Penetrance and expressivity of mitochondrial variants in a large clinically unselected population

Whole genome sequencing (WGS) from large clinically unselected cohorts provides a unique opportunity to assess the penetrance and expressivity of rare and/or known pathogenic mitochondrial variants in population. Using WGS from 179 862 clinically unselected individuals from the UK Biobank, we performed extensive single and rare variant aggregation association analyses of 15 881 mtDNA variants and 73 known pathogenic variants with 15 mitochondrial disease-relevant phenotypes. We identified 12 homoplasmic and one heteroplasmic variant (m.3243A>G) with genome-wide significant associations in our clinically unselected cohort. Heteroplasmic m.3243A>G (MAF = 0.0002, a known pathogenic variant) was associated with diabetes, deafness and heart failure and 12 homoplasmic variants increased aspartate aminotransferase levels including three low-frequency variants (MAF ~0.002 and beta~0.3 SD). Most pathogenic mitochondrial disease variants (n = 66/74) were rare in the population (<1:9000). Aggregated or single variant analysis of pathogenic variants showed low penetrance in unselected settings for the relevant phenotypes, except m.3243A>G. Multi-system disease risk and penetrance of diabetes, deafness and heart failure greatly increased with m.3243A>G level ≥ 10%. The odds ratio of these traits increased from 5.61, 12.3 and 10.1 to 25.1, 55.0 and 39.5, respectively. Diabetes risk with m.3243A>G was further influenced by type 2 diabetes genetic risk. Our study of mitochondrial variation in a large-unselected population identified novel associations and demonstrated that pathogenic mitochondrial variants have lower penetrance in clinically unselected settings. m.3243A>G was an exception at higher heteroplasmy showing a significant impact on health making it a good candidate for incidental reporting.

Identification of eight genomic protective alleles for mitochondrial diabetes by Kinship-graph convolutional network

AIMS

Nearly 85% of maternally inherited diabetes and deafness (MIDD) are caused by the m.3243A>G mutation in the mitochondrial DNA. However, the clinical phenotypes of MIDD may also be influenced by the nuclear genome, this study aimed to investigate nuclear genome variants that influence clinical phenotypes associated with m.3243A>G mutation in MIDD based on whole-genome sequencing of the patients belonging to pedigrees.

MATERIALS AND METHODS

We analyzed a whole-genome sequencing (WGS) dataset from blood samples of 38 MIDD patients with the m.3243A > G mutation belonging to 10 pedigrees, by developing a Kinship-graph convolutional network approach, called Ki-GCN, integrated with the conventional genome-wide association study (GWAS) methods.

RESULTS

We identified eight protective alleles in the nuclear genome that have protective effects against the onset of MIDD, related deafness, and also type 2 diabetes. Based on these eight protective alleles, we constructed an effective logistic regression model to predict the early or late onset of MIDD patients.

CONCLUSIONS

There are protective alleles in the nuclear genome that are associated with the onset-age of MIDD patients and might also provide protective effects on the deafness derived from MIDD patients.

Imeglimin-mediated glycemic control in maternally inherited deafness and diabetes

Mitochondrial dysfunction causes maternally inherited deafness and diabetes (MIDD). Herein, we report improved glycemic control in a 47-year-old Japanese woman with MIDD using imeglimin without major adverse effects. Biochemical tests and metabolome analysis were performed before and after imeglimin administration. Blood glucose level fluctuations were determined. Sulfonylureas, dipeptidyl peptidase-4 inhibitors (DPP4is), and sodium glucose transporter-2 inhibitors (SGLT2i) were administered to evaluate the efficacy of their combination with imeglimin. Imeglimin decreased the HbA1c and ammonia levels and increased the time-in-range, C-peptide reactivity, and glucagon level. Elevated citrulline and histamine levels were decreased by imeglimin. The hypoglycemic effect was not enhanced by imeglimin when combined with sulfonylurea or DPP4i, but the blood glucose level was improved when combined with SGLT2i. Imeglimin improved glucose concentration-dependent insulin secretion and maximized the insulin secretory capacity by improving mitochondrial function and glutamine metabolism and urea circuit abnormalities by promoting glucagon secretion. Imeglimin could improve glycemic control in MIDD.

Imeglimin-mediated glycemic control in maternally inherited deafness and diabetes

Mitochondrial dysfunction causes maternally inherited deafness and diabetes (MIDD). Herein, we report improved glycemic control in a 47-year-old Japanese woman with MIDD using imeglimin without major adverse effects. Biochemical tests and metabolome analysis were performed before and after imeglimin administration. Blood glucose level fluctuations were determined. Sulfonylureas, dipeptidyl peptidase-4 inhibitors (DPP4is), and sodium glucose transporter-2 inhibitors (SGLT2i) were administered to evaluate the efficacy of their combination with imeglimin. Imeglimin decreased the HbA1c and ammonia levels and increased the time-in-range, C-peptide reactivity, and glucagon level. Elevated citrulline and histamine levels were decreased by imeglimin. The hypoglycemic effect was not enhanced by imeglimin when combined with sulfonylurea or DPP4i, but the blood glucose level was improved when combined with SGLT2i. Imeglimin improved glucose concentration-dependent insulin secretion and maximized the insulin secretory capacity by improving mitochondrial function and glutamine metabolism and urea circuit abnormalities by promoting glucagon secretion. Imeglimin could improve glycemic control in MIDD.

Successful transcatheter mitral valve repair for functional mitral regurgitation in a patient with mitochondrial cardiomyopathy: a case report

Background

Mitochondrial diseases are a group of genetic disorders caused by nuclear or mitochondrial DNA gene mutations and characterized by multiorgan disorders, including cardiomyopathy. Mitochondrial cardiomyopathy is occasionally complicated by hypertrophic cardiomyopathy with/without left ventricular systolic dysfunction, dilated cardiomyopathy, and left ventricular non-compaction. In such cases, the dilated left ventricle impairs coaptation of the mitral leaflets and leads to functional mitral regurgitation. To date, valvular interventions in patients with mitochondrial cardiopathy have not been investigated.

Case summary

A 64-year-old woman with mitochondrial cardiopathy was referred to our hospital owing to dyspnoea. She experienced her first admission with heart failure at age 60 years. At 62 years old, she was diagnosed with maternally inherited diabetes and deafness with mitochondrial cardiomyopathy based on mitochondrial DNA sequencing. Despite administration of guideline-directed medical therapy and high-dose taurine supplementation, she was repeatedly hospitalized for heart failure. At admission, transthoracic echocardiography revealed severe functional mitral regurgitation due to left ventricular dilatation. Surgical risk was considered high (Society of Thoracic Surgeons score of 12.6%); therefore, transcatheter edge-to-edge repair with the MitraClip system was performed. Two devices deployed at the middle segment of the anterior and posterior leaflet successfully reduced mitral regurgitation. The patient was free from cardiovascular events during the 2-year follow-up period.

Discussion

Transcatheter edge-to-edge repair is a less invasive and effective treatment for severe drug-refractory mitral regurgitation in patients with mitochondrial disease. Given the limited therapeutic options for mitochondrial cardiopathy, further studies are required to uncover the mechanism underlying mitochondrial diseases and establish disease-specific treatments.

Cerebellar vermis hypoplasia and bilateral basal ganglia calcification in maternally inherited diabetes and deafness

Maternally inherited diabetes and deafness (MIDD) is a rare diabetic syndrome mainly caused by a point mutation in the mitochondrial DNA. It affects up to 1% of patients with diabetes but is often unrecognized by physicians. We report a case of MIDD in a 29-year-old man with coexisting imaging of cerebellar vermis hypoplasia and bilateral basal ganglia calcification.

Pilot Trial on the Effect of 5-Aminolevulinic Acid on Glucose Tolerance in Patients with Maternally Inherited Diabetes and Deafness

INTRODUCTION

The amino acid 5-aminolevulinic acid (5-ALA) is the first heme biosynthetic precursor. The combination of 5-ALA with sodium ferrous citrate (SFC) enhances heme production, leading to increased adenosine triphosphate (ATP) production in mitochondria. We investigated whether administering 5-ALA/SFC improves glucose tolerance with an increase in insulin secretion in patients with maternally inherited diabetes and deafness (MIDD), which is characterized by an insulin secretory disorder due to impaired mitochondrial ATP production.

METHODS

This was a single-arm, open-label, interventional study. We prospectively administered the oral glucose tolerance test (OGTT) twice in five patients with MIDD who had received intensive insulin therapy: before and 24 weeks after an administration of 5-ALA/SFC (200/232 mg per day). We measured the concentrations of glucose, insulin, C-peptide, and proinsulin at fasting, and 30, 60, and 120 min after glucose load in each OGTT. The primary endpoint was the changes in the area under the curve (AUC) of serum insulin from 0 to 120 min during OGTT from baseline to 24 weeks.

RESULTS

The serum insulin AUC (µU/mL) during the 120-min OGTT tended to increase from baseline to 24 weeks but not significantly (17.1 ± 13.7 versus 22.3 ± 13.4, p = 0.077). The plasma glucose AUC (mg/dL) during the 120-min OGTT at 24 weeks was not significantly decreased; the late phase of glucose excursion from 60 to 120 min was significantly decreased compared with baseline (357 ± 42 versus 391 ± 50, p = 0.041). The mean level of glycated hemoglobin (HbA1c) decreased from 8.3 ± 1.2% at baseline to 7.9 ± 0.3% at 24 weeks (p = 0.36) without increasing the daily dose of insulin injections.

CONCLUSION

The 24-week administration of 5-ALA/SFC did not demonstrate a significant improvement in insulin secretion in patients with MIDD. Further investigations with a larger number of patients and a placebo control group are required to clarify the potential efficacy of 5-ALA/SFC for ameliorating mitochondrial dysfunctions in MIDD.

TRIAL REGISTRATION

UMIN-CTR000040581 and jRCT071200025.

Maternally inherited diabetes and deafness coexists with lipoprotein lipase gene mutation-associated severe hyperlipidemia that was resistant to fenofibrate and atorvastatin, but sensitive to bezafibrate: A case report

Maternally inherited diabetes and deafness is a rare genetic disease mainly caused by a point mutation in mitochondrial deoxyribonucleic acid. Lipoprotein lipase gene mutations are associated with familial dyslipidemias, which are difficult to manage. We reported for the first time a case that had both maternally inherited diabetes and severe hyperlipidemia caused by lipoprotein lipase gene mutation (C.347(exon3)G>C) that was resistant to fenofibrate and atorvastatin. We were able to manage the patient’s hyperlipidemia with bezafibrate, and her diabetes was well controlled with insulin. In conclusion, genetic testing is helpful in identifying rare and interesting cases when clinicians suspect inheritable diseases. Additionally, when one fibrate drug is ineffective in treating hyperlipidemia, it might be worthwhile trying another fibrate.

Outer retinal tubulation and inner retinal pseudocysts in a patient with maternally inherited diabetes and deafness evaluated with optical coherence tomography angiogram

A 47-year-old lady (index case) with diabetes and deafness showed multiple oval circumferential areas of perifoveal atrophy in both eyes. Autofluorescence revealed areas of hypoautofluorescence. Optical coherence tomography (OCT) showed depression of inner retinal surface, inner retinal hyporeflective spaces (pseudocysts), disorganization/thinning of outer retina, outer retinal tubulation, loss of external limiting membrane, ellipsoid and interdigitation zone, and thinning of the retinal pigment epithelium and choriocapillaris. The patient was evaluated using OCT angiogram. Retinal lesions of her mother (68-year-old) were very obvious on autofluorescence imaging. The result of A3243G mutation in MTTL1 gene was positive in the index case confirming the diagnosis of maternally inherited diabetes and deafness (MIDD).

Chronic kidney disease caused by maternally inherited diabetes and deafness: a case report

Maternally inherited diabetes and deafness (MIDD) is a mitochondrial genetic disorder with variable clinical presentations, which can delay its diagnosis. Herein, we report the case of a 57-year-old Japanese man with MIDD who developed chronic kidney disease. He developed proteinuria long before his diabetes and deafness; at the age of 36 years, a renal biopsy showed minor glomerular abnormality and electron microscopy showed mild mitochondrial degeneration in the distal tubular epithelial cells. Twenty years later, a second renal biopsy showed nephrosclerosis with interstitial fibrosis and arteriolar hyaline thickening, despite the absence of hypertension and relatively good glycemic control. Granular swollen epithelial cells were found in the medullary collecting duct epithelium. Electron microscopy showed accumulating mitochondria in podocytes and tubular cells, leading to the diagnosis of MIDD. A muscle biopsy also showed ragged-red fibers, despite the absence of muscle weakness. Mitochondrial DNA analysis revealed an m.3243A > G mutation, and taurine supplementation was initiated. Our findings suggest that mitochondrial dysfunction is mainly associated with progressive renal damage.

Outer retinal tubulations in maternally inherited diabetes & deafness - associated macular dystrophy: case report

PURPOSE

To describe the presence of outer retinal tubulations (ORTs) in a patient diagnosed with maternally inherited diabetes and deafness (MIDD) - associated macular dystrophy.

METHODS

The patient underwent clinical examination assessing best-corrected visual acuity (BCVA), anterior segment evaluation and fundoscopy followed by optical coherence tomography (OCT). Audiological evaluation was also performed for the accurate diagnosis of MIDD.

RESULTS

A 57-year-old diabetic patient with mildly affected BCVA, macular dystrophy and severe neurosensory hearing loss was diagnosed with MIDD. Examination with OCT revealed the central loss of photoreceptors and the presence of ORTs in close proximity to the fovea. Regular follow-up seven months after her initial visit showed no alterations in the clinical and imaging status of the patient. In the context of family screening, the patient's sister presented with the diagnosis of pre-diabetes and a moderate sensorineural hearing loss, while fundus examination and OCT revealed no significant pathology. In this report, we present ORTs in association with MIDD.

CONCLUSIONS

ORTs are a non-specific finding that can be found in MIDD and other retinal dystrophies. Taking under consideration the rarity and the difficulty in diagnosing this entity, our data could serve as an addition to the existing knowledge in terms of clinical and imaging manifestations of MIDD.

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.

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.

Maternally inherited diabetes and deafness complicated by mesangial galactose-deficient IgA1 deposits: a case report

Background

Maternally inherited diabetes and deafness (MIDD), a mitochondrial genetic disorder, typically affects the kidneys and results in end-stage renal disease. Early diagnosis of MIDD is challenging when renal manifestations precede other key clinical features such as diabetes and deafness and/or when the disease is complicated by other renal pathologies.

Case presentation

Here, we present the case of a 33-year-old Japanese woman who had initially been diagnosed with IgA nephropathy but was found to have MIDD 6 years later. Two renal biopsies were conducted six years apart. While assessment of the first biopsy specimen with the monoclonal antibody (KM55) revealed mesangial IgA deposits (containing the galactose-deficient IgA1 variant [Gd-IgA1]), examination of the second specimen showed no mesangial IgA deposits and newly-developed glomerular global scleroses and tubular damage. Granular swollen epithelial cells (GSECs), characterised by abnormal mitochondria, were observed among the tubules and collecting ducts in both biopsy specimens. Mitochondrial DNA analysis revealed an m.3243A > G mutation.

Conclusions

We rediscovered the usefulness of GSECs as a pathologically distinctive feature of mitochondrial nephropathy and reviewed the literature regarding MIDD complicated by mesangial IgA deposition. Furthermore, we demonstrate that the mesangial IgA deposits in this patient consisted of the galactose-deficient IgA1 variant. The monoclonal antibody (KM55) might be a useful tool to distinguish IgAN from latent IgA deposits.

The clinical characteristics of patients with mitochondrial tRNA Leu(UUR)m.3243A > G mutation: Compared with type 1 diabetes and early onset type 2 diabetes

OBJECTIVE

This study presents nine patients with mitochondrial tRNA Leu (UUR) m.3243A>G mutation and compares the clinical characteristics and diabetes complications with type 1 diabetes (T1DM) or early onset type 2 diabetes (T2DM).

METHODS

The study covers 9 patients with MIDD, 33 patients with T1DM and 86 patients (age of onset ≤35years) with early onset T2DM, matched for sex, age at onset of diabetes, duration of diabetes. All patients with MIDD were confirmed as carrying the m.3243A>G mitochondrial DNA mutation. Serum HbA1c, beta-cell function, retinal and renal complications of diabetes, bone metabolic markers, lumbar spine and femoral neck BMD bone mineral density were compared to characterize the clinical features of all patients.

RESULTS

Nine patients were from five unrelated families, and the mean (SD) onset age of those patients was 31.2±7.2year. Two patients required insulin at presentation, and six patients progressed to insulin requirement after a mean of 7.2years. β-Cell function in the MIDD group was intermediate between T1DM and early-onset T2DM. In MIDD, four patients were diagnosed as diabetic retinopathy (4/9) and five patients (5/9) had macroalbuminuria. The number of patients with diabetic retinopathy and macroalbuminuria in the MIDD group was comparable to T1DM or early-onset T2DM. The rate of osteoporosis (BMD T-score<-2.5 SD) in the patient with MIDD was higher than the T1DM or early-onset T2DM group.

CONCLUSION

Our study indicates that of the nine subjects with MIDD, three patients (1-II-1, 1-II-3, 1-II-4) who came from the same family had a history of acute pancreatitis. Compared with T1DM or early-onset T2DM matched for sex, age, duration of diabetes, MIDD patients had the highest rate of osteoporosis.

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.