The m.3890G>A/MT-ND1 mtDNA rare pathogenic variant: Expanding clinical and MRI phenotypes

Leber's hereditary optic neuropathy like disease in MT-ATP6 variant m.8969G>A

Purpose

To describe a case with Leber's hereditary optic neuropathy (LHON) like optic atrophy in the presence of MT-ATP6 gene variant m.8969G > A.

Observations

A 20-year-old patient with a history of mild developmental delay, mild cognitive impairment, and positional tremor presented with subacute painless visual loss over a few weeks. Mitochondrial genome sequencing revealed a variant in MT-ATP6, m.8969G > A (p.Ser148Asn). This variant was previously reported in association with mitochondrial myopathy, lactic acidosis, and sideroblastic anemia (MLASA) and with nephropathy, followed by brain atrophy, muscle weakness and arrhythmias, but not with optic atrophy.

Conclusions and importance

Rare variants in MT-ATP6 can also cause LHON like optic atrophy. It is important to perform further genetic analysis of mitochondrial DNA in genetically unsolved cases suspected of Leber's hereditary optic neuropathy to confirm the clinical diagnosis.

Mitochondrial complex I subunit MT-ND1 mutations affect disease progression

Mitochondrial respiratory chain complex I is an important component of the oxidative respiratory chain, with the mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1 (MT-ND1) being one of the core subunits. MT-ND1 plays a role in the assembly of complex I and its enzymatic function. MT-ND1 gene mutation affects pathophysiological processes, such as interfering with the early assembly of complex I, affecting the ubiquinone binding domain and proton channel of complex I, and affecting oxidative phosphorylation, thus leading to the occurrence of diseases. The relationship between MT-ND1 gene mutation and disease has been has received increasing research attention. Therefore, this article reviews the impact of MT-ND1 mutations on disease progression, focusing on the impact of such mutations on diseases and their possible mechanisms, as well as the application of targeting MT-ND1 gene mutations in disease diagnosis and treatment. We aim to provide a new perspective leading to a more comprehensive understanding of the relationship between MT-ND1 gene mutations and diseases.

Engineering RsDddA as mitochondrial base editor with wide target compatibility and enhanced activity

Double-stranded DNA-specific cytidine deaminase (DddA) base editors hold great promise for applications in bio-medical research, medicine, and biotechnology. Strict sequence preference on spacing region presents a challenge for DddA editors to reach their full potential. To overcome this sequence-context constraint, we analyzed a protein dataset and identified a novel DddAtox homolog from Ruminococcus sp. AF17-6 (RsDddA). We engineered RsDddA for mitochondrial base editing in a mammalian cell line and demonstrated RsDddA-derived cytosine base editors (RsDdCBE) offered a broadened NC sequence compatibility and exhibited robust editing efficiency. Moreover, our results suggest the average frequencies of mitochondrial genome-wide off-target editing arising from RsDdCBE are comparable to canonical DdCBE and its variants.

Novel biallelic mutations in TMEM126B cause splicing defects and lead to Leigh-like syndrome with severe complex I deficiency

Leigh syndrome (LS)/Leigh-like syndrome (LLS) is one of the most common mitochondrial disease subtypes, caused by mutations in either the nuclear or mitochondrial genomes. Here, we identified a novel intronic mutation (c.82-2 A > G) and a novel exonic insertion mutation (c.290dupT) in TMEM126B from a Chinese patient with clinical manifestations of LLS. In silico predictions, minigene splicing assays and patients’ RNA analyses determined that the c.82-2 A > G mutation resulted in complete exon 2 skipping, and the c.290dupT mutation provoked partial and complete exon 3 skipping, leading to translational frameshifts and premature termination. Functional analysis revealed the impaired mitochondrial function in patient-derived lymphocytes due to severe complex I content and assembly defect. Altogether, this is the first report of LLS in a patient carrying mutations in TMEM126B. Our data uncovers the functional effect and the molecular mechanism of the pathogenic variants c.82-2 A > G and c.290dupT, which expands the gene mutation spectrum of LLS and clinical spectrum caused by TMEM126B mutations, and thus help to clinical diagnosis of TMEM126B mutation‐related mitochondrial diseases.

Mitochondrial respiratory complexes: Significance in human mitochondrial disorders and cancers

Mitochondria are pivotal organelles that govern cellular energy production through the oxidative phosphorylation system utilizing five respiratory complexes. In addition, mitochondria also contribute to various critical signaling pathways including apoptosis, damage-associated molecular patterns, calcium homeostasis, lipid, and amino acid biosynthesis. Among these diverse functions, the energy generation program oversee by mitochondria represents an immaculate orchestration and functional coordination between the mitochondria and nuclear encoded molecules. Perturbation in this program through respiratory complexes' alteration results in the manifestation of various mitochondrial disorders and malignancy, which is alarmingly becoming evident in the recent literature. Considering the clinical relevance and importance of this emerging medical problem, this review sheds light on the timing and nature of molecular alterations in various respiratory complexes and their functional consequences observed in various mitochondrial disorders and human cancers. Finally, we discussed how this wealth of information could be exploited and tailored to develop respiratory complex targeted personalized therapeutics and biomarkers for better management of various incurable human mitochondrial disorders and cancers.