Prevalence and clinical characterization of Japanese diabetes mellitus with an A-to-G mutation at nucleotide 3243 of the mitochondrial tRNA(Leu(UUR)) gene

Pathogenic mitochondrial DNA 3243A>G mutation: From genetics to phenotype

The mitochondrial DNA (mtDNA) m.3243A>G mutation is one of the most common pathogenic mtDNA variants, showing complex genetics, pathogenic molecular mechanisms, and phenotypes. In recent years, the prevention of mtDNA-related diseases has trended toward precision medicine strategies, such as preimplantation genetic diagnosis (PGD) and mitochondrial replacement therapy (MRT). These techniques are set to allow the birth of healthy children, but clinical implementation relies on thorough insights into mtDNA genetics. The genotype and phenotype of m.3243A>G vary greatly from mother to offspring, which compromises genetic counseling for the disease. This review is the first to systematically elaborate on the characteristics of the m.3243A>G mutation, from genetics to phenotype and the relationship between them, as well as the related influencing factors and potential strategies for preventing disease. These perceptions will provide clarity for clinicians providing genetic counseling to m.3243A>G patients.

A Deafness- and Diabetes-associated tRNA Mutation Causes Deficient Pseudouridinylation at Position 55 in tRNAGlu and Mitochondrial Dysfunction

Several mitochondrial tRNA mutations have been associated with maternally inherited diabetes and deafness. However, the pathophysiology of these tRNA mutations remains poorly understood. In this report, we identified the novel homoplasmic 14692A→G mutation in the mitochondrial tRNA^Glu gene among three Han Chinese families with maternally inherited diabetes and deafness. The m.14692A→G mutation affected a highly conserved uridine at position 55 of the TΨC loop of tRNA^Glu The uridine is modified to pseudouridine (Ψ55), which plays an important role in the structure and function of this tRNA. Using lymphoblastoid cell lines derived from a Chinese family, we demonstrated that the m.14692A→G mutation caused loss of Ψ55 modification and increased angiogenin-mediated endonucleolytic cleavage in mutant tRNA^Glu The destabilization of base-pairing (18A-Ψ55) caused by the m.14692A→G mutation perturbed the conformation and stability of tRNA^Glu An approximately 65% decrease in the steady-state level of tRNA^Glu was observed in mutant cells compared with control cells. A failure in tRNA^Glu metabolism impaired mitochondrial translation, especially for polypeptides with a high proportion of glutamic acid codons such as ND1, ND6, and CO2 in mutant cells. An impairment of mitochondrial translation caused defective respiratory capacity, especially reducing the activities of complexes I and IV. Furthermore, marked decreases in the levels of mitochondrial ATP and membrane potential were observed in mutant cells. These mitochondrial dysfunctions caused an increasing production of reactive oxygen species in the mutant cells. Our findings may provide new insights into the pathophysiology of maternally inherited diabetes and deafness, which is primarily manifested by the deficient nucleotide modification of mitochondrial tRNA^Glu.

Treatment of Mitochondrial Diabetes with a Peroxisome Proliferator-activated Receptor (PPAR)-gamma Agonist

The 3243 A>G mutation in mitochondrial DNA is the most common cause of monogenic diabetes mellitus in Japan. A 45-year-old woman with mitochondrial diabetes and significant insulin resistance presented with hypoadiponectinemia despite a normal amount of visceral fat. Three months of treatment with pioglitazone (PIO) improved her blood glucose profile and response to the 75-g oral glucose tolerance test. These changes were accompanied by the amelioration of her insulin resistance and the impairment of early-phase insulin secretion. Her serum adiponectin levels increased to the normal range. In this case of mitochondrial diabetes, PIO was effective for glycemic control.

Endocrine disorders in mitochondrial disease

Endocrine dysfunction in mitochondrial disease is commonplace, but predominantly restricted to disease of the endocrine pancreas resulting in diabetes mellitus. Other endocrine manifestations occur, but are relatively rare by comparison. In mitochondrial disease, neuromuscular symptoms often dominate the clinical phenotype, but it is of paramount importance to appreciate the multi-system nature of the disease, of which endocrine dysfunction may be a part. The numerous phenotypes attributable to pathogenic mutations in both the mitochondrial (mtDNA) and nuclear DNA creates a complex and heterogeneous catalogue of disease which can be difficult to navigate for novices and experts alike. In this article we provide an overview of the endocrine disorders associated with mitochondrial disease, the way in which the underlying mitochondrial disorder influences the clinical presentation, and how these factors influence subsequent management.

Pathogenic mitochondrial DNA mutations are common in the general population

Mitochondrial DNA (mtDNA) mutations are a major cause of genetic disease, but their prevalence in the general population is not known. We determined the frequency of ten mitochondrial point mutations in 3168 neonatal-cord-blood samples from sequential live births, analyzing matched maternal-blood samples to estimate the de novo mutation rate. mtDNA mutations were detected in 15 offspring (0.54%, 95% CI = 0.30–0.89%). Of these live births, 0.00107% (95% CI = 0.00087–0.0127) harbored a mutation not detected in the mother's blood, providing an estimate of the de novo mutation rate. The most common mutation was m.3243A→G. m.14484T→C was only found on sub-branches of mtDNA haplogroup J. In conclusion, at least one in 200 healthy humans harbors a pathogenic mtDNA mutation that potentially causes disease in the offspring of female carriers. The exclusive detection of m.14484T→C on haplogroup J implicates the background mtDNA haplotype in mutagenesis. These findings emphasize the importance of developing new approaches to prevent transmission.

Cardiac autonomic nervous dysfunction in diabetic patients with a mitochondrial DNA mutation: assessment by heart rate variability

OBJECTIVE

To elucidate the degree and characteristics of cardiac autonomic nervous dysfunction in diabetic patients associated with a mitochondrial DNA mutation at base pair 3243.

RESEARCH DESIGN AND METHODS

We investigated heart rate variability using 24-h Holter monitoring in 10 diabetic patients with the mutation compared with 55 ordinary diabetic patients and 45 nondiabetic control subjects.

RESULTS

Age and sex were similar in the three groups. Between patients with the mutation and ordinary diabetic patients, the duration of diabetes and blood glycemic levels were not different. In the time domain analysis of heart rate variability, patients with the mutation and ordinary diabetic patients had significantly smaller SDNN index and pNN50 than control subjects. Compared with ordinary diabetic patients, patients with the mutation had smaller SDNN index (P < 0.02), but rMSSD and pNN50 were not different. In the frequency domain analysis, total, low frequency (LF), and high frequency (HF) spectra were significantly smaller in patients with the mutation and ordinary diabetic patients than in control subjects. Compared with ordinary diabetic patients, patients with the mutation had smaller total and LF spectra (P < 0.02). However, HF spectra were not significantly different. Notably, the LF/HF spectra ratio was lower in patients with the mutation than in ordinary diabetic patients and control subjects (P < 0.05), but this ratio was similar in ordinary diabetic patients and control subjects.

CONCLUSIONS

Our results suggest that diabetic patients with the mitochondrial DNA mutation have more severely impaired cardiac autonomic nervous function with sympathovagal imbalance, as compared with ordinary diabetic patients.

Diminished insulin secretory response to glucose but normal insulin and glucagon secretory responses to arginine in a family with maternally inherited diabetes and deafness caused by mitochondrial tRNA(LEU(UUR)) gene mutation

OBJECTIVE

The effects of glucose, arginine, and glucagon on beta-cell function as well as alpha-cell response to arginine were studied in a family with mitochondrial diabetes.

RESEARCH DESIGN AND METHODS

The function of alpha- and beta-cells was assessed in all five siblings carrying the mitochondrial tRNA Leu(UUR) gene mutation at position 3243 and compared with six sex-, age-, and weight-matched control subjects. Insulin and C-peptide responses were evaluated by intravenous glucagon application, intravenous arginine stimulation test, and intravenous glucose tolerance test. Glucagon secretion was assessed during the arginine stimulation test.

RESULTS

The glucose disappearance constant (K(g)) value (mean +/- SEM 0.61 +/- 0.04 vs. 1.1 +/- 0.04, P = 0.0002) as well as the acute insulin response to glucose (area under the curve [AUC] 0-10 min, 77.7 +/- 50.7 vs. 1,352.3 +/- 191.5 pmol/l, P = 0.0004) were decreased in all patients. Similarly, glucagon-stimulated C-peptide response was also impaired (728 +/- 111.4 vs. 1,526.7 +/- 157.7 pmol/l, P = 0.005), whereas the insulin response to arginine (AUC) was normal (1,346.9 +/- 710.8 vs. 1,083.2 +/- 132.5 pmol/l, P = 0.699). Acute glucagon response to arginine (AUC) was normal but tended to be higher in the patients than in the control subjects (181.7 +/- 47.5 vs. 90.0 +/- 21.1 pmol/l, P = 0.099).

CONCLUSIONS

This study shows impaired insulin and C-peptide secretion in response to a glucose challenge and to glucagon stimulation in diabetic patients with mitochondrial tRNA Leu(UUR) gene mutation, although insulin and glucagon secretory responses to arginine were normal.

Prevalence of Japanese dialysis patients with an A-to-G mutation at nucleotide 3243 of the mitochondrial tRNA(Leu(UUR)) gene

BACKGROUND

A high prevalence of an A-to-G mutation at nucleotide 3243 of the mitochondrial genome in patients with diabetes mellitus (DM) and/or deafness has been reported previously. We investigated the prevalence of this mutation in Japanese dialysis patients with associated DM and/or deafness.

METHODS

We studied 106 dialysis patients with DM, 26 with DM and deafness, and 26 with deafness alone, using peripheral leucocytes to detect an A-to-G transition at nucleotide 3243 of the mitochondrial gene.

RESULTS

We identified this transition in 1 of 26 patients with DM and deafness. None of the 106 DM or 26 dialysis patients with deafness but no DM was positive for this mutation. A 42-year-old male patient on continuous ambulatory peritoneal dialysis (CAPD) who carried this mutation had a 20-year history of sensory hearing loss as well as hypertrophic cardiomyopathy.

CONCLUSION

We found that a mitochondrial gene mutation at nucleotide 3243 was present in one dialysis patient with NIDDM and deafness. The prevalence of this mutation was found to be below 1% in diabetic end-stage renal disease patients in Japan.