in the treatment of LHON was based on the overall data from a randomized clinical trial, a follow-up study and real-world data. Taken together, these studies provide convincing evidence that oral idebenone 900 mg/day for 24 weeks has persistent beneficial effects in preventing further vision impairment and promoting vision recovery in patients with LHON relative to the natural course of the disease. Therefore, idebenone is a valuable agent to treat visual impairment in adolescents and adults with LHON.