Mitochondrial diabetes mellitus: a review

Mitochondrial Diabetes Mellitus With Mitochondrial DNA 3316G>A Mutation: A Unique Autopsy Case Presenting With Sepsis-Associated Cholestasis

A 70-year-old female, diagnosed with mitochondrial diabetes mellitus (MDM) showing previously a point mutation at mitochondrial DNA 3316G>A, noticed urinary tract infection and diabetic gangrene of the foot with Gram-negative Bacteroides fragilis bacteremia, followed by aggressive jaundice with high serum level of direct bilirubin. She died two months after the symptom onset. At autopsy, multiple foci of bacteremia-induced hemorrhagic infarction were observed in the congestive bilateral lungs, whereas the cholestatic liver revealed no overt gross cholangiectasis. Microscopic findings characteristically showed many bile thrombi in the biliary canaliculi of hepatic lobules without any evidence of severe shock liver. Finally, we diagnosed it exclusively as sepsis-associated cholestasis due to the marked elevation of Gram-negative bacteria-derived endotoxins and inflammatory cytokines. We propose that these unique liver features in our MDM case might be one of the new clues to unveil its enigmatic etiology.

Mitochondrial DNA abnormalities and metabolic syndrome

Metabolic syndrome (MetS) is a complex pathological condition that involves disrupted carbohydrate, protein, and fat metabolism in the human body, and is a major risk factor for several chronic diseases, including diabetes, cardiovascular disease, and cerebrovascular disease. While the exact pathogenesis of metabolic syndrome is not yet fully understood, there is increasing evidence linking mitochondrial dysfunction, which is closely related to the mitochondrial genome and mitochondrial dynamics, to the development of this condition. Recent advancements in genetic sequencing technologies have allowed for more accurate detection of mtDNA mutations and other mitochondrial abnormalities, leading to earlier diagnosis and intervention in patients with metabolic syndrome. Additionally, the identification of specific mechanisms by which reduced mtDNA copy number and gene mutations, as well as abnormalities in mtDNA-encoded proteins and mitochondrial dynamics, contribute to metabolic syndrome may promote the development of novel therapeutic targets and interventions, such as the restoration of mitochondrial function through the targeting of specific mitochondrial defects. Additionally, advancements in genetic sequencing technologies may allow for more accurate detection of mtDNA mutations and other mitochondrial abnormalities, leading to earlier diagnosis and intervention in patients with MetS. Therefore, strategies to promote the restoration of mitochondrial function by addressing these defects may offer new options for treating MetS. This review provides an overview of the research progress and significance of mitochondrial genome and mitochondrial dynamics in MetS.

Insulin Resistance in Mitochondrial Diabetes

Mitochondrial diabetes (MD) is generally classified as a genetic defect of β-cells. The main pathophysiology is insulin secretion failure in pancreatic β-cells due to impaired mitochondrial ATP production. However, several reports have mentioned the presence of insulin resistance (IR) as a clinical feature of MD. As mitochondrial dysfunction is one of the important factors causing IR, we need to focus on IR as another pathophysiology of MD. In this special issue, we first briefly summarized the insulin signaling and molecular mechanisms of IR. Second, we overviewed currently confirmed pathogenic mitochondrial DNA (mtDNA) mutations from the MITOMAP database. The variants causing diabetes were mostly point mutations in the transfer RNA (tRNA) of the mitochondrial genome. Third, we focused on these variants leading to the recently described "tRNA modopathies" and reviewed the clinical features of patients with diabetes. Finally, we discussed the pathophysiology of MD caused by mtDNA mutations and explored the possible mechanism underlying the development of IR. This review should be beneficial to all clinicians involved in diagnostics and therapeutics related to diabetes and mitochondrial diseases.

Is Type 2 Diabetes a Primary Mitochondrial Disorder?

Diabetes mellitus is the most common endocrine disturbance in inherited mitochondrial diseases. It is essential to increase awareness of the correct diagnosis and treatment of diabetes in these patients and screen for the condition in family members, as diabetes might appear with distinctive clinical features, complications and at different ages of onset. The severity of mitochondrial-related diabetes is likely to manifest on a large scale of phenotypes depending on the location of the mutation and whether the number of affected mitochondria copies (heteroplasmy) reaches a critical threshold. Regarding diabetes treatment, the first-choice treatment for type 2 diabetes (T2D), metformin, is not recommended because of the risk of lactic acidosis. The preferred treatment for diabetes in patients with mitochondrial disorders is SGLT-2i and mitochondrial GLP-1-related substances. The tight relationship between mitochondrial dysfunction, reduced glucose-stimulated insulin secretion (GSIS), and diabetes development in human patients is acknowledged. However, despite the well-characterized role of mitochondria in GSIS, there is a relative lack of data in humans implicating mitochondrial dysfunction as a primary defect in T2D. Our recent studies have provided data supporting the significant role of the mitochondrial respiratory-chain enzyme, cytochrome c oxidase (COX), in regulating GSIS in a rodent model of T2D, the Cohen diabetic sensitive (CDs) rat. The nutritionally induced diabetic CDs rat demonstrates several features of mitochondrial diseases: markedly reduced COX activity in several tissues, increased reactive oxygen production, decreased ATP generation, and increased lactate dehydrogenase expression in islets. Moreover, our data demonstrate that reduced islet-COX activity precedes the onset of diabetes, suggesting that islet-COX deficiency is the primary defect causing diabetes in this model. This review examines the possibility of including T2D as a primary mitochondrial-related disease. Understanding the critical interdependence between diabetes and mitochondrial dysfunction, centering on the role of COX, may open novel avenues to diagnose and treat diabetes in patients with mitochondrial diseases and mitochondrial dysfunction in diabetic patients.

Cytochrome c Oxidase Activity as a Metabolic Regulator in Pancreatic Beta-Cells

Pancreatic β-cells couple glucose-stimulated insulin secretion (GSIS) with oxidative phosphorylation via cytochrome c oxidase (COX), a mitochondrial respiratory-chain enzyme. The Cohen diabetic-sensitive (CDs) rats exhibit hyperglycemia when fed a diabetogenic diet but maintain normoglycemia on a regular diet. We have previously reported a decreased COX activity in CDs rats and explored its relevance for type 2 diabetes (T2D). In this study, we investigated the relation between COX activity in islets, peripheral-blood mononuclear cells (PBMCs), and GSIS during diabetes development in CDs rats fed a diabetogenic diet for 4, 11, 20, and 30 days and during reversion to normoglycemia in hyperglycemic CDs rats fed a reversion diet for 7, 11, and 20 days. An oral glucose-tolerance test was performed at different periods of the diets measuring blood glucose and insulin concentrations. COX activity was determined in islets and PBMCs isolated from rats at the different periods of the diets. We demonstrated a progressive reduction in COX activity in CDs-islets that correlated positively with the decreasing GSIS (R2 = 0.9691, p < 0.001) and inversely with the elevation in blood glucose levels (R2 = 0.8396, p < 0.001). Hyperglycemia was initiated when islet COX activity decreased below 46%. The reversion diet restored >46% of the islet COX activity and GSIS while re-establishing normoglycemia. Interestingly, COX activity in PBMCs correlated significantly with islet COX activity (R2 = 0.8944, p < 0.001). Our data support islet COX activity as a major metabolic regulator of β-cells function. The correlation between COX activity in PBMCs and islets may serve as a noninvasive biomarker to monitor β-cell dysfunction in diabetes.

Neurological manifestations in m.3243A>G-related disease triggered by metformin

INTRODUCTION

m.3243A>G-related disease has multi-systemic manifestations including diabetes mellitus. It is uncertain whether metformin would trigger neurological manifestations of this disease. This study aims to review the diagnosis and management of m.3243A>G-related diabetes genetically confirmed by our laboratory and to evaluate the risk of metformin use triggering neurological manifestations.

METHODS

Cases with m.3243A>G detected between 2009 and 2020 were reviewed. Cases with diabetes mellitus were included. Cases with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) before diabetes onset were excluded. Odds ratio was calculated for association between metformin use and newly developed neurological manifestations.

RESULTS

Sixteen patients were identified. Odds ratio for metformin use was 3.50 [0.37-33.0; p = 0.3287]. One illustrative case with clear causal relationship between metformin use and neurological manifestations was described in detail.

CONCLUSION

m.3243A>G-related diabetes mellitus is underdiagnosed. Red flags including positive family history, short stature, low body weight and hearing loss are often overlooked. Early diagnosis allows regular systemic assessment. In the era of precision medicine and novel therapies, it is prudent to avoid metformin as it could trigger neurological manifestations in this condition. Coenzyme Q10, DPP-IV inhibitors, SGLT2 inhibitors and GLP-1 receptor agonists may be considered.

Diabetes mellitus and hearing loss: A review

Diabetes (type 2) and sensorineural hearing loss are common health problems manifested with ageing. While both type 1 and type 2 diabetes have been associated with hearing loss, a causal link has been difficult to establish. Individuals with diabetes have twice the incidence of hearing loss compared to those without diabetes and those with prediabetes have a 30% higher rate of hearing loss. Whether hearing loss is associated with diabetes independent of glycemic control remains to be determined. Hearing loss has its own set of risk factors and shares others with diabetes. This review will summarize the complex relationship between diabetes and sensorineural hearing loss.

Clinical phenotype of mitochondrial diabetes due to rare mitochondrial DNA mutations

OBJECTIVE

While the most frequent mutation responsible for mitochondrial diabetes is the point mutation m.3243 A>G of mitochondrial DNA (mtDNA), few data are available about the role of rare mtDNA mutations in the pathophysiology of diabetes. The main objective of our study was to describe the phenotypic characteristics of patients suffering from diabetes linked to rare mtDNA mutations.

RESEARCH DESIGN AND METHODS

We performed a post-hoc analysis of a prospective multicenter cohort of 743 patients with mitochondrial disorder (previously published by the French Network of Mitochondrial Diseases), associated to a literature review of the PubMed database from 1992 to May 2016. We extracted all reported patients with diabetes and identified rare mtDNA mutations and described their clinical and metabolic phenotypes.

RESULTS

The 50 identified patients (10 from the princeps study; 40 from the review of the literature) showed a heterogeneous metabolic phenotype in terms of age, symptoms prior to diagnosis, treatments, and associated clinical and biological signs. However, neurological symptoms were more frequent in case of rare mtDNA mutations compared to the classical m.3243 A>G mutation (P=0.024). In contrast, deafness (65% vs. 95%, P=3.7E-5), macular pattern dystrophy (20% vs. 86%, P=1.6E-10) and nephropathy (8% vs. 28%, P=0.018) were significantly less frequent than in case of the classical m.3243 A>G mutation.

CONCLUSION

Although no specific metabolic phenotype could be identified suggesting or eliminating implication of rare mtDNA mutations in diabetes, clinical phenotypes featured more frequent neurological signs.

Melatonin, mitochondria and hypertension

Melatonin, due to its multiple means and mechanisms of action, plays a fundamental role in the regulation of the organismal physiology by fine tunning several functions. The cardiovascular system is an important site of action as melatonin regulates blood pressure both by central and peripheral interventions, in addition to its relation with the renin-angiotensin system. Besides, the systemic management of several processes, melatonin acts on mitochondria regulation to maintain a healthy cardiovascular system. Hypertension affects target organs in different ways and cellular energy metabolism is frequently involved due to mitochondrial alterations that include a rise in reactive oxygen species production and an ATP synthesis decrease. The discussion that follows shows the role played by melatonin in the regulation of mitochondrial physiology in several levels of the cardiovascular system, including brain, heart, kidney, blood vessels and, particularly, regulating the renin-angiotensin system. This discussion shows the putative importance of using melatonin as a therapeutic tool involving its antioxidant potential and its action on mitochondrial physiology in the cardiovascular system.

Combined Application of UHPLC-QTOF/MS, HPLC-ELSD and 1 H-NMR Spectroscopy for Quality Assessment of DA-9801, A Standardised Dioscorea Extract

INTRODUCTION

DA-9801, a standardised 50% aqueous ethanolic extract of a mixture of Dioscorea japonica and D. nipponica, is a botanical drug candidate for the treatment of diabetic neuropathy, which finished its US phase II clinical trials recently. An advanced quality control method is needed for further development of DA-9801, considering its high contents of both primary and secondary metabolites.

OBJECTIVE

Development of a quality assessment strategy for DA-9801, based on the combination of UHPLC-QTOF/MS, HPLC-ELSD, and ¹ H-NMR spectroscopy.

METHODS

The method was developed and tested with 15 batch products of DA-9801. The steroidal saponins of DA-9801 were tentatively identified by UHPLC-QTOF/MS and were quantified with the validated HPLC-ELSD method. Primary metabolites of DA-9801 were identified and profiled using ¹ H-NMR spectrometry. The batch-to-batch equivalence of DA-9801 was tested with the ¹ H-NMR spectra using spectral binning, correlation analysis, and principal component analysis.

RESULTS

Six major saponins of DA-9801 were tentatively identified by UHPLC-QTOF/MS. Among them, protodioscin and dioscin were quantified by the validated HPLC-ELSD method. Twenty-six metabolites were identified in ¹ H-NMR spectra. The similarity between DA-9801 batches could be evaluated with the NMR spectra of DA-9801. The ¹ H-NMR method also revealed that two Dioscorea species contributed distinct amino acids to the contents of DA-9801.

CONCLUSION

This study validates the effectiveness of UHPLC-QTOF/MS, HPLC-ELSD, and ¹ H NMR-combined method for quality control of DA-9801 and its crude materials. Copyright © 2016 John Wiley & Sons, Ltd.

Low prevalence of patients with mitochondrial disease in the German/Austrian DPV diabetes registry

The aim of this study was to characterize the phenotype and treatment of young patients (manifestation <30 years) with diabetes of mitochondrial origin (DMO), based on the German/Austrian DPV (Diabetes Patienten Verlaufsdokumentation) registry. Only 13 (0.02 %) of all patients with diabetes in this cohort were identified with DMO, mainly due to the Kearns-Sayre (n = 5), Pearson (n = 3), or mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome (n = 2). The onset of DMO (14.2, interquartile range (IQR) 7.1-16 years) was later than diabetes onset in individuals with T1D but earlier than in T2D. At manifestation, patients exhibited a mild elevation of blood glucose concentrations (251, IQR 178-299 mg/dl) without ketoacidosis. They had lower body mass index (BMI) values (-1.39 ± 0.28 kg/m(2)) than peers with T1D or T2D (p < 0.0001) and higher triglycerides (211, IQR 134-574 mg/dl) than in T1D (p = 0.04) while there was a high rate of dyslipidemia (86 %). Insulin requirements (0.58, IQR 0.37-0.90 U/kg/d) were between T1D and T2D while glucometabolic control (glycated hemoglobin A1c (HbA1c) 7.4 ± 0.52 %) in DMO was comparable to age-matched T2D and stable over a 5-year follow-up.

CONCLUSION

Primary mitochondrial disorders are a rare cause of juvenile diabetes and likely to be underdiagnosed. As there is clinical overlap with T1D and T2D, dyslipidemia and low body weight may help to identify further DMO cases.

WHAT IS KNOWN

• In adults diabetes of mitochondrial origin (DMO) is a rare cause of non-autoimmune diabetes, affecting about 0.8 % of diabetes cases. • Common features are a maternal family history of diabetes, hearing loss and neurological abnormalities. What is New: • In our juvenile cohort 0.02 % of diabetes patients (age < 30 years) were affected by DMO, while Kearns Sayre, MELAS and Pearson syndrome were the most frequent entities. • Juvenile DMO patients exhibited dyslipidemia, higher triglycerides and a lower BMI than peers with T1D or T2D, while some patients also showed retinal changes.

The tRNA(Gly) T10003C mutation in mitochondrial haplogroup M11b in a Chinese family with diabetes decreases the steady-state level of tRNA(Gly), increases aberrant reactive oxygen species production, and reduces mitochondrial membrane potential

Mitochondrial diabetes originates mainly from mutations located in maternally transmitted, mitochondrial tRNA-coding genes. In a genetic screening program of type 2 diabetes conducted with a Chinese Han population, we found one family with suggestive maternally transmitted diabetes. The proband's mitochondrial genome was analyzed using DNA sequencing. Total 42 known nucleoside changes and 1 novel variant were identified, and the entire mitochondrial DNA sequence was assigned to haplogroup M11b. Phylogenetic analysis showed that a homoplasmic mutation, 10003T>C transition, occurred at the highly conserved site in the gene encoding tRNA(Gly). Using a transmitochondrial cybrid cell line harboring this mutation, we observed that the steady-state level of tRNA(Gly) significantly affected and the amount of tRNA(Gly) decreased by 97%, production of reactive oxygen species was enhanced, and mitochondrial membrane potential, mtDNA copy number and cellular oxygen consumption rate were remarkably decreased compared with wild-type cybrid cells. The homoplasmic 10003T>C mutation in the mitochondrial tRNA(Gly) gene suggested to be as a pathogenesis-related mutation which might contribute to the maternal inherited diabetes in the Han Chinese family.

Mitophagy and mitochondrial dynamics in Saccharomyces cerevisiae

Mitochondria fulfill central cellular functions including energy metabolism, iron-sulfur biogenesis, and regulation of apoptosis and calcium homeostasis. Accumulation of dysfunctional mitochondria is observed in ageing and many human diseases such as cancer and various neurodegenerative disorders. Appropriate quality control of mitochondria is important for cell survival in most eukaryotic cells. One important pathway in this respect is mitophagy, a selective form of autophagy which removes excess and dysfunctional mitochondria. In the past decades a series of essential factors for mitophagy have been identified and characterized. However, little is known about the molecular mechanisms regulating mitophagy. The role of mitochondrial dynamics in mitophagy is controversially discussed. Here we will review recent advances in this context promoting our understanding on the molecular regulation of mitophagy in Saccharomyces cerevisiae and on the role of mitochondrial dynamics in mitochondrial quality control.

Dioscorea Extract (DA-9801) Modulates Markers of Peripheral Neuropathy in Type 2 Diabetic db/db Mice

The purpose of this study was to investigate the therapeutic effects of DA-9801, an optimized extract of Dioscorea species, on diabetic peripheral neuropathy in a type 2 diabetic animal model. In this study, db/db mice were treated with DA-9801 (30 and 100 mg/kg, daily, p.o.) for 12 weeks. DA-9801 reduced the blood glucose levels and increased the withdrawal latencies in hot plate tests. Moreover, it prevented nerve damage based on increased nerve conduction velocity and ultrastructural changes. Decrease of nerve growth factor (NGF) may have a detrimental effect on diabetic neuropathy. We previously reported NGF regulatory properties of the Dioscorea genus. In this study, DA-9801 induced NGF production in rat primary astrocytes. In addition, it increased NGF levels in the sciatic nerve and the plasma of type 2 diabetic animals. DA-9801 also increased neurite outgrowth and mRNA expression of Tieg1/Klf10, an NGF target gene, in PC12 cells. These results demonstrated the attenuation of diabetic peripheral neuropathy by oral treatment with DA-9801 via NGF regulation. DA-9801 is currently being evaluated in a phase II clinical study.

DNA sequences proximal to human mitochondrial DNA deletion breakpoints prevalent in human disease form G-quadruplexes, a class of DNA structures inefficiently unwound by the mitochondrial replicative Twinkle helicase

Mitochondrial DNA deletions are prominent in human genetic disorders, cancer, and aging. It is thought that stalling of the mitochondrial replication machinery during DNA synthesis is a prominent source of mitochondrial genome instability; however, the precise molecular determinants of defective mitochondrial replication are not well understood. In this work, we performed a computational analysis of the human mitochondrial genome using the "Pattern Finder" G-quadruplex (G4) predictor algorithm to assess whether G4-forming sequences reside in close proximity (within 20 base pairs) to known mitochondrial DNA deletion breakpoints. We then used this information to map G4P sequences with deletions characteristic of representative mitochondrial genetic disorders and also those identified in various cancers and aging. Circular dichroism and UV spectral analysis demonstrated that mitochondrial G-rich sequences near deletion breakpoints prevalent in human disease form G-quadruplex DNA structures. A biochemical analysis of purified recombinant human Twinkle protein (gene product of c10orf2) showed that the mitochondrial replicative helicase inefficiently unwinds well characterized intermolecular and intramolecular G-quadruplex DNA substrates, as well as a unimolecular G4 substrate derived from a mitochondrial sequence that nests a deletion breakpoint described in human renal cell carcinoma. Although G4 has been implicated in the initiation of mitochondrial DNA replication, our current findings suggest that mitochondrial G-quadruplexes are also likely to be a source of instability for the mitochondrial genome by perturbing the normal progression of the mitochondrial replication machinery, including DNA unwinding by Twinkle helicase.

Study of insulin resistance in cybrid cells harboring diabetes-susceptible and diabetes-protective mitochondrial haplogroups

AIM

This study aims to elucidate the independent role of mitochondria in the pathogenesis of insulin resistance (IR).

METHODS

Cybrids derived from 143B osteosarcoma cell line and harboring the same nuclear DNA but different mitochondrial haplogroups were studied. Cybrid B4 (the major diabetes-susceptible haplogroup in Chinese population), cybrid D4 (the major diabetes-resistant haplogroup in Chinese population) and cybrid N9 (the diabetes-resistant haplogroup in Japanese population) were cultured in a medium containing 25 mM glucose and stimulated with 0 μM, 0.1 μM, and 1.0 μM insulin. We compared the insulin activation of PI3K-Akt (glucose uptake) and ERK-MAPK (pro-inflammation) signaling pathways, intracellular and mitochondrial oxidative stress (DCF and MitoSOX Red), and their responses to the antioxidant N-acetylcysteine (NAC).

RESULTS

Upon insulin treatment, the translocation of cytoplasmic GLUT1/GLUT4 to the cell membrane in cybrid D4 and N9 cells increased significantly, whereas the changes in B4 cells were not or less significant. On the contrary, the ratio of insulin-induced JNK and P38 to Akt phosphorylation was significantly greater in cybrid B4 cells than in cybrid D4 and N9 cells. The levels of DCF and MitoSOX Red, which are indicative of the oxidative stress, were significantly higher in the B4 cells in basal conditions and after insulin treatment. Following treatment with the antioxidant NAC, cybrid B4 cells showed significantly reduced insulin-induced phosphorylation of P38 and increased GLUT1/GLUT4 translocation to the cell membrane, suggesting that NAC may divert insulin signaling from pro-inflammation to glucose uptake.

CONCLUSIONS

Mitochondria play an independent role in the pathogenesis of IR, possibly through altered production of intracellular ROS.

Neuromuscular and systemic presentations in adults: diagnoses beyond MERRF and MELAS

Mitochondrial diseases are a diverse group of inherited and acquired disorders that result in inadequate energy production. They can be caused by inheritable genetic mutations, acquired somatic mutations, and exposure to toxins (including some prescription medications). Normal mitochondrial physiology is responsible, in part, for the aging process itself, as free radical production within the mitochondria results in a lifetime burden of oxidative damage to DNA, especially the mitochondrial DNA that, in turn, replicate the mutational burden in future copies of itself, and lipid membranes. Primary mitochondrial diseases are those caused by mutations in genes that encode for mitochondrial structural and enzymatic proteins, and those proteins required for mitochondrial assembly and maintenance. A number of common adult maladies are associated with defective mitochondrial energy production and function, including diabetes, obesity, hyperthyroidism, hypothyroidism, and hyperlipidemia. Mitochondrial dysfunction has been demonstrated in many neurodegenerative disorders, including Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and some cancers. Polymorphisms in mitochondrial DNA have been linked to disease susceptibility, including death from sepsis and survival after head injury. There is considerable overlap in symptoms caused by primary mitochondrial diseases and those illnesses that affect mitochondrial function, but are not caused by primary mutations, as well as disorders that mimic mitochondrial diseases, but are caused by other identified mutations. Evaluation of these disorders is complex, expensive, and not without false-negative and false-positive results that can mislead the physician. Most of the common heritable mitochondrial disorders have been well-described in the literature, but can be overlooked by many clinicians if they are uneducated about these disorders. In general, the evaluation of the classic mitochondrial disorders has become straightforward if the clinician recognized the phenotype and orders appropriate confirmatory testing. However, the majority of patients referred for a mitochondrial evaluation do not have a clear presentation that allows for rapid identification and testing. This article provides introductory comments on mitochondrial structure, physiology, and genetics, but will focus on the presentation and evaluation of adults with mitochondrial symptoms, but who may not have a primary mitochondrial disease.

Mutation C3256T of mitochondrial genome in white blood cells: novel genetic marker of atherosclerosis and coronary heart disease

This study was undertaken to examine the association between the level of heteroplasmy for the mutation C3256T in human white blood cells and the extent of carotid atherosclerosis, as well as the presence of coronary heart disease (CHD), the major clinical manifestation of atherosclerosis. Totally, 191 participants (84 men, 107 women) aged 65.0 years (SD 9.4) were recruited in the study; 45 (24%) of them had CHD. High-resolution B-mode ultrasonography of carotids was used to estimate the extent of carotid atherosclerosis by measuring of the carotid intima-media thickness (cIMT). DNA samples were obtained from whole venous blood, and then PCR and pyrosequencing were carried out. On the basis of pyrosequencing data, the levels of C3256T heteroplasmy in DNA samples were calculated. The presence of the mutant allele was detected in all study participants; the level of C3256T heteroplasmy in white blood cells ranged from 5% to 74%. The highly significant relationship between C3256T heteroplasmy level and predisposition to atherosclerosis was revealed. In individuals with low predisposition to atherosclerosis the mean level of C3256T heteroplasmy was 16.8%, as compared to 23.8% in moderately predisposed subjects, and further to 25.2% and 28.3% in significantly and highly predisposed subjects, respectively. The level of C3256T heteroplasmy of mitochondrial genome in human white blood cells is a biomarker of mitochondrial dysfunction and risk factor for atherosclerosis; therefore, it can be used as an informative marker of genetic susceptibility to atherosclerosis, coronary heart disease and myocardial infarction.

Mitochondrial DNA coding and control region variants as genetic risk factors for type 2 diabetes

Both the coding and control regions of mitochondrial DNA (mtDNA) play roles in the generation of diabetes; however, no studies have thoroughly reported on the combined diabetogenic effects of variants in the two regions. We determined the mitochondrial haplogroup and the mtDNA sequence of the control region in 859 subjects with diabetes and 1,151 normoglycemic control subjects. Full-length mtDNA sequences were conducted in 40 subjects harboring specific diabetes-related haplogroups. Multivariate logistic regression analysis with adjustment for age, sex, and BMI revealed that subjects harboring the mitochondrial haplogroup B4 have significant association with diabetes (DM) (odds ratio [OR], 1.54 [95% CI 1.18-2.02]; P < 0.001), whereas subjects harboring D4 have borderline resistance against DM generation (0.68 [0.49-0.94]; P = 0.02). Upon further study, we identified an mtDNA composite group susceptible to DM generation consisting of a 10398A allele at the coding region and a polycytosine variant at nucleotide pair 16184-16193 of the control region, as well as a resistant group consisting of C5178A, A10398G, and T152C variants. The OR for susceptible group is 1.31 (95% CI 1.04-1.67; P = 0.024) and for the resistant group is 0.48 (0.31-0.75; P = 0.001). Our study found that mtDNA variants in the coding and control regions can have combined effects influencing diabetes generation.

Taurine supplementation restored the changes in pancreatic islet mitochondria in the fetal protein-malnourished rat

Intra-uterine growth retardation has been linked to the development of type 2 diabetes in later life. Mitochondrial changes have been suggested as a link between fetal malnutrition and adult insulin resistance. Taurine has been implicated in this process. We investigated whether protein malnutrition in early life alters mitochondria of the pancreatic islets in adulthood, and whether taurine supplementation restores these changes. Male offspring of rats fed a control diet, a low-protein diet or a low-protein diet supplemented with taurine during pregnancy and lactation were weaned onto the control diet. In each group, at 20 weeks of age, intravenous glucose tolerance tests, euglycaemic–hyperinsulinaemic clamp studies, morphometric analysis of the pancreatic islets and ultra-structural analysis of the mitochondria of the β-cells were performed. The expressions of cytochrome c oxidase (COX) I and mitochondrial respiratory chain complex II were also measured. Fetal protein-malnourished rats showed decreased pancreatic islet mass and reduced insulin-secretory responses to a glucose load. These rats also showed reduced mitochondrial DNA-encoded COX I gene expression in the islets. Electron microscopic examination showed abnormal mitochondrial shapes in the β-cells of fetal protein-malnourished rats. Taurine supplementation to the low-protein diet restored all these changes. Our findings indicate that a maternal protein-restriction diet causes long-lasting mitochondrial changes that may contribute to the development of type 2 diabetes later in life. The lack of taurine may be a key causative factor for these dysfunctional mitochondrial changes.

Increased protein nitration in mitochondrial diseases: evidence for vessel wall involvement

Mitochondrial diseases (MD) are heterogeneous disorders because of impairment of respiratory chain function leading to oxidative stress. We hypothesized that in MD the vascular endothelium may be affected by increased oxidative/nitrative stress causing a reduction of nitric oxide availability. We therefore, investigated the pathobiology of vasculature in MD patients by assaying the presence of 3-nitrotyrosine in muscle biopsies followed by the proteomic identification of proteins which undergo tyrosine nitration. We then measured the flow-mediated vasodilatation as a proof of altered nitric oxide generation/bioactivity. Here, we show that 3-nitrotyrosine staining is specifically located in the small vessels of muscle tissue and that the reaction is stronger and more evident in a significant percentage of vessels from MD patients as compared with controls. Eleven specific proteins which are nitrated under pathological conditions were identified; most of them are involved in energy metabolism and are located mainly in mitochondria. In MD patients the flow-mediated vasodilatation was reduced whereas baseline arterial diameters, blood flow velocity and endothelium-independent vasodilatation were similar to controls. The present results provide evidence that in MD the vessel wall is a target of increased oxidative/nitrative stress.

Mitochondrial DNA variants in the pathogenesis of type 2 diabetes - relevance of asian population studies

Mitochondrial dysfunction involves defective insulin secretion by pancreatic beta-cells, and insulin resistance in insulin-sensitive tissues such as muscle and adipose tissue. Mitochondria are recognized as the most important cellular source of energy, and the major generator of intracellular reactive oxygen species (ROS). Intracellular antioxidative systems have been developed to cope with increased oxidative damage. In case of minor oxidative stress, the cells may increase the number of mitochondria to produce more energy. A mechanism called mitochondrial biogenesis, involving several transcription factors and regulators, controls the quantity of mitochondria. When oxidative damage is advanced beyond the repair capacity of antioxidative systems, then oxidative stress can lead to cell death. Therefore, this organelle is central to cell life or death. Available evidence increasingly shows genetic linkage between mitochondrial DNA (mtDNA) alterations and type 2 diabetes (T2D). Based on previous studies, the mtDNA 16189 variant is associated with metabolic syndrome, higher fasting insulin concentration, insulin resistance index and lacunar cerebral infarction. These data support the involvement of mitochondrial genetic variation in the pathogenesis of T2D. Importantly, phylogeographic studies of the human mtDNAs have revealed that the human mtDNA tree is rooted in Africa and radiates into different geographic regions and can be grouped as haplogroups. The Asian populations carry very different mtDNA haplogroups as compared to European populations. Therefore, it is critically important to determine the role of mtDNA polymorphisms in T2D.

Emerging roles of mitochondrial membrane dynamics in health and disease

Mitochondria are highly dynamic organelles forming a tubular network that is sustained by fusion and fission events. Impairment thereof leads to various neuropathies in humans, such as optic atrophy and Parkinson's disease. We have only begun to understand the molecular machineries facilitating fusion and fission of mitochondria and how these processes are regulated. The physiological role of mitochondrial dynamics and how it may be involved in maintaining mitochondrial functionality is still unclear. Here, we discuss current views in this emerging field focusing on the molecular basis of how mitochondrial morphology is regulated and how this may contribute to mitochondrial quality control.

A gel electrophoresis method for detection of mitochondrial DNA mutation (3243 tRNALeu (UUR)) applied to a Norwegian family with diabetes mellitus and hearing loss

Blood cells of selected patients from a large Norwegian family with maternally transmitted diabetes mellitus, hearing loss and muscular dysfunction were screened for possible A3243G mutation tRNA(Leu (UUR)) in mitochondrial DNA. We selected 7 patients from 3 of the 4 generations of the family and 10 unrelated healthy control subjects for mutation analysis using denaturing gradient gel electrophoresis (DGGE) and both manual and automated DNA sequencing. The A3243G mutation was found in peripheral blood cells of all 7 patients, but in none of the controls. The mutation was in the form of heteroplasmy and the amount of mutant DNA was found to be between 10% and 35% of total mtDNA in individual patients. This is the first report of a Norwegian family with maternally inherited diabetes and hearing loss carrying the A3243G mutation in mitochondrial DNA.

Ciliary neurotrophic factor (CNTF) signals through STAT3-SOCS3 pathway and protects rat pancreatic islets from cytokine-induced apoptosis

CNTF is a cytokine that promotes survival and/or differentiation in many cell types, including rat pancreatic islets. In this work, we studied the mechanism of CNTF signal in neonatal rats pancreatic islets isolated by the collagenase method and cultured for 3 days in RPMI medium without (CTL) or with 1 nM of CNTF. The medium contained, when necessary, specific inhibitors of the PI3K, MAPK and JAK/STAT3 pathways. mRNA expression (RT-PCR) and protein phosphorylation (Western blot) of Akt, ERK1/2 and STAT3, and SOCS-3 (RT-PCR and Western blot), as well as glucose-stimulated insulin secretion (GSIS) (Radioimmunoassay), were analyzed. Our results showed that Akt, ERK1 and STAT3 mRNA expression, as well as phosphorylated Akt and ERK1/2, was not affected by CNTF treatment. CNTF increased cytoplasmatic and nuclear phosphorylated STAT3, and the SOCS3 mRNA and protein expression. In addition, CNTF lowered apoptosis and impaired GSIS. These effects were blocked by the JAK inhibitor, AG490 and by the STAT3 inhibitor Curcumin, but not by the MAPK inhibitor, PD98059, nor by the PI3K inhibitor, Wortmannin. In conclusion, CNTF signals through the JAK2/STAT3 cascade, increases SOCS3 expression, impairs GSIS and protects neonatal pancreatic rat islets from cytokine-induced apoptosis. These findings indicate that CNTF may be a potential therapeutic tool against Type 1 and/or Type 2 diabetes.

Batteries not included: diagnosis and management of mitochondrial disease

In 1998, Wallace et al. (Science 1988; 242: 1427-30) published evidence that the mutation m.11778G>A was responsible for causing Leber's hereditary optic neuropathy. This was the first account of a mitochondrial DNA mutation being irrefutably linked with a human disease and was swiftly followed by a report from Holt et al. (Nature 1988; 331: 717-9) identifying deletions in mitochondrial DNA as a cause for myopathy. During the subsequent 20 years there has been an exponential growth in 'mitochondrial medicine', with clinical, biochemical and genetic characterizations of a wide range of mitochondrial diseases and evidence implicating mitochondria in a host of many other clinical conditions including ageing, neurodegenerative illness and cancer. In this review we shall focus on the diagnosis and management of mitochondrial diseases that lead directly or indirectly to disruption of the process of oxidative phosphorylation.

A detailed investigation of maternally inherited diabetes and deafness (MIDD) including clinical characteristics, C-peptide secretion, HLA-DR and -DQ status and autoantibody pattern

BACKGROUND

This article presents a clinically characterization of the mitochondrial DNA mutation (A3243G) associated with maternally inherited diabetes and deafness (MIDD) syndrome in two families.

METHODS

Six patients with MIDD and one mutation-positive relative with normal glucose tolerance (NGT) were examined. Fasting serum C-peptide was measured in all subjects and compared with controls having NGT (n = 14). C-peptide response to an intravenous glucose tolerance test (IVGTT) was investigated in the diabetic patients not treated with insulin (n = 3) and in the mutation-positive healthy individual and compared with the controls.

RESULTS

The A3243G heteroplasmy value varied between 5 and 30%. All A3243G carriers had HLA-DR1-DQ5 haplotype, and either the -DQ5 or the -DQ6 allele. The fasting and the serum C-peptide levels at 120 min during the IVGTT did not differ between the A3243G carriers and the controls. A missing first phase and a decreased total C-peptide response was detected in the mutation-positive diabetics compared with controls (p < 0.0001). The same abnormality was found in the A3243G carrier with NGT. Circulating islet cell antibody (ICA) was present in three patients with MIDD. Glutamic acid decarboxylase (GAD), tyrosine phosphatase-like protein IA-2 (IA-2) and mitochondrial antibodies were missing. The diagnosis of MIDD was delayed in each case.

CONCLUSIONS

A missing first phase and a decreased total C-peptide response during an IVGTT was characteristic for the A3243G mutation. The fasting C-peptide level of the carriers did not differ from the controls. Circulating ICA was present in some patients, but GAD, IA-2 and mitochondrial antibodies were absent. All subjects had HLA-DR1-DQ5 haplotype, and either -DQ5 or -DQ6 alleles.

Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes: basic concepts, clinical phenotype, and therapeutic management of MELAS syndrome

Since the initial description almost 25 years ago, the syndrome of mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS) has been a useful model to study the complex interplay of factors that define mitochondrial disease. This syndrome, most commonly caused by an A-to-G transition mutation at position 3243 of the mitochondrial genome, is typified by characteristic neurological manifestations including seizures, encephalopathy, and strokelike episodes, as well as other frequent secondary manifestations including short stature, cognitive impairment, migraines, depression, cardiomyopathy, cardiac conduction defects, and diabetes mellitus. In this review, we discuss the history, pathogenesis, clinical features, and diagnostic and management strategies of mitochondrial disease in general and of MELAS in particular. We explore features of mitochondrial genetics, including the concepts of heteroplasmy, mitotic segregation, and threshold effect, as a basis for understanding the variability and complicated inheritance patterns seen with this group of diseases. We also describe systemic manifestations of MELAS-associated mutations, including cardiac, renal, endocrine, gastrointestinal, and endothelial abnormalities and pathology, as well as the hypothetical role of derangements to COX enzymatic function in driving the unique pathology and clinical manifestations of MELAS. Although therapeutic options for MELAS and other mitochondrial diseases remain limited, and recent trials have been disappointing, we also consider current and potential therapeutic modalities.

Testicular mitochondrial alterations in untreated streptozotocin-induced diabetic rats

Diabetes-induced complications are associated with mitochondrial dysfunction and increasing evidence suggests that diabetes has an adverse effect on male reproductive function. The STZ-induced diabetic rat was used as an animal model for the type 1 form of the disease with the aim of determining its effects in spermatogenesis and testicular mitochondrial function. Several aspects of mitochondrial function were measured, including respiratory and electric potential function, as well as mitochondrial calcium loading capacity. Additionally oxidative stress production, antioxidant levels and possible apoptotic alterations were also evaluated. We observed that diabetic animals present alterations in spermatogenesis in both the testis and epidydimus. However, and surprisingly, the overall results in mitochondrial parameters failed to reveal severe testicular mitochondrial dysfunction in diabetic animals, with the exception of a decrease in calcium load. Taken together, results suggest that in animal models that mimic untreated type 1 diabetes the severe effects of the condition on spermatogenesis are not directly mitochondrial-mediated.

Renal function and mitochondrial cytopathy (MC): more questions than answers?

Our knowledge of mitochondrial biology has advanced significantly in the last 10 years. The effects of mitochondrial dysfunction or cytopathy (MC) on the heart and neuromuscular system are well known, and its involvement in the pathophysiology of several common clinical disorders such as diabetes, hyperlipidaemia and hypertension, is just beginning to emerge; however, its contribution to renal disease has received much less attention, and the available literature raises some interesting questions: Why do children with MC commonly present with a renal phenotype that is often quite different from adults? How does a mutation in mitochondrial DNA (mtDNA) lead to disease at the cellular level, and how can a single mtDNA point mutation result in such a variety of renal- and non-renal phenotypes in isolation or combined? Why are some regions of the nephron seemingly more sensitive to mitochondrial dysfunction and damage by mitochondrial toxins? Perhaps most important of all, what can be done to diagnose and treat MC, now and in the future? In this review we summarize our current understanding of the relationship between mitochondrial biology, renal physiology and clinical nephrology, in an attempt to try to answer some of these questions. Although MC is usually considered a rare defect, it is almost certainly under-diagnosed. A greater awareness and understanding of kidney involvement in MC might lead to new treatment strategies for diseases in which mitochondrial dysfunction is secondary to toxic or ischaemic injury, rather than to an underlying genetic mutation.

Clinical features, diagnosis and management of maternally inherited diabetes and deafness (MIDD) associated with the 3243A>G mitochondrial point mutation

Maternally inherited diabetes and deafness (MIDD) affects up to 1% of patients with diabetes but is often unrecognized by physicians. It is important to make an accurate genetic diagnosis, as there are implications for clinical investigation, diagnosis, management and genetic counselling. This review summarizes the range of clinical phenotypes associated with MIDD; outlines the advances in genetic diagnosis and pathogenesis of MIDD; summarizes the published prevalence data and provides guidance on the clinical management of these patients and their families.

Genetic, pathogenetic, and phenotypic implications of the mitochondrial A3243G tRNALeu(UUR) mutation

Mitochondrial disorders are frequently caused by mutations in mitochondrial genes and usually present as multisystem disease. One of the most frequent mitochondrial mutations is the A3,243G transition in the tRNALeu(UUR) gene. The phenotypic expression of the mutation is variable and comprises syndromic or non-syndromic mitochondrial disorders. Among the syndromic manifestations the mitochondrial encephalopathy, lactacidosis, and stroke-like episode (MELAS) syndrome is the most frequent. In single cases the A3,243G mutation may be associated with maternally inherited diabetes and deafness syndrome, myoclonic epilepsy and ragged-red fibers (MERRF) syndrome, MELAS/MERRF overlap syndrome, maternally inherited Leigh syndrome, chronic external ophthalmoplegia, or Kearns-Sayre syndrome. The wide phenotypic variability of the mutation is explained by the peculiarities of the mitochondrial DNA, such as heteroplasmy and mitotic segregation, resulting in different mutation loads in different tissues and family members. Moreover, there is some evidence that additional mtDNA sequence variations (polymorphisms, haplotypes) influence the phenotype of the A3,243G mutation. This review aims to give an overview on the actual knowledge about the genetic, pathogenetic, and phenotypic implications of the A3,243G mtDNA mutation.

Mutational analysis of the mitochondrial tRNALeu(UUR) gene in Tunisian patients with mitochondrial diseases

The mitochondrial tRNA(Leu(UUR)) gene (MTTL) is a hot spot for pathogenic mutations that are associated with mitochondrial diseases with various clinical features. Among these mutations, the A3243G mutation was associated with various types of mitochondrial multisystem disorders, such as MIDD, MELAS, MERRF, PEO, hypertrophic cardiomyopathy, and a subtype of Leigh syndrome. We screened 128 Tunisian patients for the A3243G mutation in the mitochondrial tRNA(Leu(UUR)) gene. This screening was carried out using PCR-RFLP with the restriction endonuclease ApaI. None of the 128 patients or the 100 controls tested were found to carry the mitochondrial A3243G mutation in the tRNA(Leu(UUR)) gene in homoplasmic or heteroplasmic form. After direct sequencing of the entire mitochondrial tRNA(Leu(UUR)) gene and a part of the mitochondrial NADH dehydrogenase 1, we found neither mutations nor polymorphisms in the MTTL1 gene in the tested patients and controls, and we confirmed the absence of the A3243G mutation in this gene. We also found a T3396C transition in the ND1 gene in one family with NSHL which was absent in the other patients and in 100 controls. Neither polymorphisms nor other mutations were found in the mitochondrial tRNA(Leu(UUR)) gene in the tested patients.

Mitochondrial Disease—Its Impact, Etiology, and Pathology

Mitochondria are ubiquitous organelles that are intimately involved in many cellular processes, but whose principal task is to provide the energy necessary for normal cell functioning and maintenance. Disruption of this energy supply can have devastating consequences for the cell, organ, and individual. Over the last two decades, mutations in both mitochondrial DNA (mtDNA) and nuclear DNA have been identified as causative in a number of well-characterized clinical syndromes, although for mtDNA mutations in particular, this relationship between genotype and phenotype is often not straightforward. Despite this, a number of epidemiological studies have been undertaken to assess the prevalence of mtDNA mutations and these have highlighted the impact that mtDNA disease has on both the community and individual families. Although there has been considerable improvement in the diagnosis of mitochondrial disorders, disappointingly this has not been matched by developments toward effective treatment. Nevertheless, our understanding of mitochondrial biology is gathering pace and progress in this area will be crucial to devising future treatment strategies. In addition to mitochondrial disease, evidence for a central role of mitochondria in other processes, such as aging and neurodegeneration, is slowly accumulating, although their role in cancer remains controversial. In this chapter, we discuss these issues and offer our own views based on our cumulative experience of investigating and managing these diseases over the last 20 years.

Mitochondrial complex I activity is significantly decreased in a patient with maternally inherited type 2 diabetes mellitus and hypertrophic cardiomyopathy associated with mitochondrial DNA C3310T mutation: a cybrid study

Mitochondrial respiratory function in a patient with maternally inherited type 2 diabetes mellitus and hypertrophic cardiomyopathy associated with heteroplasmic mitochondrial DNA (mtDNA) C3310T mutation, which replaces the second amino acid of NADH dehydrogenase 1 (ND1) from a hydrophobic Proline to a hydrophilic Serine, was investigated. Mitochondrial respiratory function solely due to mtDNA C3310T mutation was investigated in cybrid system by the fusion of mtDNA-deleted (rho(0)) HeLa cells and exogenous mtDNA either from the proband or from controls. Total oxygen consumption of the proband cybrid cells was significantly decreased compared with those of controls (2.468+/-0.475 versus 2.871+/-0.484 micromol/h/10(7) cells, p=0.0392). Mitochondrial respiratory chain complex I activity of the proband cybrid cells was also significantly decreased compared with those of controls (0.191+/-0.080 versus 0.288+/-0.113 micromol/h/mg protein, p=0.0223). Furthermore, ATP content in the proband cybrid cells was also significantly decreased compared with those in controls (1.119+/-0.344 versus 1.419+/-0.378 pmol/10(5) cells, p=0.044). The present study indicates that mtDNA C3310T mutation may be a pathogenic mutation of maternally inherited type 2 diabetes mellitus and hypertrophic cardiomyopathy in the proband and the family.

Functional Delivery of a Cytosolic tRNA into Mutant Mitochondria of Human Cells

Many maternally inherited and incurable neuromyopathies are caused by mutations in mitochondrial (mt) transfer RNA (tRNA) genes. Kinetoplastid protozoa, including Leishmania, have evolved specialized systems for importing nucleus-encoded tRNAs into mitochondria. We found that the Leishmania RNA import complex (RIC) could enter human cells by a caveolin-1-dependent pathway, where it induced import of endogenous cytosolic tRNAs, including tRNA(Lys), and restored mitochondrial function in a cybrid harboring a mutant mt tRNA(Lys) (MT-TK) gene. The use of protein complexes to modulate mitochondrial function may help in the management of such genetic disorders.

A novel mitochondrial DNA missense mutation at G3421A in a family with maternally inherited diabetes and deafness

OBJECTIVE

Mutations in mtDNA are thought to be responsible for the pathogenesis of maternally inherited diabetes. Here, we report a family with maternally inherited diabetes and deafness whose members did not harbour the mtDNA A3243G mutation, the most frequent point mutation in mitochondrial diabetic patients. This study aimed to investigate a possible other mtDNA mutation and its prevalence in type 2 diabetic patients.

METHODS

Height, body weight, waistline, and hip circumference were measured and serum biochemical marks determined in all members of the family. In addition, a 75 g oral glucose tolerance test and electric listening test were conducted in these members. Genomic DNA was prepared from peripheral leukocytes. Direct sequencing of PCR products was used to detect the mtDNA mutation in this family. The prevalence of mtDNA G3421A nucleotide substitutions was investigated by restriction fragment length polymorphism analysis in 1350 unrelated type 2 diabetic patients recruited by random cluster sampling from the central city area of Shanghai, China.

RESULTS

(1) A new missense homoplasmic mutation of mtDNA G3421A was found in a maternally inherited diabetic family and existed neither in 1350 unrelated type 2 diabetic patients nor in 50 non-diabetic individuals. (2) The mode of mutation and diabetes transmission was typical maternal inheritance in this family. (3) All diabetic family members were found to have an onset at 35-42 years of age, accompanied by deafness of varying degrees.

CONCLUSION

mtDNA G3421A (Val39Ile) found in a family with maternally inherited diabetes and deafness is a novel missense mutation. Whether this is a diabetogenic mutation and its effect on mitochondrial function needs to be further studied.

The European-specific mitochondrial cluster J/T could confer an increased risk of insulin-resistance and type 2 diabetes: an analysis of the m.4216T > C and m.4917A > G variants

The aims of this study were to investigate the contributions of the mitochondrial DNA m.4216T > C and m.4917A > G variants, and also of the European-specific mitochondrial cluster J/T, to the development of type 2 diabetes mellitus in Caucasian-Brazilian patients from Southern Brazil. We analyzed 347 type 2 diabetes patients and 350 control subjects. Variant frequencies in patients and control subjects were compared using chi2 tests or odds ratio. We also compared clinical and laboratory characteristics among patients with and without the variants. We found that the frequencies of the m.4216T > C and m.4917A > G variants are higher in diabetic patients than in control subjects. Moreover, haplogroups J (partially defined by the presence of the m.4216T > C variant only) and T (partially defined by the presence of both m.4216T > C and m.4917A > G variants) are more frequent in the type 2 diabetic group than in the control group. Patients belonging to the cluster J/T are more insulin resistant than patients of other haplogroups. In conclusion, our results indicate the association of the cluster J/T (as suggested by analyses of the m.4216T > C and m.4917A > G variants) with insulin resistance and type 2 diabetes.

Epidemiology of pediatric mitochondrial respiratory chain disorders in northwest Spain

Our knowledge of mitochondrial respiratory chain diseases has increased dramatically in recent years, but relatively little information is available about their prevalence and incidence, either in pediatric or adult patients. This study reports incidence and prevalence estimates, and summarizes the clinical, biochemical, histologic, and genetic characteristics of 51 patients age 0-16 years. The overall annual incidence of all mitochondrial respiratory chain diseases was estimated to be 1.43 cases per 10(5) in the population as a whole, and 2.85 cases per 10(5) in the under-6 population. The overall prevalence of all mitochondrial respiratory chain diseases was estimated as 7.5 cases per 10(5) in the under-19 population, and 8.7 cases per 10(5) in the under-16 population. These incidence and prevalence estimates are higher than in most previous studies of pediatric populations. Estimated prevalences of specific mitochondrial respiratory chain diseases were 2.05 cases per 10(5) for Leigh syndrome, 0.68 per 10(5) for mitochondrial deoxyribonucleic acid (mtDNA) deletions and deletions-duplications, 1.59 per 10(5) for mtDNA depletions, and 0.45 per 10(5) for mtDNA point mutations. Leigh syndrome was the most frequent clinical syndrome. The estimates of the prevalences of mtDNA deletions, deletions-duplications, and point mutations set forth here are lower than in similar previous studies, whereas the estimate of the prevalence of mtDNA depletions is rather higher. Sixteen of these patients manifested phenotypic syndromes that have not been previously reported in association with mitochondrial respiratory chain diseases.