Mitochondrial C4375T mutation might be a molecular risk factor in a maternal Chinese hypertensive family under haplotype C

A novel pathogenic mitochondrial DNA variant m.4344T>C in tRNAGln causes developmental delay

Mitochondrial diseases are a group of genetic diseases caused by mutations in mitochondrial DNA and nuclear DNA. However, the genetic spectrum of this disease is not yet complete. In this study, we identified a novel variant m.4344T>C in mitochondrial tRNAGln from a patient with developmental delay. The mutant loads of m.4344T>C were 95% and 89% in the patient's blood and oral epithelial cells, respectively. Multialignment analysis showed high evolutionary conservation of this nucleotide. TrRosettaRNA predicted that m.4344T>C variant would introduce an additional hydrogen bond and alter the conformation of the T-loop. The transmitochondrial cybrid-based study demonstrated that m.4344T>C variant impaired the steady-state level of mitochondrial tRNAGln and decreased the contents of mitochondrial OXPHOS complexes I, III, and IV, resulting in defective mitochondrial respiration, elevated mitochondrial ROS production, reduced mitochondrial membrane potential and decreased mitochondrial ATP levels. Altogether, this is the first report in patient carrying the m.4344T>C variant. Our data uncover the pathogenesis of the m.4344T>C variant and expand the genetic mutation spectrum of mitochondrial diseases, thus contributing to the clinical diagnosis of mitochondrial tRNAGln gene variants-associated mitochondrial diseases.

Co-occurrence of m.15992A>G and m.15077G>A Is Associated With a High Penetrance of Maternally Inherited Hypertension in a Chinese Pedigree

BACKGROUND

Mitochondrial DNA (mtDNA) pathogenic variants have been identified to be associated with maternally inherited essential hypertension (MIEH). However, the distinctive clinical features and molecular pathogenesis of MIEH are not fully understood.

METHODS

In this study, we collected a Chinese MIEH family with extraordinary higher penetrance of essential hypertension (88.89%) and early ages of onset (31-40 years old), and performed clinical and genetic characterization for this family. The complete mitochondrial genome of the proband was sequenced and analyzed.

RESULTS

The maternally related members in this family were presented with severe increased blood pressure, left ventricular remodeling, and metabolic abnormalities. Through sequencing the entire mtDNA of the proband and performing systematic analysis of the mtDNA variants with a phylogenic approach, we identified a potentially pathogenic tRNA variant (m.15992A>G in the MT-TP gene) that may account for the MIEH in this family. One nonsynonymous variant (m.15077G>A in the MT-CYB gene) was identified to play a synergistic role with m.15992A>G to cause a high penetrance of MIEH.

CONCLUSIONS

Our results, together with previous findings, have indicated that tRNA pathogenic variants in the mtDNA could act important roles in the pathogenesis of MIEH through reducing mitochondrial translation and disturbing mitochondrial function.

Associations of mitochondrial DNA 3777-4679 region mutations with maternally inherited essential hypertensive subjects in China

Background

Nuclear genome or family mitochondrial screening system has become the hot focus of studies into essential hypertension. The role of mitochondrial DNA (mtDNA) in sporadic Chinese patients with hypertension has not been fully understood. The study was to evaluate the associations of mtDNA mutations with maternally inherited essential hypertensive subjects in China.

Methods

From June 2009 to June 2016, a total of 800 gender-matched Chinese patients with maternally inherited essential hypertension (MIEH) and control group were 1:1 enrolled in this case-control study. Genomic DNA was extracted from each person’s peripheral blood cells. The main mtDNA locations for MIEH were screened with oligodeoxynucleotides 3777-4679 bp, analyzed and compared with the updated consensus Cambridge Sequence. Pathogenic mtDNA mutations were identified from the mitochondrial map.

Results

MIEH subjects presented significantly higher values than those of control group in abdominal circumference (AC), waist circumference (WC), body mass index (BMI), fasting blood glucose (FBG), triglyceride (TG), low-density lipoprotein cholesterol (LDL) and renal function (P < 0.05). MIEH subjects carried more amino acid changes and coding sequence variants (P < 0.01) than control group. The allele frequencies of the eight single nucleotide polymorphisms (SNPs) were significantly different between the two groups, including m.3970 C > T, m.4048G > A, m.4071C > T, m.4086C > T, m. 4164A > G and m.4248 T > C in ND1 gene, and m.4386 T > C and m.4394C > T in tRNA^Gln gene(P < 0.001). Fifty-five homoplasmic or heteroplasmic mutations were detected in 5 genes: ND1, tRNA^Ile, tRNA^Met, tRNA^Gln and ND2 gene. The ND1 gene was the main mutation site, where the most mtDNA mutation was m.3970 C > T.

Conclusions

The mtDNA mutations were involved in the process of MIEH. We identified mitochondrial genetic characteristics in MIEH patients in China. The present research serves as a solid foundation for further detailed research on the association between MIEH and mitochondrial dysfunction, and their causal relationship in Chinese and other populations with a similar lifestyle.

The mitochondrial tRNAAla 5587T>C and tRNALeu(CUN) 12280A>G mutations may be associated with hypertension in a Chinese family

Hypertension is a very common cardiovascular disorder, however, the molecular mechanism underlying this disease remains poorly understood. Recently, an increasing number of studies have demonstrated that mitochondrial (mt)DNA mutations serve important roles in the pathogenesis of hypertension. The current study reported the clinical and molecular characterization of a Chinese family with maternally inherited hypertension (the penetrance of hypertension was 71.4%). In addition, the entire mitochondrial transfer (mt-t)RNA genomes was amplified using a polymerase chain reaction (PCR) and identified through direct Sanger sequencing. Additionally, the mtDNA copy number in matrilineal relatives in this family was evaluated using quantitative PCR. The sequence analysis of the 22 mt-tRNA genes led to the identification of tRNA^Ala 5587T>C (thymine to cytosine) and tRNA^Leu(CUN) 12280A>G (adenine to guanine) mutations. Notably, the heteroplasmic 5587T>C mutation was located at the 3' end of tRNA^Ala (position 73), which is highly conserved from bacteria to human mitochondria. In addition, the 12280A>G mutation was revealed to occurs at the dihydrouridine loop of tRNA^Leu(CUN) (position 15) and may decrease the steady-state level of mt-tRNA. As a result, 5587T>C and 12280A>G mutations may lead to the failure of tRNAs metabolism and subsequently cause mitochondrial protein synthesis defects. Molecular analysis revealed that patients carrying the 5587T>C and 12280A>G mutations had a lower copy number of mtDNA compared with a control with hypertension, but without the mutations, suggesting that these mutations may cause mitochondrial dysfunctions that are responsible for hypertension. Therefore, mt-tRNA^Ala 5587T>C and tRNA^Leu(CUN) 12280A>G mutations may be involved in the pathogenesis of hypertension in this family.