Does mitochondrial genome mutation in subjects with maternally inherited diabetes and deafness decrease severity of diabetic retinopathy?

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.

Cystoid macular changes on optical coherence tomography in a patient with maternally inherited diabetes and deafness (MIDD)-associated macular dystrophy

The clinical presentation and optical coherence tomography findings in a patient with maternally inherited diabetes and deafness (MIDD) are presented to highlight the presence of macular cystoid spaces in some patients with this disease. Typically, patients with MIDD demonstrate progression of a pigmentary maculopathy into areas of geographic macular atrophy. At the time of initial visit, the 30-year-old patient had large macular cystoid changes in addition to retinal pigmentary changes in both eyes. The cystoid changes responded to treatment with systemic immunosuppression and a topical carbonic anhydrase inhibitor (CAI), recurred when treated with topical CAI monotherapy, and finally resolved after an intravitreal triamcinolone acetonide injection. Over time, the retinal atrophy continued to progress, but the macular cysts did not recur. The patient received systemic immunosuppression for renal transplantation due to renal failure resulting from focal glomerulosclerosis. There was no evidence of diabetic retinopathy at any time during the five-and-a-half-year follow-up, and the patient retained good visual acuity in both eyes.

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.

Hypoxia and Dark Adaptation in Diabetic Retinopathy: Interactions, Consequences, and Therapy

In diabetes, retinal blood flow is compromised, and retinal hypoxia is likely to be further intensified during periods of darkness. During dark adaptation, rod photoreceptors in the outer retina are maximally depolarized and continuously release large amounts of the neurotransmitter glutamate-an energetically demanding process that requires the highest oxygen consumption per unit volume of any tissue of the body. In complete darkness, even more oxygen is consumed by the outer retina, producing a steep fall in the retinal oxygen tension curve which reaches a nadir at the depth of the mitochondrial-rich rod inner segments. In contrast to the normal retina, the diabetic retina cannot meet the added metabolic load imposed by the dark-adapted rod photoreceptors; this exacerbates retinal hypoxia and stimulates the overproduction of vascular endothelial growth factor (VEGF). The use of nocturnal illumination to prevent dark adaptation, specifically reducing the rod photoreceptor dark current, should ameliorate diabetic retinopathy.

Endocrine disorders in mitochondrial disease

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

The pathogenesis of early retinal changes of diabetic retinopathy

Recent successful trials of antibodies to vascular endothelial growth factor (VEGF) in diabetic retinopathy implicate this cytokine as a major cause of diabetic retinopathy (DR) and diabetic macular oedema (DME). The mechanisms which cause VEGF to be over-expressed to cause the vasculopathy are not entirely clear. This review explores the earliest changes to the retina in DR and the factors that predispose or prevent DR, including sleep apnoea, receptor degenerations laser treatment and VEGF polymorphism. The review also presents the evidence that retinal hypoxia, existing in the earliest stages, causes DR. This hypoxia is much increased by dark adaptation, indicating a new and possibly superior therapy.

Unusual occurrence of intestinal pseudo obstruction in a patient with maternally inherited diabetes and deafness (MIDD) and favorable outcome with coenzyme Q10

Maternally inherited diabetes and deafness (MIDD) has been related to an A to G transition in the mitochondrial tRNA Leu (UUR) gene at the base pair 3243. This subtype of diabetes is characterized by maternal transmission, young age at onset and bilateral hearing impairment. Besides diabetes and deafness, the main diagnostic features, a wide range of multisystemic symptoms may be associated with the A3243G mutation. Organs that are most metabolically active, such as muscles, myocardium, retina, cochlea, kidney and brain are frequently affected. Gastrointestinal tract symptoms are also common in patients with mitochondrial disease and constipation and diarrhea are the most frequent manifestations. However, there are few prior reports of intestinal pseudo obstruction in MIDD patients. Here we report the case of a patient with MIDD associated with the mtDNA A3243G mutation who developed chronic intestinal pseudo obstruction, and the introduction of Coenzyme Q10 as adjunctive therapy led to a solution of the pseudo obstruction.

Retinal and renal complications in patients with a mutation of mitochondrial DNA at position 3,243 (maternally inherited diabetes and deafness). A case-control study

AIMS/HYPOTHESIS

We assessed the prevalence and determinants of retinal and renal complications in patients with maternally inherited diabetes and deafness (MIDD).

METHODS

This was a multicentre prospective study comparing the prevalence of retinopathy and renal disease in 74 patients with MIDD and 134 control patients matched for sex, age and clinical presentation at onset of diabetes, duration of diabetes and current treatment. Comparisons were adjusted for HbA(1c) and hypertension.

RESULTS

In MIDD patients, HbA(1c) (7.6 +/- 1.6 vs 8.5 +/- 2.0%, p < 0.002), systolic blood pressure (126.6 +/- 16.2 vs 133.1 +/- 17.3 mmHg, p < 0.007) and prevalence of hypertension (33.8 vs 64.2%, p < 0.0001) were lower than in control patients. Prevalence of diabetic retinopathy was 3.7-fold lower in MIDD patients (6/74, 8 vs 40/134, 29.6%, p < 0.0001). Differences between groups remained significant after adjustment for hypertension, systolic blood pressure and HbA(1c). In MIDD, urinary albumin excretion (314.8 vs 80.1 mg/24 h, p = 0.035) and creatinine plasma levels (103.5 vs 82.2 micromol/l, p = 0.0178) were higher and GFR was lower. Impaired renal function (GFR <60 ml/min) was four- to sixfold more frequent in MIDD. Differences between MIDD and control diabetic patients further increased when adjusted for HbA(1c) and systolic blood pressure (p < 0.0001). Adjustment for treatment with an ACE inhibitor or angiotensin II receptor antagonist did not modify the results.

CONCLUSIONS/INTERPRETATION

This study indicates that diabetic retinopathy is less prevalent in MIDD than in control diabetes. This suggests that retinal alterations due to mitochondrial disease may have a protective role. By contrast, nephropathy is far more frequent in MIDD, suggesting the presence of a specific renal disease independent of diabetic nephropathy.

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.

Spare the rod and spoil the eye

This review presents a new unified view of the pathogenesis of three common causes of acquired retinal degenerative disease-diabetic retinopathy, age related macular degeneration, and retinopathy of prematurity. In these three conditions, angiogenesis has a predominant role in the development of sight threatening pathology. Angiogenesis is controlled by among other factors the expression of vascular endothelial growth factor (VEGF), which in turn is regulated by absolute and relative lack of oxygen. The severe pathological manifestations of these three conditions are not part of a general underlying disease process because they are peculiar to the eye, and the profound hypoxia that develops in normal retina during dark adaptation (rod driven hypoxia) is an adequate and elegant additional factor to explain their pathogenesis. A large number of experimental reports support this conclusion, although rod driven anoxia is not generally considered as a causal factor in ocular disease. However, the hypothesis can be critically tested, and also suggests novel methods of treatment and prevention of these conditions that may be simpler and more inexpensive than current therapies and that have a smaller potential for adverse effects.

Maternal transmission of diabetes

Type 2 diabetes mellitus represents a heterogeneous group of conditions characterized by impaired glucose homeostasis. The disorder runs in families but the mechanism underlying this is unknown. Many, but not all, studies have suggested that mothers are excessively implicated in the transmission of the disorder. A number of possible genetic phenomena could explain this observation, including the exclusively maternal transmission of mitochondrial DNA (mtDNA). It is now apparent that mutations in mtDNA can indeed result in maternally inherited diabetes. Although several mutations have been implicated, the strongest evidence relates to a point substitution at nucleotide position 3243 (A to G) in the mitochondrial tRNA(leu(UUR)) gene. Mitochondrial diabetes is commonly associated with nerve deafness and often presents with progressive non-autoimmune beta-cell failure. Specific treatment with Coenzyme Q10 or L-carnitine may be beneficial. Several rodent models of mitochondrial diabetes have been developed, including one in which mtDNA is specifically depleted in the pancreatic islets. Apart from severe, pathogenic mtDNA mutations, common polymorphisms in mtDNA may contribute to variations of insulin secretory capacity in normal individuals. Mitochondrial diabetes accounts for less than 1% of all diabetes and other mechanisms must underlie the maternal transmission of Type 2 diabetes. Possibilities include the role of maternally controlled environments, imprinted genes and epigenetic phenomena.

Insulin secretion and insulin sensitivity are normal in non-diabetic subjects from maternal inheritance diabetes and deafness families

BACKGROUND

The pathophysiological mechanism of diabetes mellitus in the presence of the 3243 A-G tRNALEU(UR) mitochondrial DNA mutation is thought to result from deficient insulin secretion. However, few subjects with normal glucose tolerance have been studied to determine the sequence of events resulting in the development of diabetes mellitus.

AIM

To determine whether abnormalities of insulin sensitivity, insulin secretion or glucose effectiveness are present in non-diabetic subjects with the 3243 A-G tRNALEU(UUR) mitochondrial DNA mutation.

METHODS

Twelve non-diabetic subjects with the mutation were compared with 12 controls, matched for age and anthropometric parameters, using both oral and intravenous glucose tolerance tests, the latter with Minimal Model analysis.

RESULTS

Following an oral glucose load we found significantly higher blood glucose levels at 90 min and 120 min and significantly higher insulin levels at 120 min and 180 min in non-diabetic subjects with the mutation but no difference in the insulinogenic indices at 30 min and 180 min. From the intravenous glucose tolerance test there was no difference in overall glucose tolerance, insulin sensitivity, first- or second-phase insulin secretion, proinsulin secretion or glucose effectiveness. Insulin-independent glucose disposal was increased in subjects with lower insulin sensitivity and declined with increasing age in subjects with the mutation but not in controls.

CONCLUSIONS

While there appear to be subtle defects of glucose handling in non-diabetic subjects with the 3243 mutation, these could not be explained by differences in insulin sensitivity or secretion.

Prevalence of macular pattern dystrophy in maternally inherited diabetes and deafness. GEDIAM Group

OBJECTIVE

To evaluate the prevalence of macular pattern dystrophy (MPD) in maternally inherited diabetes and deafness (MIDD), a new subtype of diabetes mellitus that cosegregates with a mutation of mitochondrial DNA (i.e., the substitution of guanine for adenine at position 3243 of leucine transfer RNA) and to report the clinical characteristics of MPD.

DESIGN

Prospective cohort study.

PARTICIPANTS

Forty-six patients from 29 families with an adenine-to-guanine mutation of mitochondrial DNA were recruited from a French collaborative multicenter study. Thirty-five patients had MIDD, 8 were asymptomatic children of MIDD patients, and 3 had MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes). The 33 MIDD patients with diabetes were matched for diabetes duration and gender with 33 patients with "common" type-2 diabetes to compare the prevalence of diabetic retinopathy (DR) in both series.

METHODS

All patients had a full ophthalmologic examination and fundus photographs.

MAIN OUTCOME MEASURES

The presence and severity of MPD and DR were assessed in each patient.

RESULTS

Thirty MIDD patients (85.7%) of 35 exhibited bilateral MPD characterized by linear pigmentation surrounding the macula and optic disc. In 24 of these 30 patients, visual acuity was 20/25 or more in both eyes. The prevalence of DR was 6% in MIDD patients with diabetes versus 15% for patients with common type-2 diabetes (a difference that was not significant, P = 0.23). The fundus of each of the eight asymptomatic children was normal. MPD was present in one of the three cases of MELAS.

CONCLUSION

The prevalence of MPD in MIDD is high. Its detection may be helpful for the diagnosis of this new subtype of diabetes, for which specific treatments may be proposed.

Mitochondrial DNA mutations are associated with both decreased insulin secretion and advanced microvascular complications in Japanese diabetic subjects

To assess the roles of various mitochondrial (Mt) DNA mutations in diabetic and nondiabetic subjects, we screened Mt DNAs at the 3243 base pair (bp) and its adjacent portion in unrelated Japanese diabetic and nondiabetic subjects. Furthermore, to clarify the clinical features of diabetic subjects harboring a Mt DNA mutation, we evaluated the ability of insulin secretion and microvascular complications in diabetic subjects. Five hundred thirty-seven diabetic patients and 612 unrelated nondiabetic subjects were recruited into this study. In Mt DNA analyses, Mt DNA was isolated from peripheral leukocytes of the subjects, and then an Mt DNA fragment surrounding the tRNA(Leu(UUR)) site was amplified by the polymerase chain reaction (PCR) using two sets of primers. These fragments were further digested with three kinds of restriction endonucleases and were subjected to agarose gel electrophoresis. When a mutation was present, Mt DNA fragments were directly sequenced with an autosequencer. Baseline characteristics in all subjects were examined, and microvascular complications and insulin secretory capacity in diabetic subjects were newly evaluated. Eight kinds of Mt DNA mutations, which were point mutations, were found in 74 subjects. Each affected subject had only one mutation in the Mt DNA examined. Among them, the mutations at np 3316, 3394, 3593, and 3391 were accompanied by amino acid replacement. Thirty-eight diabetic patients were affected (7.1%), including two subjects with a point mutation at np 3243, and 26 nondiabetic subjects were affected (4.2%). Thus, there was a higher prevalence in diabetic subjects than in nondiabetic subjects. There was no significant difference in the prevalence of maternally inherited diabetes between these two groups. The mean level of urinary C-peptide excretion was lower in diabetic subjects with an Mt DNA mutation (DM+) than in those without it (DM-). Although the prevalence of hypertension in DM+ was higher than that in DM-, diabetic retinopathy and nephropathy in DM+ were problematic, in comparison with those in DM-, when statistical corrections were performed for the effect of hypertension. Furthermore, a strategy based on logistic regression analysis revealed that advanced retinopathy and decreased urinary C-peptide excretion in all diabetic subjects studied were strongly related to the presence of Mt DNA mutation. Our results suggest that Mt DNA mutations in Japanese diabetic subjects are related to the development of diabetes, and also that these mutations are associated with not only a decrease in insulin secretion but also advanced diabetic microvascular complications.