Identification of a Novel Mitochondrial tRNA Mutation in Chinese Family with Type 2 Diabetes Mellitus

Abstract

Background Mutations in mitochondrial tRNA (mt-tRNA) could be the origin of some type 2 diabetes mellitus (T2DM) cases, but the mechanism remained largely unknown. Aim The aim of this study was to assess the impact of a novel mitochondrial tRNA Cys /tRNA Tyr A5826G mutation on the development and progression of T2DM. Methods A four-generation Han Chinese family with maternally inherited diabetes underwent clinical, genetic and biochemical analyses. The mitochondrial DNA (mtDNA) mutations of three matrilineal relatives were screened by PCR-Sanger sequencing. Furthermore, to see whether m.A5826G mutations affected mitochondrial functions, the cybrid cell lines were derived from three subjects with m.A5826G mutation and three controls without this mutation. ATP was evaluated by luminescent cell viability assay, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) were determined by flow cytometry. The student’s two-tailed, unpaired t -test was used to assess the statistical significance between the control and mutant results. Results The age at onset of diabetes in this pedigree varied from 40 to 63 years, with an average of 54 years. Mutational analysis of mitochondrial genomes revealed the presence of a novel m.A5826G mutation. Interestingly, the m.A5826G mutation occurred at the conjunction between tRNA Cys and tRNA Tyr , a very conserved position that was critical for tRNAs processing and functions. Using trans-mitochondrial cybrid cells, we found that mutant cells carrying the m.A5826G showed approximately 36.5% and 22.4% reductions in ATP and MMP, respectively. By contrast, mitochondrial ROS levels increased approximately 33.3%, as compared with the wild type cells. Conclusion A novel m.A5826G mutation was identified in a pedigree with T2DM, and this mutation would lead to mitochondrial dysfunction. Thus, the genetic spectrum of mitochondrial diabetes was expanded by including m.A5826G mutation in tRNA Cys /tRNA Tyr , our study provided novel insight into the molecular pathogenesis, early diagnosis, prevention and clinical treatment for mitochondrial diabetes.

Mitochondrial Diabetes May Not Be the Only Phenotypic Presentation of the m.5826A>G mtDNA Variant [Letter]

“…We read with interest the article by Li et al about a four-generation Chinese family with maternally-inherited diabetes due to the novel mtDNA variant m.5826A>G at the conjunction between tRNA(Cys) and tRNA(Tyr). 1 Cybrid cells carrying the variant m.5826A>G showed a 36% reduction in ATP production, a 22% reduction in mitochondrial membrane potential, and a 33% increase in ROS production compared to wild-type cells. 1 It was concluded that the m.5826A>G variant is pathogenic and presents as mitochondrial diabetes.…”

“… 1 Cybrid cells carrying the variant m.5826A>G showed a 36% reduction in ATP production, a 22% reduction in mitochondrial membrane potential, and a 33% increase in ROS production compared to wild-type cells. 1 It was concluded that the m.5826A>G variant is pathogenic and presents as mitochondrial diabetes. 1 The study is attractive but raises concerns that should be discussed.…”

“… 1 It was concluded that the m.5826A>G variant is pathogenic and presents as mitochondrial diabetes. 1 The study is attractive but raises concerns that should be discussed.…”

“…The first point is that the clinically affected and unaffected family members have not been studied prospectively for multisystem disease. 1 Since mitochondrial disorders (MIDs) due to mtDNA variants manifest phenotypically maximally initially in a single organ or tissue but become a multisystem disease either at the onset or during disease progression, it is imperative to prospectively screen these patients for multisystem involvement. Multisystem involvement can occur not only in the brain, eyes or kidneys due to complications of poorly controlled diabetes, but also in organs not normally affected by diabetic complications.…”

“…The second point is that according to table 1, two patients had hypoacusis. 1 Therefore, these patients should be classified as having maternally inherited diabetes and deafness (MIDD) syndrome. 2 If these two patients also have additional phenotypic features, they should even be classified as MIDD plus.…”