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

Morphometric, subcellular, in vitro fertilisation and embryonic developmental assessment of mouse oocytes produced by anti-inhibin serum or pregnant mare serum gonadotrophin superovulation

This study compared the morphometric, subcellular characteristics, in vitro fertilisation (IVF) and embryonic developmental potential of metaphase II (MII) mouse oocytes obtained from females superovulated with either anti-inhibin serum-human chorionic gonadotrophin (AIS-hCG) or pregnant mare serum gonadotrophin (PMSG)-hCG. The oocyte's quantity, quality, zona pellucida (ZP) thickness, perivitelline space (PVS), diameter, microtubules, F-actin, cortical granules (CGs) and mitochondrial distribution were determined. Superovulation using AIS-hCG resulted in a higher numbers of oocyte/donor compared with PMSG-hCG (P=0.002). There was no difference in morphologically normal and abnormal oocytes between AIS-hCG and PMSG-hCG (P=0.425 and P=0.194, respectively). The morphometric measurements showed no difference in oocyte diameter between AIS-hCG and PMSG-hCG (P=0.289). However, the thickness of the ZP of oocytes from AIS-hCG females was decreased compared with PMSG-hCG (P<0.001). The PVS of oocytes from the AIS-hCG was larger than with PMSG-hCG (P<0.001). The microtubules of oocytes from both AIS-hCG and PMSG-hCG were normal, although there was an increased fluorescence intensity in the AIS-hCG oocytes (P<0.001). The F-actin and CGs distribution in oocytes from both AIS-hCG and PMSG-hCG were similar (P=0.330 and P=0.13, respectively). Although the oocytes from PMSG-hCG females had homogenously distributed mitochondria, AIS-hCG oocytes showed more peripheral distribution with no differences in fluorescence intensity (P=0.137). The blastocyst development rates after IVF with fresh sperm showed no difference between AIS-hCG and PMSG-hCG (P=0.235). These data suggested that AIS-hCG superovulation produces high numbers of morphologically normal oocytes that also possess normal subcellular structures, good morphological characteristics and had high invitro embryonic developmental potential.

Disentangling the heterogeneity of adulthood-onset non-autoimmune diabetes: a little closer but lot more to do

Diabetes diagnosed in adults is a highly heterogeneous disorder. It mostly consists of what is referred to as type 2 diabetes but also comprises other entities (i.e. different diseases), including latent autoimmune diabetes, late onset forms of monogenic diabetes and familial diabetes of the adulthood, which has recently been the source of new diabetogenes discovery. Notably, type 2 diabetes is itself heterogeneous as it includes subtypes with onset at the extremes of age and/or weight distributions characterized by different degree of hyperglycemia and cardiovascular risk as compared to common forms of type 2 diabetes occurring in middle-aged, overweight/obese individuals. Understanding whether these are different presentations of one, highly heterogeneous disease or separate nosological entities with different clinical trajectories and requiring different treatments is essential to effectively pursue the path of precision medicine.

Neuro-ophthalmic manifestations of mitochondrial disorders and their management

The visual system has high metabolic requirements and is therefore particularly vulnerable to mitochondrial dysfunction. The most commonly affected tissues include the extraocular muscles, photoreceptors, retinal pigment epithelium, optic nerve and visual cortex. Hence, the most common manifestations of mitochondrial disorders are progressive external ophthalmoplegia, macular pattern dystrophy, pigmentary retinopathy, optic neuropathy and retrochiasmal visual field loss. With the exception of Leber hereditary optic neuropathy and stroke-like episodes seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes, the majority of neuro-ophthalmic manifestations have an insidious onset. As such, some patients may not recognize subtle progressive visual symptoms. When mitochondrial disorders are highly suspected, meticulous examination performed by an ophthalmologist with targeted ancillary testing can help confirm the diagnosis. Similarly, neuro-ophthalmic symptoms and signs may be the first indication of mitochondrial disease and should prompt systemic investigations for potentially life-threatening associations, such as cardiac conduction defects. Finally, the ophthalmologist can offer symptomatic treatments for some of the most disabling manifestations of these disorders.

Monogenic Diabetes: From Genetic Insights to Population-Based Precision in Care. Reflections From a Diabetes Care Editors' Expert Forum

Individualization of therapy based on a person's specific type of diabetes is one key element of a "precision medicine" approach to diabetes care. However, applying such an approach remains difficult because of barriers such as disease heterogeneity, difficulties in accurately diagnosing different types of diabetes, multiple genetic influences, incomplete understanding of pathophysiology, limitations of current therapies, and environmental, social, and psychological factors. Monogenic diabetes, for which single gene mutations are causal, is the category most suited to a precision approach. The pathophysiological mechanisms of monogenic diabetes are understood better than those of any other form of diabetes. Thus, this category offers the advantage of accurate diagnosis of nonoverlapping etiological subgroups for which specific interventions can be applied. Although representing a small proportion of all diabetes cases, monogenic forms present an opportunity to demonstrate the feasibility of precision medicine strategies. In June 2019, the editors of Diabetes Care convened a panel of experts to discuss this opportunity. This article summarizes the major themes that arose at that forum. It presents an overview of the common causes of monogenic diabetes, describes some challenges in identifying and treating these disorders, and reports experience with various approaches to screening, diagnosis, and management. This article complements a larger American Diabetes Association effort supporting implementation of precision medicine for monogenic diabetes, which could serve as a platform for a broader initiative to apply more precise tactics to treating the more common forms of diabetes.

Overview of Atypical Diabetes

Although type 1 diabetes mellitus and, to a lesser extent, type 2 diabetes mellitus, are the prevailing forms of diabetes in youth, atypical forms of diabetes are not uncommon and may require etiology-specific therapies. By some estimates, up to 6.5% of children with diabetes have monogenic forms. Mitochondrial diabetes and cystic fibrosis related diabetes are less common but often noted in the underlying disease. Atypical diabetes should be considered in patients with a known disorder associated with diabetes, aged less than 25 years with nonautoimmune diabetes and without typical characteristics of type 2 diabetes mellitus, and/or with comorbidities associated with atypical diabetes.

Clinical features of mtDNA-related syndromes in adulthood

Mitochondrial diseases are the most common inheritable metabolic diseases, due to defects in oxidative phosphorylation. They are caused by mutations of nuclear or mitochondrial DNA in genes involved in mitochondrial function. The peculiarity of "mitochondrial DNA genetics rules" in part explains the marked phenotypic variability, the complexity of genotype-phenotype correlations and the challenge of genetic counseling. The new massive genetic sequencing technologies have changed the diagnostic approach, enhancing mitochondrial DNA-related syndromes diagnosis and often avoiding the need of a tissue biopsy. Here we present the most common phenotypes associated with a mitochondrial DNA mutation with the recent advances in diagnosis and in therapeutic perspectives.

Precision medicine in diabetes: a Consensus Report from the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD)

The convergence of advances in medical science, human biology, data science and technology has enabled the generation of new insights into the phenotype known as 'diabetes'. Increased knowledge of this condition has emerged from populations around the world, illuminating the differences in how diabetes presents, its variable prevalence and how best practice in treatment varies between populations. In parallel, focus has been placed on the development of tools for the application of precision medicine to numerous conditions. This Consensus Report presents the American Diabetes Association (ADA) Precision Medicine in Diabetes Initiative in partnership with the European Association for the Study of Diabetes (EASD), including its mission, the current state of the field and prospects for the future. Expert opinions are presented on areas of precision diagnostics and precision therapeutics (including prevention and treatment) and key barriers to and opportunities for implementation of precision diabetes medicine, with better care and outcomes around the globe, are highlighted. Cases where precision diagnosis is already feasible and effective (i.e. monogenic forms of diabetes) are presented, while the major hurdles to the global implementation of precision diagnosis of complex forms of diabetes are discussed. The situation is similar for precision therapeutics, in which the appropriate therapy will often change over time owing to the manner in which diabetes evolves within individual patients. This Consensus Report describes a foundation for precision diabetes medicine, while highlighting what remains to be done to realise its potential. This, combined with a subsequent, detailed evidence-based review (due 2022), will provide a roadmap for precision medicine in diabetes that helps improve the quality of life for all those with diabetes.

Precision Medicine in Diabetes: A Consensus Report From the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD)

The convergence of advances in medical science, human biology, data science, and technology has enabled the generation of new insights into the phenotype known as "diabetes." Increased knowledge of this condition has emerged from populations around the world, illuminating the differences in how diabetes presents, its variable prevalence, and how best practice in treatment varies between populations. In parallel, focus has been placed on the development of tools for the application of precision medicine to numerous conditions. This Consensus Report presents the American Diabetes Association (ADA) Precision Medicine in Diabetes Initiative in partnership with the European Association for the Study of Diabetes (EASD), including its mission, the current state of the field, and prospects for the future. Expert opinions are presented on areas of precision diagnostics and precision therapeutics (including prevention and treatment), and key barriers to and opportunities for implementation of precision diabetes medicine, with better care and outcomes around the globe, are highlighted. Cases where precision diagnosis is already feasible and effective (i.e., monogenic forms of diabetes) are presented, while the major hurdles to the global implementation of precision diagnosis of complex forms of diabetes are discussed. The situation is similar for precision therapeutics, in which the appropriate therapy will often change over time owing to the manner in which diabetes evolves within individual patients. This Consensus Report describes a foundation for precision diabetes medicine, while highlighting what remains to be done to realize its potential. This, combined with a subsequent, detailed evidence-based review (due 2022), will provide a roadmap for precision medicine in diabetes that helps improve the quality of life for all those with diabetes.

Increased Peripheral Blood Heteroplasmy of the mt.3243A>G Mutation Is Associated with Earlier End-Stage Kidney Disease: A Case Report and Review of the Literature

The mitochondrial DNA mutation mt.3243A>G is most commonly associated with maternally inherited diabetes and deafness (MIM 52,000), but it has protean phenotypes including renal disease due to focal segmental glomerulosclerosis. We describe monozygotic twins who both harboured this mutation and developed ESRD. Although otherwise genetically identical, the twins differed in their peripheral blood leucocyte levels of circulating mt.3243A>G heteroplasmy: 20 versus 10%, when assessed at 42 years of age. The twin with the higher heteroplasmy load developed end-stage kidney disease 15 years earlier than her sister. A review of the published literature supports a relationship between heteroplasmy level and the age at the development of the end stage of renal failure in patients with mt.3243A>G-related kidney disease.

The first concurrent detection of mitochondrial DNA m.3243A>G mutation, deletion, and depletion in a family with mitochondrial diabetes

BACKGROUND

Mitochondrial diabetes (MD) is a rare monogenic form of diabetes and divided into type l and type 2. It is characterized by a strong familial clustering of diabetes with the presence of maternal transmission in conjunction with bilateral hearing impairment in most of the carriers. The most common form of MD is associated with the m.3243A>G mutation in the mitochondrial MT-TL1, but there are also association with a range of other point mutations, deletion, and depletion in mtDNA.

METHODS

The mitochondrial genome anomalies were investigated in a family with clinical features of MD, which includes a proband presenting severe MD conditions including cardiomyopathy, retinopathy, and psychomotor retardation.

RESULTS

By investigating the patient's blood leukocytes and skeletal muscle, we identified the m.3243A>G mutation in heteroplasmic state. This mutation was absent in the rest of the family members. In addition, our analysis revealed in the proband a large mtDNA heteroplasmic deletion (~1 kb) and a reduction in mtDNA copy number.

CONCLUSION

Our study points out, for the first time, a severe phenotypic expression of the m.3243A>G point mutation in association with mtDNA deletion and depletion in MD.

Systematic Genetic Study of Youth With Diabetes in a Single Country Reveals the Prevalence of Diabetes Subtypes, Novel Candidate Genes, and Response to Precision Therapy

Identifying gene variants causing monogenic diabetes (MD) increases understanding of disease etiology and allows for implementation of precision therapy to improve metabolic control and quality of life. Here, we aimed to assess the prevalence of MD in youth with diabetes in Lithuania, uncover potential diabetes-related gene variants, and prospectively introduce precision treatment. First, we assessed all pediatric and most young-adult patients with diabetes in Lithuania (n = 1,209) for diabetes-related autoimmune antibodies. We then screened all antibody-negative patients (n = 153) using targeted high-throughput sequencing of >300 potential candidate genes. In this group, 40.7% had MD, with the highest percentage (100%) in infants (diagnosis at ages 0-12 months), followed by those diagnosed at ages >1-18 years (40.3%) and >18-25 years (22.2%). The overall prevalence of MD in youth with diabetes in Lithuania was 3.5% (1.9% for GCK diabetes, 0.7% for HNF1A, 0.2% for HNF4A and ABCC8, 0.3% for KCNJ11, and 0.1% for INS). Furthermore, we identified likely pathogenic variants in 11 additional genes. Microvascular complications were present in 26% of those with MD. Prospective treatment change was successful in >50% of eligible candidates, with C-peptide >252 pmol/L emerging as the best prognostic factor.

Pathogenic Mitochondria DNA Mutations: Current Detection Tools and Interventions

Mitochondria are best known for their role in energy production, and they are the only mammalian organelles that contain their own genomes. The mitochondrial genome mutation rate is reported to be 10–17 times higher compared to nuclear genomes as a result of oxidative damage caused by reactive oxygen species during oxidative phosphorylation. Pathogenic mitochondrial DNA mutations result in mitochondrial DNA disorders, which are among the most common inherited human diseases. Interventions of mitochondrial DNA disorders involve either the transfer of viable isolated mitochondria to recipient cells or genetically modifying the mitochondrial genome to improve therapeutic outcome. This review outlines the common mitochondrial DNA disorders and the key advances in the past decade necessary to improve the current knowledge on mitochondrial disease intervention. Although it is now 31 years since the first description of patients with pathogenic mitochondrial DNA was reported, the treatment for mitochondrial disease is often inadequate and mostly palliative. Advancements in diagnostic technology improved the molecular diagnosis of previously unresolved cases, and they provide new insight into the pathogenesis and genetic changes in mitochondrial DNA diseases.

Emerging roles of β-cell mitochondria in type-2-diabetes

Type-2-Diabetes (T2D) is the most common metabolic disease in the world today. It erupts as a result of peripheral insulin resistance combined with hyperinsulinemia followed by suppression of insulin secretion from pancreatic β-cells. Mitochondria play a central role in β-cells by sensing glucose and also by mediating the suppression of insulin secretion in T2D. Here, we will summarize the evidence accumulated for the roles of β-cells mitochondria in T2D. We will present an updated view on how mitochondria in β-cells have been associated with T2D, from the genetic, bioenergetic, redox and structural points of view. The emerging picture is that mitochondrial structure and dysfunction directly contribute to β-cell function and in the pathogenesis of T2D.

Monogenic Diabetes: Genetics and Relevance on Diabetes Mellitus Personalized Medicine

BACKGROUND

Diabetes mellitus (DM) is a complex disease with significant impression in today's world. Aside from the most common types recognized over the years, such as type 1 diabetes (T1DM) and type 2 diabetes (T2DM), recent studies have emphasized the crucial role of genetics in DM, allowing the distinction of monogenic diabetes.

METHODS

Authors did a literature search with the purpose of highlighting and clarifying the subtypes of monogenic diabetes, as well as the accredited genetic entities responsible for such phenotypes.

RESULTS

The following subtypes were included in this literature review: maturity-onset diabetes of the young (MODY), neonatal diabetes mellitus (NDM) and maternally inherited diabetes and deafness (MIDD). So far, 14 subtypes of MODY have been identified, while three subtypes have been identified in NDM - transient, permanent, and syndromic.

DISCUSSION

Despite being estimated to affect approximately 2% of all the T2DM patients in Europe, the exact prevalence of MODY is still unknown, accentuating the need for research focused on biomarkers. Consequently, due to its impact in the course of treatment, follow-up of associated complications, and genetic implications for siblings and offspring of affected individuals, it is imperative to diagnose the monogenic forms of DM accurately.

CONCLUSION

Currently, advances in the genetics field allowed the recognition of new DM subtypes, which until now, were considered slight variations of the typical forms. Thus, it is imperative to act in the close interaction between genetics and clinical manifestations, to facilitate diagnosis and individualize treatment.

High Prevalence of a Monogenic Cause in Han Chinese Diagnosed With Type 1 Diabetes, Partly Driven by Nonsyndromic Recessive WFS1 Mutations

It is estimated that ∼1% of European ancestry patients clinically diagnosed with type 1 diabetes (T1D) actually have monogenic forms of the disease. Because of the much lower incidence of true T1D in East Asians, we hypothesized that the percentage would be much higher. To test this, we sequenced the exome of 82 Chinese Han patients clinically diagnosed with T1D but negative for three autoantibodies. Analysis focused on established or proposed monogenic diabetes genes. We found credible mutations in 18 of the 82 autoantibody-negative patients (22%). All mutations had consensus pathogenicity support by five algorithms. As in Europeans, the most common gene was HNF1A (MODY3), in 6 of 18 cases. Surprisingly, almost as frequent were diallelic mutations in WFS1, known to cause Wolfram syndrome but also described in nonsyndromic cases. Fasting C-peptide varied widely and was not predictive. Given the 27.4% autoantibody negativity in Chinese and 22% mutation rate, we estimate that ∼6% of Chinese with a clinical T1D diagnosis have monogenic diabetes. Our findings support universal sequencing of autoantibody-negative cases as standard of care in East Asian patients with a clinical T1D diagnosis. Nonsyndromic diabetes with WSF1 mutations is not rare in Chinese. Its response to alternative treatments should be investigated.

Maternally Inherited Diabetes Mellitus Associated with a Novel m.15897G>A Mutation in Mitochondrial tRNAThr Gene

We report here the clinical, genetic, and molecular characteristics of type 2 diabetes in a Chinese family. There are differences in the severity and age of onset in diabetes among these families. By molecular analysis of the complete mitochondrial genome in this family, we identified the homoplasmic m.15897G>A mutation underwent sequence analysis of whole mitochondrial DNA genome, which localized at conventional position ten of tRNA^Thr, and distinct sets of mtDNA polymorphisms belonging to haplogroup D4b1. This mutation has been implicated to be important for tRNA identity and stability. Using cybrid cell models, the decreased efficiency of mitochondrial tRNA^Thr levels caused by the m.15897G>A mutation results in respiratory deficiency, protein synthesis and assembly, mitochondrial ATP synthesis, and mitochondrial membrane potential. These mitochondrial dysfunctions caused an increase in the production of reactive oxygen species in the mutant cell lines. These data provide a direct evidence that a novel tRNA mutation was associated with T2DM. Thus, our findings provide a new insight into the understanding of pathophysiology of maternally inherited diabetes.

Genomic profiling of mitochondrial DNA reveals novel complex gene mutations in familial type 2 diabetes mellitus individuals from Mizo ethnic population, Northeast India

The variants reported for mitochondrial DNA (mtDNA) and type 2 diabetes (T2D) may not be accountable for the disease in certain other populations and the risk depends upon numerous factors which may include genetics, environment as well as ethnicity. This leads to a challenge in identifying, exploring and comparing the variants between diabetic cases and healthy controls in a remote unexplored tribal population. To study the possible contribution of mtDNA variants, we sequenced the entire mitochondrial genomes and the frequencies of mtSNPs, their association with familial T2D and the potential impact of non-synonymous substitutions on protein functions were determined. The mtSNP 8584 G > A (ATP6: A20T) was detected in 14.28% of the diabetic patients and none in the control groups. The mitochondrial ND3 variant 10398A > G was found to be significantly associated with the risk of T2D (OR = 9.489, 95% CI = 1.161-77.54, P value = 0.036). A novel Frame-shift substitution ND5: 81_81ins A at position 12,417 was observed in 53.57% of diabetic individuals. Majority of the variants lie in tRNA-Phe in the non-protein coding region of mtDNA for both diabetic cases and common cases. We concluded that mutations in the coding (synonymous or non-synonymous) and noncoding regions of the mitochondria might have contribution towards the development of T2D. Our study is the first to report the distinct mitochondrial variants which may be attributed to the susceptibility as well as development of type 2 diabetes in an ethnic tribe from northeast India.

Dynamic derangement in amino acid profile during and after a stroke-like episode in adult-onset mitochondrial disease: a case report

Background

Maternally inherited diabetes and deafness, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes are examples of mitochondrial diseases that are relatively common in the adult population. Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes are assumed to be associated with decreases in arginine and citrulline. Biomarkers, such as growth differentiation factor-15, were developed to assist in the diagnosis of mitochondrial diseases.

Case presentation

A 55-year-old Japanese man, an insulin user, presented after a loss of consciousness. A laboratory test showed diabetic ketoacidosis. He and his mother had severe hearing difficulty. Bilateral lesions on magnetic resonance imaging, the presence of seizure, and an elevated ratio of lactate to pyruvate, altogether suggested a diagnosis of mitochondrial disease. Mitochondrial DNA in our patient’s peripheral blood was positive with a 3243A>G mutation, which is the most frequent cause of maternally inherited diabetes and deafness, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes. As a result, maternally inherited diabetes and deafness/mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes was diagnosed. We measured growth differentiation factor-15 and multiple amino acids in his blood, longitudinally during and after the stroke-like episode. Growth differentiation factor-15 was increased to an immeasurably high level on the day of the stroke-like episode. Although his diabetes improved with an increased dose of insulin, the growth differentiation factor-15 level gradually increased, suggesting that his mitochondrial insufficiency did not improve. Multiple amino acid species, including arginine, citrulline, and taurine, showed a decreased level on the day of the episode and a sharp increase the next day. In contrast, the level of aspartic acid increased to an extremely high level on the day of the episode, and decreased gradually thereafter.

Conclusions

Growth differentiation factor-15 can be used not only for the diagnosis of mitochondrial disease, but as an indicator of its acute exacerbation. A stroke-like episode of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes reflects a drastic derangement of multiple amino acids. The involvement of aspartic acid in the episodes should be explored in future studies.

Insights into pancreatic β cell energy metabolism using rodent β cell models

Background: Mitochondrial diabetes is primarily caused by β-cell failure, a cell type whose unique properties are important in pathogenesis. Methods: By reducing glucose, we induced energetic stress in two rodent β-cell models to assess effects on cellular function. Results: Culturing rat insulin-secreting INS-1 cells in low glucose conditions caused a rapid reduction in whole cell respiration, associated with elevated mitochondrial reactive oxygen species production, and an altered glucose-stimulated insulin secretion profile. Prolonged exposure to reduced glucose directly impaired mitochondrial function and reduced autophagy. Conclusions: Insulinoma cell lines have a very different bioenergetic profile to many other cell lines and provide a useful model of mechanisms affecting β-cell mitochondrial function.

Mitochondrial mutation m.3243A>G associates with insulin resistance in non-diabetic carriers

AIM

This case-control study aimed to examine impairments in glucose metabolism in non-diabetic carriers of the mitochondrial mutation m.3243A>G by evaluating insulin secretion capacity and sensitivity.

METHODS

Glucose metabolism was investigated in 23 non-diabetic m.3243A>G carriers and age-, sex- and BMI-matched healthy controls with an extended 4-h oral glucose tolerance test (OGTT). Insulin sensitivity index and acute insulin response were estimated on the basis of the OGTT. This was accompanied by examination of body composition by dual-energy X-ray absorptiometry (DXA), maximum aerobic capacity and a Recent Physical Activity Questionnaire (RPAQ).

RESULTS

Fasting p-glucose, s-insulin and s-c-peptide levels did not differ between m.3243A>G carriers and controls. Insulin sensitivity index (BIGTT-S1) was significantly lower in the m.3243A>G carriers, but there was no difference in the acute insulin response between groups. P-lactate levels were higher in carriers throughout the OGTT. VO2max, but not BMI, waist and hip circumferences, lean and fat body mass%, MET or grip strength, was lower in mutation carriers. BIGTT-S1 remained lower in mutation carriers after adjustment for multiple confounding factors including VO2max in regression analyses.

CONCLUSIONS

Glucose metabolism in m.3243A>G carriers was characterized by reduced insulin sensitivity, which could represent the earliest phase in the pathogenesis of m.3243A>G-associated diabetes.

Cardiovascular Manifestations of Mitochondrial Disease

Genetic mitochondrial cardiomyopathies are uncommon causes of heart failure that may not be seen by most physicians. However, the prevalence of mitochondrial DNA mutations and somatic mutations affecting mitochondrial function are more common than previously thought. In this review, the pathogenesis of genetic mitochondrial disorders causing cardiovascular disease is reviewed. Treatment options are presently limited to mostly symptomatic support, but preclinical research is starting to reveal novel approaches that may lead to better and more targeted therapies in the future. With better understanding and clinician education, we hope to improve clinician recognition and diagnosis of these rare disorders in order to improve ongoing care of patients with these diseases and advance research towards discovering new therapeutic strategies to help treat these diseases.

The tRNA Epitranscriptome and Diabetes: Emergence of tRNA Hypomodifications as a Cause of Pancreatic β-Cell Failure

tRNAs are crucial noncoding RNA molecules that serve as amino acid carriers during protein synthesis. The transcription of tRNA genes is a highly regulated process. The tRNA pool is tissue and cell specific, it varies during development, and it is modulated by the environment. tRNAs are highly posttranscriptionally modified by specific tRNA-modifying enzymes. The tRNA modification signature of a cell determines the tRNA epitranscriptome. Perturbations in the tRNA epitranscriptome, as a consequence of mutations in tRNAs and tRNA-modifying enzymes or environmental exposure, have been associated with human disease, including diabetes. tRNA fragmentation induced by impaired tRNA modifications or dietary factors has been linked to pancreatic β-cell demise and paternal inheritance of metabolic traits. Herein, we review recent findings that associate tRNA epitranscriptome perturbations with diabetes.

How the most common mitochondrial DNA mutation (m.3243A>G) vanishes from leukocytes: a mathematical model

Mitochondrial diseases may be caused by alterations of the mitochondrial genome. The pathogenic variant m.3243A>G is one of the most frequent causes of mitochondrial disease and the most common mitochondrial DNA mutation. Patients with a variant in mitochondrial DNA can have a mixture of mutated and wild-type genomes (heteroplasmy). In the case of the pathogenic variant m.3243A>G, the degree of heteroplasmy (H) correlates to some extent with the severity of the disease. Several longitudinal studies, where H is measured at two different time-points, have shown an annual decline in leukocyte H values. Thus far, only an exponential decay of H with time has been noted but a mechanistic model is lacking. Here, I describe a deterministic mathematical model that accounts for the decline of H in leukocytes based on selective mechanisms acting at the stem cell level. The 'inverted-sigmoid' model provides estimates of at-birth H levels closer to those observed in post-mitotic tissues, such as skeletal muscle, than the estimates provided by an exponential decay. The new model never leads to predictions of H > 100% and provides a stronger correlation between at-birth H values in leukocytes and the scores of the Newcastle Mitochondrial Disease Scale for Adults, which can be of practical utility. This model could be extended to other mitochondrial DNA disease-causing variants.

Wound exudate CXCL6: a potential biomarker for wound healing of diabetic foot ulcers

AIM

The aim of this study was to investigate the relationship between CXCL-6 levels in wound exudates and healing of diabetic foot ulcers (DFU).

MATERIALS & METHODS

One hundred patients with neuropathic DFU were recruited. Wound exudate CXCL-6 levels were measured by enzyme-linked immunosorbent assay. Patients were followed for 24 weeks and divided into rapidly healing and nonhealing groups.

RESULTS

Compared with the NH group, the mean CXCL-6 levels in the wound exudates of the rapidly healing group were significantly higher. After adjusting for traditional risk factors, wound exudate CXCL-6 levels were still significantly associated with wound healing.

CONCLUSION

CXCL6 is an independent predictor of wound healing in DFU patients and may be a potentially novel therapeutic target for the treatment of DFU.

De Novo Mutation of m.3243A>G together with m.16093T>C Associated with Atypical Clinical Features in a Pedigree with MIDD Syndrome

BACKGROUND

The syndrome of maternally inherited diabetes and deafness (MIDD) is typically caused by the m.3243A>G mutation and widely considered maternally inherited. In our study, we aimed to investigate the heredity way of the m.3243A>G among pedigrees with MIDD and discover novel mitochondrial DNA mutations related to atypical clinical phenotypes.

METHODS

Heteroplasmy levels of the m.3243A>G mutation in peripheral blood, saliva, and urine sediment of 31 individuals from 10 unrelated pedigrees were measured by pyrosequencing. Clinical evaluations including endocrinological, audiological, and magnetic resonance imaging (MRI) examinations, mitochondrial function evaluation in peripheral blood mononuclear cells (PBMCs), and whole mitochondrial DNA (mtDNA) sequencing were performed among the spontaneous mutant pedigrees.

RESULTS

Among the 10 unrelated MIDD pedigrees, we found that the de novo m.3243A>G mutation occurred in the family 1957 (F1957). The proband (F1957-II-1) and her son (F1957-III-1) both manifested diabetes with mild bilateral sensorineural hearing loss (SNHL) and abnormal brain MRI, and F1957-III-1 also complained of severe nausea and vomiting. Mitochondrial function evaluation in PBMCs revealed an increased level of ROS generation and decreased levels of ATP and mitochondrial membrane potential (ΔΨm) in the two m.3243A>G carriers. Whole mtDNA sequencing also revealed a de novo heteroplasmic substitution at m.16093T>C in both the proband and her son.

CONCLUSIONS

Our study showed that de novo m.3243A>G mutation accompanied by other point mutations may occur in the very early embryonic or germ cell stage without maternal inheritance, bringing about both typical and atypical clinical features.

Mitochondrial disease: an uncommon but important cause of diabetes mellitus

Mitochondrial diseases are rare, heterogeneous conditions affecting organs dependent on high aerobic metabolism. Presenting symptoms and signs vary depending on the mutation and mutant protein load. Diabetes mellitus is the most common endocrinopathy, and recognition of these patients is important due to its impact on management and screening of family members. In particular, glycemic management differs in these patients: the use of metformin is avoided because of the risk of lactic acidosis. We describe a patient who presented with gradual weight loss and an acute presentation of hyperglycemia complicated by the superior mesenteric artery syndrome. His maternal history of diabetes and deafness and a personal history of hearing impairment led to the diagnosis of a mitochondrial disorder. Learning points: •• The constellation of diabetes, multi-organ involvement and maternal inheritance should prompt consideration of a mitochondrial disorder. •• Mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS) and maternally inherited diabetes and deafness (MIDD) are the most common mitochondrial diabetes disorders caused by a mutation in m.3243A>G in 80% of cases. •• Metformin should be avoided due to the risk of lactic acidosis. •• There is more rapid progression to insulin therapy and higher prevalence of diabetic complications compared to type 2 diabetes. •• Diagnosis of a mitochondrial disorder leads to family screening, education and surveillance for future complications. •• Superior mesenteric artery syndrome, an uncommon but important cause of intestinal pseudo-obstruction in cases of significant weight loss, has been reported in MELAS patients.

Monogenic Diabetes in Children and Adolescents: Recognition and Treatment Options

PURPOSE OF REVIEW

We provide a review of monogenic diabetes in young children and adolescents with a focus on recognition, management, and pharmacological treatment.

RECENT FINDINGS

Monogenic forms of diabetes account for approximately 1-2% of diabetes in children and adolescents, and its incidence has increased in recent years due to greater awareness and wider availability of genetic testing. Monogenic diabetes is due to single gene defects that primarily affect beta cell function with more than 30 different genes reported. Children with antibody-negative, C-peptide-positive diabetes should be evaluated and genetically tested for monogenic diabetes. Accurate genetic diagnosis impacts treatment in the most common types of monogenic diabetes, including the use of sulfonylureas in place of insulin or other glucose-lowering agents or discontinuing pharmacologic treatment altogether. Diagnosis of monogenic diabetes can significantly improve patient care by enabling prediction of the disease course and guiding appropriate management and treatment.

Not quite type 1 or type 2, what now? Review of monogenic, mitochondrial, and syndromic diabetes

Diabetes mellitus is a heterogeneous group of conditions defined by resultant chronic hyperglycemia. Given the increasing prevalence of diabetes mellitus and the increasing understanding of genetic etiologies, we present a broad review of rare genetic forms of diabetes that have differing diagnostic and/or treatment implications from type 1 and type 2 diabetes. Advances in understanding the genotype-phenotype associations in these rare forms of diabetes offer clinically available examples of evolving precision medicine where defining the correct genetic etiology can radically alter treatment approaches. In this review, we focus on forms of monogenic diabetes, mitochondrial diabetes, and syndromic diabetes.

CHORIOCAPILLARIS SIGNAL VOIDS IN MATERNALLY INHERITED DIABETES AND DEAFNESS AND IN PSEUDOXANTHOMA ELASTICUM

PURPOSE

To evaluate the pattern of choriocapillaris signal voids in maternally inherited diabetes and deafness and in pseudoxanthoma elasticum in eyes before the development of any geographic atrophy.

METHODS

The choriocapillaris under the central macula was imaged with the Optovue RTVue XR Avanti using a 10 μm slab thickness. Automatic local thresholding of the resultant raw data extracted areas of absent flow signal, called signal voids, and these were counted and logarithmically binned. The signal void patterns were analyzed in four eyes of two patients with maternally inherited diabetes and deafness and four eyes of three patients with pseudoxanthoma elasticum. None of the patients had geographic atrophy. These data were compared with 55 eyes of 38 healthy control subjects and analyzed with generalized estimating equations.

RESULTS

The choriocapillaris images in maternally inherited diabetes and deafness and pseudoxanthoma elasticum show that the model of signal voids followed a power law distribution, but with a slope and offset much lower than the normal control group, adjusted for age (P < 0.001). The eyes in the disease group were much more likely to have signal voids greater than 40,000 μm.

CONCLUSION

Before the development of any overt geographic atrophy, patients with maternally inherited diabetes and deafness and pseudoxanthoma elasticum show pronounced abnormalities of choriocapillaris flow. Current clinical measures of retinal pigment epithelial health only look for areas of cell death, as in geographic atrophy. It is not possible to determine from current imaging if the choriocapillaris loss precedes potential loss of function of the retinal pigment epithelium, such as secretion of vascular endothelial growth factor.

Patients With Mitochondrial Disease Have an Inadequate Nutritional Intake

BACKGROUND

Mitochondrial disease (MD) is a group of disorders caused by dysfunctional mitochondria, the organelles that generate energy for the cell. Malnutrition in patients with MD may lead to increased mitochondrial dysfunction, which may enhance already existing symptoms. The aim of this study was to investigate whether patients with MD have an insufficient or unbalanced food intake and to establish which nutrients and product groups are particularly compromised in this patient group.

METHODS

In this observational, cross-sectional, retrospective study, sixty 3-day nutrition diaries of adult patients with MD were analyzed and compared with the Dutch recommended daily allowance and the Dutch National Food Consumption Survey (DNFCS).

RESULTS

The intake of all macronutrients and micronutrients of patients with MD was significantly different from Dutch recommended daily allowance values with the exception of fat and iron. In particular, protein and calcium intake in patients with MD was significantly lower when compared with the DNFCS. Interindividual differences were high. Also, intake of fiber, sugars, saturated fat, and vitamin D differed from recommendations for the overall population. In comparison with DNFCS, the intake of dairy products and drinks was significant lower in patients.

CONCLUSIONS

Our study demonstrates that many patients with MD have an inadequate diet. Specifically, intake of protein, calcium, dairy products, and fluids were low. Overall, eating a healthy diet seems as difficult for patients with MD as for the general population. Since interindividual differences are high, individual diet counseling is recommended for all adult patients with MD.

Heterozygous RFX6 protein truncating variants are associated with MODY with reduced penetrance

Finding new causes of monogenic diabetes helps understand glycaemic regulation in humans. To find novel genetic causes of maturity-onset diabetes of the young (MODY), we sequenced MODY cases with unknown aetiology and compared variant frequencies to large public databases. From 36 European patients, we identify two probands with novel RFX6 heterozygous nonsense variants. RFX6 protein truncating variants are enriched in the MODY discovery cohort compared to the European control population within ExAC (odds ratio = 131, P = 1 × 10-4). We find similar results in non-Finnish European (n = 348, odds ratio = 43, P = 5 × 10-5) and Finnish (n = 80, odds ratio = 22, P = 1 × 10-6) replication cohorts. RFX6 heterozygotes have reduced penetrance of diabetes compared to common HNF1A and HNF4A-MODY mutations (27, 70 and 55% at 25 years of age, respectively). The hyperglycaemia results from beta-cell dysfunction and is associated with lower fasting and stimulated gastric inhibitory polypeptide (GIP) levels. Our study demonstrates that heterozygous RFX6 protein truncating variants are associated with MODY with reduced penetrance.Maturity-onset diabetes of the young (MODY) is the most common subtype of familial diabetes. Here, Patel et al. use targeted DNA sequencing of MODY patients and large-scale publically available data to show that RFX6 heterozygous protein truncating variants cause reduced penetrance MODY.

Insights into pancreatic β cell energy metabolism using rodent β cell models

Background: Mitochondrial diabetes is primarily caused by β-cell failure, a cell type whose unique properties are important in pathogenesis. Methods: By reducing glucose, we induced energetic stress in two rodent β-cell models to assess effects on cellular function. Results: Culturing rat insulin-secreting INS-1 cells in low glucose conditions caused a rapid reduction in whole cell respiration, associated with elevated mitochondrial reactive oxygen species production, and an altered glucose-stimulated insulin secretion profile. Prolonged exposure to reduced glucose directly impaired mitochondrial function and reduced autophagy. Conclusions: Insulinoma cell lines have a very different bioenergetic profile to many other cell lines and provide a useful model of mechanisms affecting β-cell mitochondrial function.

RETINAL VEIN OCCLUSION IN A PATIENT WITH MATERNALLY INHERITED DIABETES AND DEAFNESS

PURPOSE

To report a case of maternally inherited diabetes and deafness complicated by branch retinal vein occlusion and cystoid macular edema.

METHODS

Retrospective case report. Multimodal imaging including spectral domain optical coherence tomography, en face optical coherence tomography, and fundus autofluorescence was preformed, and the findings are presented.

FINDINGS

A 58-year-old female with a history of diabetes mellitus, hearing loss, and a previous diagnosis of age-related macular degeneration presented with decreased vision in the right eye. Clinical examination and multimodal imaging demonstrated a right inferior branch retinal vein occlusion complicated by cystoid macular edema and bilateral maculopathy suspicious for maternally inherited diabetes and deafness. Genetic testing confirmed an A3243G mitochondrial mutation.

CONCLUSION

Multimodal retinal imaging is a key to guide diagnosis of rare genetic diseases such as maternally inherited diabetes and deafness. We report the unusual presentation of maternally inherited diabetes and deafness complicated by branch retinal vein occlusion and cystoid macular edema.

Insights into pancreatic β cell energy metabolism using rodent β cell models

Background:Mitochondrial diabetes is primarily caused by β-cell failure, but there are gaps in our understanding of pathogenesis.Methods:By reducing glucose, we induced energetic stress in two rodent β-cell models to assess effects on cellular function.Results:Culturing rat insulin-secreting INS-1 cells in low glucose conditions caused a rapid reduction in whole cell respiration, associated with elevated mitochondrial reactive oxygen species production, and an altered glucose-stimulated insulin secretion profile. Prolonged exposure to reduced glucose directly impaired mitochondrial function and reduced autophagy.Conclusions:Insulinoma cell lines provide a useful model of mechanisms affecting β-cell mitochondrial function or studying mitochondrial associated drug toxicity.

Mitochondrial disease and endocrine dysfunction

Mitochondria are critical organelles for endocrine health; steroid hormone biosynthesis occurs in these organelles and they provide energy in the form of ATP for hormone production and trafficking. Mitochondrial diseases are multisystem disorders that feature defective oxidative phosphorylation, and are characterized by enormous clinical, biochemical and genetic heterogeneity. To date, mitochondrial diseases have been found to result from >250 monogenic defects encoded across two genomes: the nuclear genome and the ancient circular mitochondrial genome located within mitochondria themselves. Endocrine dysfunction is often observed in genetic mitochondrial diseases and reflects decreased intracellular production or extracellular secretion of hormones. Diabetes mellitus is the most frequently described endocrine disturbance in patients with inherited mitochondrial diseases, but other endocrine manifestations in these patients can include growth hormone deficiency, hypogonadism, adrenal dysfunction, hypoparathyroidism and thyroid disease. Although mitochondrial endocrine dysfunction frequently occurs in the context of multisystem disease, some mitochondrial disorders are characterized by isolated endocrine involvement. Furthermore, additional monogenic mitochondrial endocrine diseases are anticipated to be revealed by the application of genome-wide next-generation sequencing approaches in the future. Understanding the mitochondrial basis of endocrine disturbance is key to developing innovative therapies for patients with mitochondrial diseases.

Rapid Detection of the mt3243A > G Mutation Using Urine Sediment in Elderly Chinese Type 2 Diabetic Patients

OBJECTIVE

In this study, we aimed to identify mt3243A > G mutation carriers in a group of Chinese elderly type 2 diabetic patients by a rapid and noninvasive diagnostic system.

METHODS

DNA was extracted from blood, saliva, and urine sediment samples. The mutation screening and quantitation of heteroplasmy were performed by high-resolution melting (HRM) curve and pyrosequencing, respectively. Patients with mt3243A > G mutation underwent a detailed audiometric, ophthalmologic, neurological, and cardiac examination.

RESULTS

Two patients (2/1041) carrying the mt3243A > G mutation were detected among all type 2 diabetic patients. In patient 1, the heteroplasmy was 0.8%, 2.8%, and 14.7% in peripheral blood leukocytes, saliva, and urine sediment, respectively. In patient 2, the heteroplasmy was 5.3%, 8.4%, and 37.7% in peripheral blood leukocytes, saliva, and urine sediment, respectively. Both of the two patients showed hearing impairment. Abnormal ophthalmologic conditions and hyperintensity on T2-weighted magnetic resonance images were showed in patient 1.

CONCLUSION

The occurrence of mt3243 A > G mutation was 0.2% in Chinese elderly type 2 diabetic patients. Moreover, detection of mt3243 A > G mutation in urine sediment with high-resolution melting (HRM) curve and pyrosequencing is feasible in molecular genetic diagnosis.

A preliminary study to evaluate the strategy of combining clinical criteria and next generation sequencing (NGS) for the identification of monogenic diabetes among multi-ethnic Asians

AIMS

Diabetes is increasing globally and Asia is the epicenter. Among those with young-onset diabetes (<45years), the prevalence of monogenic diabetes is estimated to be non-trivial (∼5%). An accurate diagnosis of monogenic diabetes is important to inform treatment, prognosis and genetic counseling. Therefore, a robust clinical algorithm to identify probands for testing is needed. Our aims are (1) to select probands for genetic testing and variant identification based on their clinical phenotype and (2) to evaluate the MODY probability calculator in our multi-ethnic Asian population.

METHODS

Eighty-four potential probands, identified in accordance with clinical practice guidelines, were subjected to re-sequencing of 16 monogenic diabetes genes and targeted genotyping for mitochondrial 3243A>G point-mutation. Variants, confirmed by bi-directional Sanger sequencing, were classified as pathogenic if they fulfilled the criteria adapted from American College of Medical Genetics. Performance of MODY calculator (with positive-predictive threshold set at >62.4%) for those with diabetes-onset ⩽35years (data input-limit) (n=71) was also evaluated.

RESULTS

Thirteen subjects (15.5%) harbored likely pathogenic/pathogenic variants: 6 (2 novel) in HNF1A (1 subject concomitantly had another HNF4A variant), 1 in HNF4A, 2 in mt3243A>G and 1 each in GCK, KCNJ11 (novel), ABCC8 (novel) and PAX4 (novel). Performance of the MODY calculator was: sensitivity 0.769, specificity 0.603 and negative predictive value 0.921. When analysis was restricted to MODY1-3, the performance was: 0.875, 0.587 and 0.974, respectively.

CONCLUSIONS

The prevalence of MODY is non-trivial (∼15%) among Asians with young-onset diabetes. MODY calculator performs well in our population in nominating probands for genetic testing.

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.

Treating young adults with type 2 diabetes or monogenic diabetes

It is increasingly recognised that diabetes in young adults has a wide differential diagnosis. There are many monogenic causes, including monogenic beta-cell dysfunction, mitochondrial diabetes and severe insulin resistance. Type 2 diabetes in the young is becoming more prevalent, particularly after adolescence. It's important to understand the clinical features and diagnostic tools available to classify the different forms of young adult diabetes. Classic type 1 diabetes is characterised by positive β-cell antibodies and absence of endogenous insulin secretion. Young type 2 diabetes is accompanied by metabolic syndrome with obesity, hypertension and dyslipidaemia. Monogenic β-cell dysfunction is characterised by non-autoimmune, C-peptide positive diabetes with a strong family history, while mitochondrial diabetes features deafness and other neurological involvement. Severe insulin resistance involves a young-onset metabolic syndrome often with a disproportionately low BMI. A suspected diagnosis of monogenic diabetes is confirmed with genetic testing, which is widely available in specialist centres across the world. Treatment of young adult diabetes is similarly diverse. Mutations in the transcription factors HNF1A and HNF4A and in the β-cell potassium ATP channel components cause diabetes which responds to low dose and high dose sulfonylurea agents, respectively, while glucokinase mutations require no treatment. Monogenic insulin resistance and young-onset type 2 diabetes are both challenging to treat, but first line management involves insulin sensitisers and aggressive management of cardiovascular risk. Outcomes are poor in young-onset type 2 diabetes compared to both older onset type 2 and type 1 diabetes diagnosed at a similar age. The evidence base for treatments in monogenic and young-onset type 2 diabetes relies on studies of moderate quality at best and largely on extrapolation from work conducted in older type 2 diabetes subjects. Better quality, larger studies, particularly of newer agents would improve treatment prospects for young adults with diabetes.