Adult-onset diabetes mellitus and neurosensory hearing loss in maternal relatives of MELAS patients in a family with the tRNA(Leu(UUR)) mutation

Negative correlation between organ heteroplasmy, particularly hepatic heteroplasmy, and age at death revealed by post-mortem studies of m.3243A > G cases

Mitochondrial DNA m.3243A > G mutation causes mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) and its associated multi-organ disorders, including diabetes. To clarify associations between m.3243A > G organ heteroplasmy and clinical phenotypes, including the age at death, we combined genetic and pathological examinations from seven unreported and 36 literature cases of autopsied subjects. Clinical characteristics of subjects were as follows: male, 13; female, 28; unknown, 2; the age at death, 36.9 ± 20.2 [4-82] years; BMI, 16.0 ± 2.9 [13.0-22.3]; diabetes, N = 21 (49%), diabetes onset age 38.6 ± 14.2 years; deafness, N = 27 (63%); stroke-like episodes (StLEp), N = 25 (58%); congestive heart failure (CHF), N = 15 (35%); CHF onset age, 51.3 ± 14.5 years. Causes of death (N = 32) were as follows: cardiac, N = 13 (41%); infection, N = 8 (25%); StLEp, N = 4 (13%); gastrointestinal, N = 4 (13%); renal, N = 2 (6%); hepatic, N = 1 (2%). High and low heteroplasmies were confirmed in non-regenerative and regenerative organs, respectively. Heteroplasmy of the liver, spleen, leukocytes, and kidney for all subjects was significantly associated with the age at death. Furthermore, the age at death was related to juvenile-onset (any m.3243A > G-related symptoms appeared before 20) and stroke-like episodes. Multiple linear regression analysis with the age at death as an objective variable showed the significant contribution of liver heteroplasty and juvenile-onset to the age at death. m.3243A > G organ heteroplasmy levels, particularly hepatic heteroplasmy, are significantly associated with the age at death in deceased cases.

Macular findings expedite accurate diagnosis of MIDD in a young female patient with newly diagnosed diabetes

Purpose

To report a case of a 34-year-old female patient with newly diagnosed Maternally Inherited Diabetes and Deafness (MIDD) in the setting of undifferentiated macular dystrophy and newly discovered diabetes.

Observations

A 34-year-old woman presented to the retina service with new-onset diabetes and a history of hydroxychloroquine use. Ophthalmologic examination showed findings early in the patient's presentation that within the context of her recent diabetes diagnosis and family history pointed to MIDD as the specific cause of the patient's many different symptoms. This diagnosis was further supported through obtaining previous ophthalmic images of the patient's mother demonstrating circular areas of geographic atrophy seen in advanced MIDD, and the diagnosis was confirmed through genetic testing.

Conclusions and importance

As was observed in the patient discussed in this manuscript, recognition of macular dystrophy findings suggestive of MIDD can hasten a timely diagnosis for a patient with diabetes of unspecified etiology. Additionally, knowledge of the underlying cause being MIDD can optimize care for patients in terms of treatment, understanding their risk for various diabetes complications, screening for additional systemic manifestations, and initiating valuable genetic counseling for patients and their families. Given these factors and the surprisingly high prevalence of MIDD among diabetes patients, increased awareness of MIDD and its manifestations can help to optimize diagnosis and management for these patients.

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.

Comprehensive review on lactate metabolism in human health

Metabolic pathways involved in lactate metabolism are important to understand the physiological response to exercise and the pathogenesis of prevalent diseases such as diabetes and cancer. Monocarboxylate transporters are being investigated as potential targets for diagnosis and therapy of these and other disorders. Glucose and alanine produce pyruvate which is reduced to lactate by lactate dehydrogenase in the cytoplasm without oxygen consumption. Lactate removal takes place via its oxidation to pyruvate by lactate dehydrogenase. Pyruvate may be either oxidized to carbon dioxide producing energy or transformed into glucose. Pyruvate oxidation requires oxygen supply and the cooperation of pyruvate dehydrogenase, the tricarboxylic acid cycle, and the mitochondrial respiratory chain. Enzymes of the gluconeogenesis pathway sequentially convert pyruvate into glucose. Congenital or acquired deficiency on gluconeogenesis or pyruvate oxidation, including tissue hypoxia, may induce lactate accumulation. Both obese individuals and patients with diabetes show elevated plasma lactate concentration compared to healthy subjects, but there is no conclusive evidence of hyperlactatemia causing insulin resistance. Available evidence suggests an association between defective mitochondrial oxidative capacity in the pancreatic β-cells and diminished insulin secretion that may trigger the development of diabetes in patients already affected with insulin resistance. Several mutations in the mitochondrial DNA are associated with diabetes mellitus, although the pathogenesis remains unsettled. Mitochondrial DNA mutations have been detected in a number of human cancers. d-lactate is a lactate enantiomer normally formed during glycolysis. Excess d-lactate is generated in diabetes, particularly during diabetic ketoacidosis. d-lactic acidosis is typically associated with small bowel resection.

Prevalence of mitochondrial diabetes in southwestern Finland: a molecular epidemiological study

Mitochondrial diabetes and deafness (MIDD) is a subtype of diabetes mellitus (DM) that most commonly results from the m.3243A > G mutation in mitochondrial DNA (mtDNA). Sensorineural hearing loss is a typical accompanying feature. Previous studies have suggested a prevalence of ~1-1.5 % for MIDD. We studied the molecular epidemiology of MIDD among young (aged 18-45 years) adults in a defined population in southwestern Finland. Of the identified cohort of 1,532 patients with DM, we received blood samples of 299 patients and analyzed them for the m.3243A > G mutation and for mtDNA haplogroups. We found three DM patients (1.0 %) with the m.3243A > G mutation. All the three patients with DM and m.3243A > G also had severe hearing impairment that required use of hearing aid. MtDNA haplogroup U was more prevalent among patients with maternal family history of DM. We conclude that among young adults, ~1 % of all DM is associated with the m.3243A > G mutation. We suggest that all patients with both DM and hearing impairment, at least in this age group, should undergo investigation for this mutation. Furthermore, our results suggest that mtDNA haplogroup U is associated with maternal family history of DM.

Role of mitochondrial variation in maternally inherited diabetes and deafness syndrome

Maternally inherited diabetes and deafness syndrome is caused by the mitochondrial deoxyribonucleic acid mutation 3243 A>G (where A = adenine and G = guanine). The degree of heteroplasmy of the mitochondrial deoxyribonucleic acid may correlate with the rate of progression of the hearing loss. This has important implications for counselling patients with this pathology. Cochlear implantation is a successful method of rehabilitation for patients with hearing loss as part of this syndrome.

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.

Accurate consent for insertion and later removal of grommets

Each year in the UK over 30 000 patients undergo insertion of grommets. The grommet insertion may cause many problems like persistent otorrhoea, scarred drum, retraction pockets and retention. The grommets may be extruded from the middle ears by the normal epithelial migration mechanism once they have served their purpose. These may become infected and require removal. We have analysed the Department of Health Hospital Episode Statistics relating to the insertion and removal of grommets (ventilation tubes). We have shown that 7.6 per cent of patients who have grommets inserted will have grommets removed.

Diabète et cytopathies mitochondriales : données anatomo-pathologiques

Maternal diabetes associated with neural deafness is designated as MIDD (maternal inherited diabetes and deafness); it is linked to a A3243G tRNA leucine gene mutation. The disease course is progressive and involvement of other systems is frequent. In most cases, macular pattern dystrophy is present. Muscular lesions are characteristic of mitochondrial myopathies. Mitochondrial abnormalities have also been observed in pancreas, heart, kidney, smooth muscle of the digestive tract with variable heteroplasmy levels. MIDD may present as a single syndrome or is part of MELAS or Kearns-Sayre syndrome.

A review of cochlear implantation in mitochondrial sensorineural hearing loss

OBJECTIVE

Mitochondrial sensorineural hearing loss (SNHL) may be nonsyndromic (occurring in isolation), associated with the A1555G mutation in the MTRNR1 gene. Mitochondrial SNHL may also be syndromic, associated with the A3243G point mutation in the MTTL1 gene. In syndromic cases-mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS), maternally inherited diabetes and deafness, Kearns-Sayre syndrome, and chronic progressive external ophthalmoplegia-the SNHL compounds already existing disabilities. The genetic basis for mitochondrial SNHL and postulated sites of pathologic changes are discussed.

DATA SOURCES

Sources used were relevant clinical and basic science publications.

STUDY SELECTION

A search of the entire databases of Medline and Web of Science, using various subject headings and free-text terms, was used to identify patients with mitochondrial disease having cochlear implants.

DATA EXTRACTION

The data from publications were critically reviewed and tabulated to assess implantation outcomes.

DATA SYNTHESIS

The data were not amenable to formal meta-analysis or valid data summarization, other than descriptive statistics.

CONCLUSIONS

There is an increasing awareness of the prevalence of mitochondrial SNHL and its progressive nature. High-risk candidates warrant genetic testing and family screening. Correlating the data for mitochondrial SNHL as a treatable entity is important, and the authors present an overview of these patients successfully rehabilitated by cochlear implantation.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Endocrine disorders in two sisters affected by MELAS syndrome

A variety of endocrine and metabolic defects, including hypothalamopituitary hypofunction and diabetes mellitus, has been reported in association with mitochondrial disorders. We describe two sisters affected by mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome in whom DNA analysis showed an A-->G transition at the 3243rd nucleotide position on the transfer RNALeu(UUR) gene with 65% and 45% of mutant-type mitochondrial DNA present in the blood cells of the younger and the older sister, respectively. The younger sister had severe involvement of the central nervous system with mental retardation, epilepsia partialis continua, and strokelike episodes. Endocrine investigations showed an extensive neuroendocrine dysfunction with growth hormone deficiency, hypothalamopituitary hypothyroidism, prepubertal gonadotropin levels, and absence of any secondary sexual characteristics at the age of 12 6/12 years. The neurologically normal older sister was affected by diabetes mellitus and had normal hypothalamopituitary function. Our report confirms that the endocrine system can be affected differently by the same mitochondrial DNA mutation, depending on the heteroplasmia phenomenon. A complete endocrine evaluation must be performed in patients affected by mitochondrial disease and the existence of a mitochondrial disorder should be taken into account in patients with endocrine abnormalities, even if neuromuscular signs are lacking.

Threshold effect and tissue specificity. Implication for mitochondrial cytopathies

Mitochondrial cytopathies present a tissue specificity characterized by the fact that even if a mitochondrial DNA mutation is present in all tissues, only some will be affected and induce a pathology. Several mechanisms have been proposed to explain this phenomenon such as the appearance of a sporadic mutation in a given stem cell during embryogenesis or mitotic segregation, giving different degrees of heteroplasmy in tissues. However, these mechanisms cannot be the only ones involved in tissue specificity. In this paper, we propose an additional mechanism contributing to tissue specificity. It is based on the metabolic expression of the defect in oxidative phosphorylation (OXPHOS) complexes that can present a biochemical threshold. The value of this threshold for a given OXPHOS complex can vary according to the tissue; thus different tissues will display different sensitivities to a defect in an OXPHOS complex. To verify this hypothesis and to illustrate the pathological consequences of the variation in biochemical thresholds, we studied their values for seven OXPHOS complexes in mitochondria isolated from five different rat tissues. Two types of behavior in the threshold curves can be distinguished corresponding to two modes of OXPHOS response to a deficiency. We propose a classification of tissues according to their type of OXPHOS response to a complex deficiency and therefore to their threshold values.

Infantile encephalopathy associated with the MELAS A3243G mutation

MELAS syndrome is typically characterized by normal early development and childhood-onset recurrent neurologic deficits (stroke-like episodes), seizures, short stature, lactic acidosis, and ragged red fibers on muscle biopsy specimens. It is usually, but not invariably, associated with the A3243G point mutation in the mitochondrial DNA tRNALeu(UUR) gene. We report 3 unrelated children with the A3243G mutation who presented with severe psychomotor delay in early infancy. One patient's clinical picture was more consistent with Leigh syndrome, with apneic episodes, ataxia, and bilateral striatal lesions on brain magnetic resonance imaging (MRI). The second patient had generalized seizures refractory to treatment and bilateral occipital lesions on brain MRI. The third child had atypical retinal pigmentary changes, seizures, areflexia, and cerebral atrophy on brain MRI. All patients had several atypical features in addition to early onset: absence of an acute or focal neurologic deficit, variable serum and cerebrospinal fluid lactate levels, lack of ragged red fibers in muscle biopsy specimens. The proportion of mutant mtDNA in available tissues was relatively low (range, 5% to 51% in muscle; 4% to 39% in blood). These observations further extend the phenotypic expression of the A3243G "MELAS" mutation. Our findings confirm previous observations that there is poor correlation between abundance of mutant mtDNA in peripheral tissues and neurologic phenotype. This suggests that other factors contribute to the phenotypic expression of this mutation.

Cell cycle of myocytes of cardiac and skeletal muscle in mitochondrial myopathy

Patients who have mitochondrial myopathy can present with specific pathological conditions (eg, diabetes mellitus and deafness). A 36-year-old woman presented with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). An investigation was conducted into whether the abnormalitiy of mitochondrial DNA (a T to C transition at position 3271 in the mitochondrial tRNA [Leu(UUR)] gene) influences nuclear DNA synthesis by cells in the heart, skeletal muscles, and brain. Myocardium, skeletal muscle, and brain tissues were stained with hematoxylin-eosin, and Masson trichrome for histopathology. Target nuclei taken from the myocardial and skeletal muscles and brain tissue were purified after removing debris by the modified Hedley method. These nuclei were stained with propidium iodide (PI) for analysis by flow cytometry. The number of nuclei in the G2M phase was bigger in myocytes of MELAS than in normal myocytes (Control) (MELAS myocyte: Control myocyte=24.9+/-7.3: 6.1+/-1.6%, p<0.005), but there was no significant increase in the G2M phase in brain tissue. The G1 phase was far more reduced in MELAS myocytes and skeletal muscle than in Controls (MELAS myocyte: Control myocyte=65.8+/-9.1: 88.0+/-3.2%, p<0.005; MELAS skeletal muscle: Control skeletal muscle=85.1+/-2.2: 90.1+/-3.2%, p<0.05), while there was no significant decrease of nuclei in the G1 phase in brain tissue. Increased amount of nuclei in the G2M phase in cardiac myocytes and skeletal muscle cells compared with that in neurons might depend on the capacity for proliferation and differentiation of these cells as compared with brain tissue. It was concluded that the mitochondrial DNA mutation (3271T-to-C) of MELAS may influence the nuclear DNA synthesis of cells in various tissues depending on their level of mitotic activity.

Autoimmune IDDM in a sporadic MELAS patient with mitochondrial tRNA(Leu(UUR)) mutation

We report a 28-year-old young male with MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) presenting with two previous episodes of stroke-like manifestation, lactic acidosis and mitochondrial cardiomyopathy. He was also affected with insulin-dependent diabetes mellitus (IDDM), as diagnosed by the experience of diabetic ketoacidosis (DKA), and dependence on insulin therapy. On admission, the serum lactate level was found to be increased to 5.4 mmol/l, and plasma glucose level to 7.9 mmol/l with haemoglobin A1c 8.4%, while he was using insulin 26-30 units per day. Physical examination revealed a short stature male of height of 150 cm and weight of 49 kg. Mild mental retardation with bilateral sensorineural hearing impairment was observed. After glucagon stimulation, C-peptide levels rose from 0.46 nmol/l to 0.53 nmol/l, indicative of impaired insulin secretion. Anti-glutamate decarboxylase (anti-GAD) antibody was positive. In addition, human leucocyte associated antigen (HLA) typing showed DR3 and DR4, suggesting the strong contribution of autoimmunity to the pathogenesis of IDDM in this patient. Moreover, the result of a treadmill exercise test was positive due to inferior wall myocardial ischaemia. Cardiac catheterization and endomyocardial biopsy disclosed a normal coronary angiogram and confirmed the diagnosis of mitochondrial cardiomyopathy. Molecular genetic analysis of his family revealed a sporadic occurrence of mitochondrial DNA (mtDNA) mutation at base pair (bp) 3243. The degree of heteroplasmy of mtDNA mutation from a total of 19 passages of skin-derived fibroblasts from this patient showed a slightly downward trend. This extremely rare case of sporadic MELAS syndrome with autoimmune IDDM harbouring mtDNA mutation highlights the possible pathogenetic role of mtDNA mutations in autoimmune disease.

Cochlear origin of hearing loss in MELAS syndrome

There have been few studies investigating the mechanism and nature of the hearing loss that occurs in the mitochondrial disorders. We studied 18 patients with the MELAS A3243G point mutation from four different kindreds. Pure tone audiometry, speech discrimination testing, acoustic reflexes, tympanometry, and brain stem auditory evoked responses were performed to localize the site of pathology in the auditory pathways. In 12 patients, we performed electrocochleography and otoacoustic emissions to assess cochlear involvement. Neuroimaging and promontory nerve stimulation were performed to exclude retrocochlear pathology. Audiological testing confirmed sensorineural hearing loss in 14 of the 18 patients studied; hearing loss was usually gradual in onset, was symmetrical, and initially affected the higher frequencies. In some patients, there were features that distinguished the hearing loss from presbyacusis, including a young age at onset, asymmetrical involvement, stepwise progression, and partial recovery. We treated one patient who had profound bilateral hearing loss with cochlear implantation; this restored good functional hearing. Hearing loss in MELAS syndrome appears to be due to dysfunction of the cochlea, probably resulting from metabolic failure of the stria vascularis and outer hair cells. Cochlear implantation is a therapeutic option worth considering in those patients who become deaf.

Macular pattern retinal dystrophy, adult-onset diabetes, and deafness: a family study of A3243G mitochondrial heteroplasmy

PURPOSE

To correlate mitochondrial DNA (mtDNA) mutation with phenotypic expression in three members of a Finnish family with macroreticular pattern dystrophy, non-insulin-dependent diabetes mellitus, and deafness.

METHODS

A multiplex polymerase chain reaction/allele-specific oligonucleotide method was used to screen 10 mtDNA point mutations known to cause mitochondrial DNA disorders, often characterized by myopathy, retinopathy, or both. Quantitative analysis of mutant mitochondrial DNA was performed in three tissue types in each of three family members by determining the percentage of mutant mtDNA in blood, buccal cells, and hair follicles.

RESULTS

A heteroplasmic A3243G mtDNA point mutation was found in each of the three family members studied. Heteroplasmy refers to the coexistence of normal and mutant mitochondria in the same cell. The average percentage of mutant heteroplasmy ranged from 11% to 25%. The severity of disease symptoms did not appear to correlate with the average degree of mutant heteroplasmy in the three tissues analyzed.

CONCLUSIONS

Molecular confirmation in this family emphasizes the importance of mitochondrial DNA mutation analysis in patients with macular pattern retinal dystrophy and other mitochondrial associated nonocular disease, such as non-insulin-dependent diabetes mellitus and deafness. The detection of a disease-associated mitochondrial DNA mutation warrants genetic counseling, appropriate patient follow-up, and possibly the molecular testing of other at-risk family members.

Mitochondrial DNA mutations and pathogenesis

Approximately there years ago, this journal published a review on the clinical and molecular analysis of mitochondrial encephalomyopathies, with emphasis on defects in mitochondrial DNA (mtDNA). At the time, approximately 30 point mutations associated with a variety of maternally-inherited (or rarely, sporadic) disorders had been described. Since that time, almost twenty new pathogenic mtDNA point mutations have been described, and the pace of discovery of such mutations shows no signs of abating. This accumulating body of data has begun to reveal some patterns that may be relevant to pathogenesis.

Audiologic findings in patients with a point mutation at nucleotide 3,243 of mitochondrial DNA

A mitochondrial tRNALeu(UUR) mutation at nucleotide 3,243 is known to be found in most patients with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) and has also been identified in several families with maternally inherited diabetes mellitus and hearing loss. We report here audiologic features in patients with hearing loss associated with the mutation. Four patients without and five with MELAS were studied. Most of the patients had bilateral progressive sensorineural hearing loss. The most common shape of the audiogram was sloping, while cases in the advanced stages had flat audiograms. Speech discrimination scores were generally poor and did not parallel the degree of hearing loss. The present study suggests that the lesion for hearing loss could include both cochlear and retrocochlear involvement, but does not demonstrate a significant difference in the audiologic findings between patients with and without MELAS.

Screening for the mitochondrial DNA A3243G mutation in children with insulin-dependent diabetes mellitus

Since recent studies demonstrated the occurrence of the mitochondrial DNA (mtDNA) mutation A3243G in patients with adult-onset diabetes, an investigation was undertaken to determine the frequency of this mutation in a pediatric population with insulin-dependent diabetes mellitus (IDDM). DNA was extracted from peripheral blood of 270 pediatric patients with IDDM. The presence of the mtDNA A3243G mutation was screened for by minisequencing and mutation-specific ApaI endonuclease restriction after polymerase chain reaction (PCR) amplification of mtDNA. The A3243G mtDNA mutation was not found in any IDDM patients examined. This mutation is uncommon in children with IDDM from various ethnic and racial groups. Therefore, the contribution of the mutation to the pathogenesis of IDDM, if any, is minimal.

Non-insulin-dependent diabetes mellitus in childhood and adolescence

NIDDM in children and adolescents represents a heterogeneous group of disorders with different underlying pathophysiologic mechanisms. Most subtypes of NIDDM that occur in childhood are uncommon, but some, such as early onset of "classic" NIDDM, seem to be increasing in prevalence. This observed increase is thought to be caused by societal factors that lead to sedentary lifestyles and an increased prevalence of obesity. In adults, hyperglycemia frequently exists for years before a diagnosis of NIDDM is made and treatment is begun. Microvascular complications, such as retinopathy, are often already present at the time of diagnosis. Children are frequently asymptomatic at the time of diagnosis, so screening for this disorder in high-risk populations is important. Screening should be considered for children of high-risk ethnic populations with a strong family history of NIDDM with obesity or signs of hyperinsulinism, such as acanthosis nigricans. Even for children in these high-risk groups who do not yet manifest hyperglycemia, primary care providers can have an important role in encouraging lifestyle modifications that might delay or prevent onset of NIDDM.

Lactic acidosis and other mitochondrial disorders

The ability of mitochondria to oxidize substrates and generate energy is integral to normal homeostasis and to the ability of cells to survive in the face of impending energy failure. Lactic acidosis is a common and readily apparent biochemical marker for mitochondrial dysfunction. However, lactic acidosis represents only the most obvious example in which acquired or congenital abnormalities of mitochondrial oxidative phosphorylating capacity contribute to the pathobiology and phenotypic expression of a broad spectrum of clinical disorders. Consequently, interventions that improve mitochondrial function or prevent mitochondrial energy failure may have widespread therapeutic implications.

Monozygotic twins with MELAS-like syndrome lacking ragged red fibers and lactacidaemia

Typical cases of MELAS present a combination of clinical and neuroradiological features, lactacidaemia, and ragged red fibers (RRFs) in striated muscle. We have observed a MELAS-like syndrome in monozygotic twins. They developed seizures typically in conjunction with physical exertion, sleep deprivation or febrile episodes. Stroke-like episodes occurred usually during seizures. In twin 2 the course was fatal at age 20 years. Neuroradiological findings were typical of MELAS. Plasma lactate was normal in both. CSF lactate was normal in twin 1 and normal/elevated in twin 2. RRFs were not seen in muscle biopsies of the twins. Complex I activity was reduced in muscle in twin 1. Brain tissue removed at epilepsy surgery in twin 2 showed the presence of mitochondrial angiopathy. The commonest mitochondrial DNA mutation in MELAS, at base pair 3243, was absent. Lactacidaemia and mitochondrial myopathy with RRFs constitute part of the diagnostic criteria of MELAS. However, the absence of these features does not exclude mitochondrial disorder with the serious manifestations of MELAS (seizures and stroke-like episodes) as seen in these twins.

The expanding clinical phenotype of the tRNA(Leu(UUR)) A-->G mutation at np 3243 of mitochondrial DNA: diabetic embryopathy associated with mitochondrial cytopathy

We describe a family which demonstrates and expands the extreme clinical variability now known to be associated with the A-->G transition at nucleotide position 3243 of the mitochondrial DNA. The propositus presented at birth with clinical manifestations consistent with diabetic embryopathy including anal atresia, caudal dysgenesis, and multicystic dysplastic kidneys. His co-twin was normal at birth, but at 3 months of life, presented with intractable seizures later associated with developmental delay. The twins' mother developed diabetes mellitus type I at the age of 20 years and gastrointestinal problems at 22 years. Since age 19 years, the maternal aunt has had recurrent strokes, seizures, mental deterioration and deafness, later diagnosed as MELAS syndrome due to the tRNA(Leu(UUR)) A-->G mutation. A maternal uncle had diabetes mellitus type I, deafness, and normal intellect, and died at 35 years after recurrent strokes. This pedigree expands the known clinical phenotype associated with tRNA(Leu(UUR)) A-->G mutation and raises the possibility that, in some cases, diabetic embryopathy may be due to a mitochondrial cytopathy that affects both the mother's pancreas (and results in diabetes mellitus and the metabolic dysfunction associated with it) and the embryonic/fetal and placental tissues which make the embryo more vulnerable to this insult.

Insulin resistance associated with maternally inherited diabetes and deafness

Maternally inherited diabetes and deafness (MIDD) is a form of diabetes associated with mutation of mitochondrial DNA (mtDNA) that occurs in 1% to 2% of individuals with diabetes. Understanding the clinical course and abnormalities in insulin secretion and action in affected individuals should allow better understanding of how this genetic defect alter glucose metabolism. We report the clinical course of three individuals with mtDNA mutations and deafness. Subjects no. 1 and 2 had diabetes not yet requiring insulin therapy, and subject no. 3, the son of subject no. 2, had normal glucose tolerance. Defective oxidative phosphorylation (OXPHOS) based on OXPHOS enzymology of skeletal muscle biopsy of subjects no. 1 and 2 showed activity of less than 5% of the tolerance level in complex III for subject no. 1 and in complexes I, I + III, and IV for subject no. 2. Assessing insulin secretion using insulin response to intravenous glucose and insulin sensitivity based on minimal model analysis of an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT), first-phase insulin secretion was abnormal in subjects no. 1 and 2 and normal in subject no. 3 (AUC, 57, 93, and 1,235 pmol/L, respectively). In contrast, all three subjects had low insulin sensitivity indices (0.04, 0.14, and 0.27 x 10-4 x min/pmol/L, respectively). Subject no. 2, who underwent three FSIGT studies over a 16-month interval, showed transient improvement in insulin release in response to modification of diet and exercise (first-phase insulin AUC, 57 pmol/min v 287 pmol/min 10 months later; fasting insulin, 97 pmol/L v 237 pmol/L 10 months later), but by 16 months, first-phase insulin release and fasting insulin had decreased (AUC, 64 and 136 pmol/L, respectively) despite higher fasting glucose. We conclude that in our subjects with MIDD, insulin resistance is present and appears to precede defects in insulin release.

Bilateral sensorineural hearing loss associated with the point mutation in mitochondrial genome

Mitochondrial DNA (mtDNA) mutation associated with sensorineural hearing loss (SNHL) has previously been described in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) and in aminoglycoside-induced deafness. The authors of this study report three cases of SNHL associated with mtDNA mutation (3243A-->G). They examined the clinical features of this type of SNHL by audiologic studies and examined the mtDNA mutation by the polymerase chain reaction technique. In the three cases described, the SNHL had an adult onset and was bilateral and symmetrical. All patients had adult-onset diabetes mellitus. Audiologic studies revealed that the SNHL in all patients derived from the cochlea rather than from retrocochlear sites. It is presumed that mtDNA mutation results in mitochondrial dysfunction in cochlear tissues (i.e., hair cells and stria vascularis) and in neurons of the auditory pathway. Genetic analysis of mtDNA offers new insight into the diagnosis and treatment of SNHL.

Heteroplasmy levels of a mitochondrial gene mutation associated with diabetes mellitus decrease in leucocyte DNA upon aging

We showed previously that a mutation in the mitochondrial tRNALeu(UUR) gene at position 3243 associates with maternally inherited diabetes and deafness (MIDD). This mutation shows heteroplasmy in DNA from peripheral blood and other tissues. To examine whether heteroplasmy levels in peripheral blood DNA change upon aging, heteroplasmy levels were determined in DNA samples from peripheral blood, collected recently and 1.5-6 years ago, from 18 individuals carrying the 3243 mutation. It was found that 17 out of 18 carriers showed a decrease upon aging (P = 0.001), the average change being -0.69 +/- 0.61% per year. These data indicate a continuous selection against haematopoietic (precursor) cells carrying high levels of the 3243 mutation. Moreover, they imply that heteroplasmy levels may decrease below the detection limit if DNA from peripheral blood is analyzed from elderly individuals. DNA from oral mucosa cells was found to be a good alternative as heteroplasmy levels for the 3243 mutation are on the average 1.7 fold higher than in DNA from peripheral blood.

Auditory findings in patients with maternally inherited diabetes and deafness harboring a point mutation in the mitochondrial transfer RNA(Leu) (UUR) gene

Five patients with sensorineural hearing loss, who harbored a point mutation in the mitochondrial transfer RNA (tRNA) gene tRNA(Leu) (UUR), from five unrelated family pedigrees were examined. In these families diabetes and deafness were maternally inherited. Bilateral hearing was more severely impaired at higher frequencies. Audiometric test results revealed that hearing loss involved the cochlea. Hearing gradually deteriorated; the progression rate ranged from 1.5 to 7.9 dB per year. Proportion of mutant mitochondrial DNAs (mtDNAs) in the leukocytes was not related to the rate or degree of hearing loss, although hearing loss appeared at a younger age in patients with higher heteroplasmy. We speculate that after the proportion of damaged mtDNAs, mostly as a result of mutation, exceeds the expression threshold for deficiencies in mitochondrial protein synthesis and oxygen consumption, a drop in adenosine triphosphate level could lead to an imbalance of ion concentration, resulting in cell death in the cochlea.

Screening for mtDNA diabetes mutations in Pima Indians with NIDDM

More than half of the Pima Indians over age 35 years have non-insulin-dependent (type II) diabetes mellitus (NIDDM). Extensive data indicate the importance of maternal diabetes in determining their risk for diabetes. Generally, the risk of having NIDDM is higher in patients with affected mothers than affected fathers. This has been attributed to intrauterine factors, but recently mitochondrial inheritance has been raised as an alternative hypothesis. In other populations, several families and individuals with diabetes due to a mitochondrial DNA point mutation at nucleotide 3243 in the tRNA(leu(UUR)) gene have been described, as has one family with a 10.4 kb mitochondrial DNA duplication/deletion. We tested whether these specific mitochondrial gene mutations could explain a portion of the excess maternal transmission seen in the Pima Indians. Mitochondrial DNA obtained from blood lymphocytes of 148 Pima Indians with NIDDM was screened both for the point mutation at nt 3243, and the 10.4 kb duplication/deletion. Neither of these mutations was detected, and although a small proportion of the excess maternal transmission in Pima Indians could still be due to yet undescribed mitochondrial mutations or imprinted nuclear genes, our data support the role of the intrauterine environment in this population.

Is there an excess in maternal transmission of NIDDM?

Family studies have demonstrated that there is a strong genetic component to the aetiology of non-insulin-dependent diabetes mellitus (NIDDM), although the mode of inheritance is unknown. A number of recent family history studies, including one in Mexican Americans, have suggested that there is an excess of maternal transmission of NIDDM. Family history studies are subject to various types of bias, however, and the potential for bias in many of these studies has not been thoroughly evaluated. We therefore tested the hypothesis that diabetes is more likely to be transmitted from mothers than from fathers using data collected from a large family study of low-income Mexican Americans in San Antonio, Texas. The parents and offspring from 318 different nuclear families attended our medical clinic, where they received a 2-h oral glucose test. Diabetes was diagnosed on the basis of World Health Organization criteria. The sibships were classified into diabetic sibships (at least one sibling in the sibship was diabetic; n = 54) and non-diabetic siblings (no diabetic siblings; n = 264). The prevalence of diabetes among mothers of diabetic siblings was 61.4% (27 of 44) compared to 64.3% (18 of 28) among fathers of diabetic siblings (rate ratio = 0.95; 95% confidence interval; 0.51-1.84). For the non-diabetic sibships, the prevalence of diabetes was 31.7% (78 of 246) and 28.9% (37 of 128) among mothers and fathers, respectively (rate ratio = 1.09; 95% confidence interval: 0.73-1.67). These data provide no evidence for an excess maternal transmission of diabetes in Mexican Americans.

Diabetes mellitus carrying a mutation in the mitochondrial tRNA(Leu(UUR)) gene

We screened 214 Japanese NIDDM (non-insulin-dependent) diabetic patients with a family history of diabetes for mutations in the mitochondrial tRNA(Leu(UUR)) gene using polymerase chain reaction-restriction fragment length polymorphism and direct sequencing. Six patients were identified as having an A to G transition at position 3243 (3243 mutation), but no patients were detected with a T to C transition at position 3271, in the mitochondrial tRNA(Leu(UUR)) gene. These two mutations were not present in 85 healthy control subjects. It was disclosed that the patients' mothers were also affected by diabetes mellitus in five of the six cases. In these six affected patients, the 3243 mutation shows variable phenotypes, such as the degree of multiple organ involvement, intrafamilial and interfamilial differences in disease characteristics, and the degree of the involvement of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) phenotype. Endocrinological examinations revealed that those diabetic patients with the 3243 mutation show not only beta-cell dysfunction, but also a defect in alpha-cell function, which is considered characteristic of diabetes with the 3243 mutation. When compared with 50 selected diabetic control subjects without the 3243 mutation, whose mothers, but not fathers, were found to have diabetes, it was established statistically that those with the 3243 mutation possess the following clinical characteristics; 1) the age of diabetes onset is lower, 2) they have lean body constitutions, and 3) they are more likely to be treated with insulin than control subjects. We suggest that diabetes with the 3243 mutation possesses phenotypes distinct from those in common forms of diabetes.

Non-Mendelian mitochondrial inheritance as a cause of progressive genetic sensorineural hearing loss

Awareness of non-Mendelian mitochondrial inheritance and of its role as an agent of genetic sensorineural hearing loss (SNHL) is recent. Mitochondria are passed on exclusively from the ovum to all the offspring of both sexes, a novel pattern of inheritance. Owing to the critical role of mitochondria in cellular energy metabolism, deletions or point mutations of the mitochondrial DNA often cause progressive SNHL and a variety of disorders in other organ systems (mitochondrial cytopathies). The clinical expression of mitochondrial diseases varies and depends on the proportion of mutated mitochondria in various body tissues, as well as the nature of the mutation or deletion. In order to determine how often SNHL occurs in mitochondrial diseases and what is its presenting symptom, and also whether SNHL is a marker for particular phenotypes, we carried out a review of published case reports of patients with an established diagnosis of mitochondrial disease. The review indicates that SNHL occurs at all ages and in virtually all variants of mitochondrial diseases. It is not clear whether SNHL is a marker for a more severe and more rapid course of disease; the lower prevalence of SNHL in descriptions of live patients than of those who had died may be an artifact of case selection reported in the literature. Mitochondrial disease needs to be considered in progressive hearing loss and better longitudinal audiometric study of established cases will be required to answer these questions.

Mitochondrial encephalomyopathies: clinical and molecular analysis

The classification of mitochondrial encephalomyopathies relied upon clinical, biochemical, and histological features until the discovery of mitochondrial DNA defects in 1988. Since then, an outburst of molecular genetic information has aided our understanding of the pathogenesis and the classification of these heterogeneous disorders. Novel concepts of maternal inheritance, mitochondrial DNA (mtDNA) heteroplasmy, tissue distribution, and threshold have explained many of the clinical characteristics. The discovery of point mutations, large-scale mtDNA deletions, duplications, and autosomally inherited disorders with multiple mtDNA deletions have revealed new genetic phenomena. Despite our rapidly expanding understanding of the molecular genetic defects, many questions remain to be explored to fill the gap in our knowledge of the relationship between genotype and clinical phenotype.

Extreme variability of clinical symptoms among sibs in a MELAS family correlated with heteroplasmy for the mitochondrial A3243G mutation

In a family with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes with extremely varying clinical expression, we have identified the A3243G heteroplasmic point mutation in mitochondrial DNA. The degree of severity of the clinical symptoms in the various family members was reflected in the relative quantity of mutated mitochondrial DNA in different tissues. The biochemical activity of complex I of the respiratory chain in muscle was decreased in some members of this family.

Microcompartmentation of energy metabolism at the outer mitochondrial membrane: role in diabetes mellitus and other diseases

Complexes made up of the kinases, hexokinase and glycerol kinase, together with the outer mitochondrial membrane voltage-dependent anion channel (VDAC) protein, porin, and the inner mitochondrial membrane protein, the adenine nucleotide translocator, are involved in tumorigenesis, diabetes mellitus, and central nervous system function. Identification of these two mitochondrial membrane proteins, along with an 18 kD protein, as components of the peripheral benzodiazepine receptor, provides independent confirmation of the interaction of porin and the adenine nucleotide translocator to form functional contact sites between the inner and outer mitochondrial membranes. We suggest that these are dynamic structures, with channel conductances altered by the presence of ATP, and that ligand-mediated conformational changes in the porin-adenine nucleotide translocator complexes may be a general mechanism in signal transduction.

Genetic disorders that masquerade as multiple sclerosis

There are many genetic disorders that have signs and symptoms suggestive of multiple sclerosis and that may easily be overlooked in the evaluation of both adult and pediatric multiple sclerosis patients. The recognition of a genetic disorder as the cause of a patient's "multiple sclerosis" phenotype has important implications not only for the patient, but often also for others in the patient's family who may be at risk for the same disease. We present here a review of single gene disorders that can masquerade as multiple sclerosis. For each disorder, the major clinical and biochemical characteristics are discussed, together with the appropriate testing to screen for and confirm the diagnosis. In addition, guidelines are presented for when to suspect an underlying genetic condition in a patient with a diagnosis of definite or probable multiple sclerosis. The great variety of genetic disorders that can masquerade as multiple sclerosis and the many implications of a genetic diagnosis underscore the importance of recognizing genocopies of multiple sclerosis.