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

Contribution of mitochondrial gene variants in diabetes and diabetic kidney disease

OBJECTIVES

Mitochondrial DNA (mtDNA) plays an important role in the pathogenesis of diabetes. Variants in mtDNA have been reported in diabetes, but studies on the whole mtDNA variants were limited. Our study aims to explore the association of whole mtDNA variants with diabetes and diabetic kidney disease (DKD).

METHODS

The whole mitochondrial genome was screened by next-generation sequencing in cohort 1 consisting of 50 early-onset diabetes (EOD) patients with a maternally inherited diabetes (MID) family history. A total of 42 variants possibly associated with mitochondrial diseases were identified according to the filtering strategy. These variants were sequenced in cohort 2 consisting of 90 EOD patients with MID. The association between the clinical phenotype and these variants was analyzed. Then, these variants were genotyped in cohort 3 consisting of 1,571 type 2 diabetes mellitus patients and 496 subjects with normal glucose tolerance (NGT) to analyze the association between variants with diabetes and DKD.

RESULTS

Patients with variants in the non-coding region had a higher percentage of obesity and levels of fasting insulin (62.1% vs. 24.6%, P = 0.001; 80.0% vs. 26.5% P < 0.001). The patients with the variants in rRNA had a higher prevalence of obesity (71.4% vs. 30.3%, P = 0.007), and the patients with the variants in mitochondrial complex I had a higher percentage of the upper tertile of FINS (64.3% vs. 34.3%, P = 0.049). Among 20 homogeneous variants successfully captured, two known variants (m.A3943G, m.A10005G) associated with other mitochondrial diseases were only in the diabetic group, but not in the NGT group, which perhaps indicated its possible association with diabetes. The prevalence of DKD was significantly higher in the group with the 20 variants than those without these variants (18.7% vs. 14.6%, P = 0.049) in the participants with diabetes of cohort 3.

CONCLUSION

MtDNA variants are associated with MID and DKD, and our findings advance our understanding of mtDNA in diabetes and DKD. It will have important implications for the individual therapy of mitochondrial diabetes.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clonazepam-induced liver dysfunction, severe hyperlipidaemia, and hyperglycaemic crisis: A case report

In this study, we report a case of a 50-year-old Japanese man who had chronic whiplash-associated disorder, hyperlipidaemia, hyperuricacidaemia, and mild liver dysfunction due to excessive alcohol intake. Recently, he developed mild tremor in his left hand. Initiation of clonazepam (0.5 mg once daily before bedtime) helped to gradually ameliorate the tremor. However, 13 days after clonazepam initiation, his liver function and lipid profiles aggravated, and his postprandial glucose level increased to 400 mg/dL. Clonazepam was stopped promptly, and at 7 days after discontinuation, the abnormal triglyceride levels, liver dysfunction, and glycometabolism improved without any other medical intervention. This case may provide information on cautious use of clonazepam. When clonazepam is used for patients with existing hyperlipidaemia and liver dysfunction, it may cause abnormal lipid profile, aggravate liver dysfunction, and lead to remarkable glucose elevation.

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

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

Mitochondrial disease and endocrine dysfunction

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

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.

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.

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.

Characterisation of the macular dystrophy in patients with the A3243G mitochondrial DNA point mutation with fundus autofluorescence

INTRODUCTION

The mitochondrial DNA A3243G point mutation is associated with a wide variety of systemic manifestations including a macular dystrophy. The characteristics of fundus autofluorescence (AF) in these patients are distinctive and have not been previously described.

METHODS

A complete history and ophthalmic examination, including fundus photography and autofluorescence imaging, was performed on twelve probands harbouring the A3243G point mutation.

RESULTS

Four patients had diabetes, 10/12 hearing loss, and 7/12 were visually symptomatic. A positive family history was present in 5/12. Fundus findings consisted of two primary phenotypes: discontinuous circumferentially oriented perifoveal atrophy (9/12) or an appearance consistent with pattern dystrophy (3/12). In both phenotypes pale deposits and pigment clumping were seen at the level of the retinal pigment epithelium, with occasional changes also noted outside the arcades and nasal to the optic nerve. Fundus AF imaging revealed decreased autofluorescence in areas of atrophy and increased AF of the pale subretinal deposits. In areas of the retina that appeared normal clinically, variable sized flecks of increased and decreased AF were present.

CONCLUSIONS

The mitochondrial DNA A3243G point mutation can result in disease with a variable presentation. Fundus autofluorescence reveals a recognisable phenotype in most cases that is different from other macular dystrophies.

Variation of mitochondrial gene and the association with type 2 diabetes mellitus in a Chinese population

Mitochondrial DNA (mtDNA) variants have been implicated in many diseases including diabetes mellitus. To explore whether these genetic variants contribute to the susceptibility for type 2 diabetes mellitus (T2DM) in a Chinese population, a total of 184 T2DM cases and 279 matched healthy controls were recruited. PCR restriction fragment length polymorphism (PCR-RFLP) analysis and DNA sequencing were used to determine the variants of mtDNA (including T16189C, G3316A, T3394C, A14693G, A3243G and C1310T). Some of them were further analyzed by mfold or tRNA-scan-SE software. A homoplastic A14693G, for the first time, was found in 4 of 184 Chinese cases, the frequency of A14693G and T3394C was 2.17% and 2.72%, respectively, in patients but not in the controls. Secondary structure prediction revealed that there were obvious conformational changes in T3394C mutant ND1 versus wild type and A14693G mutant tRNA(Glu) protein versus wild type, providing additional clues to the disease pathogenesis although A3243G and C1310T mutations were not detected in any patients in the two groups. The 16189 variant among type 2 diabetes was more prevalent than in controls (36.9% versus 28.7%, P=0.039), and stepwise multiple regression analysis showed that the 16189 variant was an independent factor contributing to HOMA-IR (R(2)=0.043, P=0.037). Our results suggest that the mutations of T3394C and A14693G may contribute to genetic predisposition to T2DM, with the T16189C variant being associated with insulin resistance.

Kearns Sayre syndrome: an unusual form of mitochondrial diabetes

Kearns Sayre syndrome (KSS) is a mitochondrial disorder characterized by the emergence before age 20 of progressive external ophthalmoplegia, pigmentary retinopathy, together with other heterogeneous clinical manifestations, including cardiac conduction defects, muscle abnormalities and endocrinopathies. KSS is associated with large heteroplasmic deletions in mitochondrial DNA. We report the case of a 43-year-old woman, with diabetes mellitus as a first manifestation at age 19. Later, she exhibited bilateral ptosis and external ophthalmoplegia with progressive worsening. DNA analysis identified a large mitochondrial DNA (mtDNA) deletion, which confirmed the diagnosis of KSS. By reporting this case with diabetes mellitus as first manifestation, we aim at emphasizing problems of diagnosis in these subtypes of mitochondrial diabetes.

Involvement of mtDNA damage in free fatty acid-induced apoptosis

A growing body of evidence indicates that free fatty acids (FFA) can have deleterious effects on beta-cells. It has been suggested that the beta-cell dysfunction and death observed in diabetes may involve exaggerated activation of the inducible form of nitric oxide synthase (iNOS) by FFA, with the resultant generation of excess nitric oxide (NO). However, the cellular targets with which NO interact have not been fully identified. We hypothesized that one of these targets might be mitochondrial DNA (mtDNA). Therefore, experiments were initiated to evaluate damage to mtDNA caused by exposure of INS-1 cells to FFA (2/1 oleate/palmetate). The results showed that FFA caused a dose-dependent increase in mtDNA damage. Additionally, using ligation-mediated PCR, we were able to show that the DNA damage pattern at the nucleotide level was identical to the one induced by pure NO and different from damage caused by peroxynitrite or superoxide. Following exposure to FFA, apoptosis was detected by DAPI staining and cytochrome c release. Treatment of INS-1 cells with the iNOS inhibitor aminoguanidine protected these cells from mtDNA damage and diminished the appearance of apoptosis. These studies suggest that mtDNA may be a sensitive target for NO-induced toxicity which may provoke apoptosis in beta-cells following exposure to FFA.

Heterogeneity of diabetes phenotype in patients with 3243 bp mutation of mitochondrial DNA (Maternally Inherited Diabetes and Deafness or MIDD)

OBJECTIVE

In patients with maternally inherited diabetes and deafness (MIDD), due to 3 243 A > G mutation of mitochondrial DNA (mtDNA), diabetes may present with variable phenotypes.

OBJECTIVE

To ascertain the existence of two distinct phenotypes, MIDD1 and MIDD2, in a series of patients with MIDD.

DESIGN

Multicenter prospective study.

PATIENTS

77 patients with diabetes and the mtDNA 3243 mutation and 139 control patients with type 1 (T1D) or type 2 (T2D) diabetes, matched according to initial presentation of diabetes, age at onset, sex, and duration of diabetes (24 T1D and 115 T2D, including 55 treated with insulin).

MEASUREMENTS

Anthropometric characteristics (height, body weight, body mass index [BMI], sex), family history of diabetes, and characteristics of diabetes (age at onset, treatment, hemoglobin A1c [HbA1c]), extrapancreatic manifestations.

RESULTS

In 13 cases (17%, MIDD1), diabetes presented as insulin-dependent from the onset, with ketoacidosis in 6 cases. In 64 cases (83%, MIDD2), diabetes resembled T2D, and was treated with diet in 12 cases, oral hypoglycemic agents in 21 cases, or insulin in 31 cases. Compared with patients with MIDD2, patients with MIDD1 were characterized by lower age at onset of first manifestation of MIDD (25.4 +/- 9.6 vs 33.7 +/- 13.2 Years, P<0.0005), lower body weight (49.1 +/- 7.4 vs 56.3 +/- 10.9 kg, P<0.0025), lower BMI (18.2 +/- 2.3 vs 20.9 +/- 3.6 kg/m2, P<0.0005), and higher HbA1c levels (9.5 +/- 2.0 vs 7.5 +/- 1.6%, P<0.0005). Frequency of family history of diabetes and of extrapancreatic manifestations was the same in both MIDD subtypes. No difference was found within the MIDD2 subtype when comparing patients treated with or without insulin. Compared with matched controls, patients with MIDD had a lower BMI (MIDD1/T1D 18.2 +/- 2.3 vs 24.0 +/- 3.6 kg/m2 and MIDD2/T2D 20.9 +/- 3.6 vs 30.2 +/- 5.9 kg/m2, P<0.0025). Lastly, male patients with MIDD had a shorter height than controls (MIDD1/T1D: 166.1 +/- 3.2 vs 177.3 +/- 6.6 cm and MIDD2/T2D: 168.4 +/- 7.2 vs 173.6 +/- 6.6 cm P<0.025).

CONCLUSIONS

These results confirm the existence of two different phenotypes in MIDD, MIDD1 and MIDD2, which may be related to the severity of the mitochondrial disease. The role of other genetic and/or environmental factors in the variable phenotype of MIDD remains to be elucidated.

Prevalence of the mitochondrial DNA A1555G mutation in sensorineural deafness patients in island Southeast Asia

A mtDNA A1555G base substitution in a highly conserved region of the 12S rRNA gene has been reported to be the main cause of aminoglycoside induced deafness. This mutation is found in approximately 3% of Japanese and 0.5-2.4% of European sensorineural deafness patients. We report a high prevalence (5.3%) of the A1555G mutation in sensorineural deafness patients in Sulawesi (Indonesia). Our result confirms the importance of determining the prevalence of the mtDNA A1555G mutation in different populations, and the need for mutation detection before the administration of aminoglycoside antibiotics.

Molecular analysis of diabetes mellitus-associated A3243G mitochondrial DNA mutation in Taiwanese cases

Investigation of the clinical manifestations of MELAS-specific A3243G mitochondrial DNA (mtDNA) point mutation has suggested that the A3243G mutation of mtDNA can cause certain subtypes of diabetes mellitus (DM) and contributes about 0.15% of the overall incidence of diabetes. However, a relationship between the diabetic syndrome and the proportion of mutant mtDNA in affected tissues remains unclear. In this article, we report the results of our investigation of 14 diabetic and 23 non-diabetic patients who had the A3243G mutant mtDNA. The proportions of mutant mtDNA in different tissues were noted to change variably and neither heteroplasmy of mutant mtDNA in various tissues nor the proportion of mutated mtDNA in a specific tissue showed a correlation with the clinical phenotype of DM. Generation of a diabetic syndrome was not predictable from either the content of mutant mtDNA in leukocytes, hair follicles, or in muscle tissues. Further study showed that muscle tissue has the highest proportion of mutant mtDNA followed by hair follicles and by blood cells. Moreover, we observed that as the patient's age increased, all tissue showed a declining proportion of mutant mtDNA. These findings suggest that age may play a role in the manifestation of diabetes in patients with A3243G mutation of mtDNA.

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.

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.

Molecular and histological evaluation of pancreata from patients with a mitochondrial gene mutation associated with impaired insulin secretion

A mutation in mitochondrial DNA, which was originally identified in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), can be associated with a subtype of diabetes mellitus. To determine the molecular and histological basis of impaired insulin secretion in the subjects with this mutation, we studied autopsy pancreata specimens from eight subjects diagnosed as having MELAS. The 3243 bp mutation was identified in seven out of eight pancreata examined. Immunohistochemical studies demonstrated a reduction in total islet mass, and in the numbers of both B and A cells. No evidence of insulitis or apoptosis was found. These data suggested that the 3243 bp mutation may cause the reduction of islet cells, mainly through mechanisms other than autoimmune destruction.

Maternally transmitted susceptibility to non-insulin-dependent diabetes mellitus and left ventricular hypertrophy

OBJECTIVES

We studied the association of diabetes transmission with left ventricular hypertrophy (LVH) in patients with non-insulin-dependent diabetes mellitus (NIDDM).

BACKGROUND

It is suggested that NIDDM has a strong genetic basis and that maternally transmitted NIDDM is associated with mitochondrial deoxyribonucleic acid (DNA) mutations. However, genetic factors for LVH in NIDDM are unknown.

METHODS

We investigated the family history of diabetes and the prevalence of LVH using electrocardiography in 834 patients with NIDDM, of whom 199 also underwent echocardiography.

RESULTS

Of the 834 patients, 121 had diabetic mothers, 122 had diabetic fathers and 30 had both. The LVH criterion of S(v1) + R(V5) or R(v6) >35 mm was met in 148 patients. The percentage of patients having diabetic mothers was higher in those with LVH criterion (29%) than without it (16%) (p < 0.001), but the percentage of patients having diabetic fathers was similar in those with LVH (18%) and without it (18%). Compared with the 683 patients with nondiabetic mothers, the 151 patients with diabetic mothers were younger and had earlier onset of diabetes. The percentage of patients having diabetic siblings was also higher in those with diabetic mothers (31%) than in those with nondiabetic mothers (18%) (p < 0.001). On electrocardiograms, the prevalence of LVH was higher in patients with diabetic mothers (28%) than in those with nondiabetic mothers (15%) (p < 0.001). Echocardiograms showed that patients with diabetic mothers had greater left ventricular wall thickness and mass than those with nondiabetic mothers. In multivariate analysis, the family history of diabetes in mothers was an independent factor to LVH, but the family history of diabetes in fathers was not.

CONCLUSIONS

Maternal transmission of diabetes was associated with LVH in patients with NIDDM. Some genetic factors of diabetes, such as mitochondrial DNA abnormalities, may contribute to the development of LVH in maternally transmitted NIDDM.

Early onset of diabetes mellitus associated with the mitochondrial DNA T14709C point mutation: patient report and literature review

We report a family in which a mother and son were affected with diabetes mellitus and myopathy characterized by ragged red fibers and suggestive of mitochondrial disease. Mitochondrial DNA (mtDNA) analysis of DNA isolated from peripheral blood showed a T-->C point mutation at nucleotide position 14709, in the transfer RNA gene for glutamic acid. We review the association of diabetes and mtDNA mutations. This child's case is unusual because of the early onset of diabetes, which is more typical of mtDNA deletions.

Decreased mitochondrial DNA content in peripheral blood precedes the development of non-insulin-dependent diabetes mellitus

Qualitative changes in mitochondrial DNA (mtDNA), such as mutations and deletions, have been implicated in the pathogenesis of diabetes mellitus. In addition to the qualitative changes, mtDNA is subject to quantitative changes, and is vulnerable to oxidative stress, resulting in both qualitative and quantitative changes. This study was performed to investigate whether quantitative changes in mtDNA occur in non-insulin-dependent diabetes mellitus (NIDDM) patients and also in pre-diabetic subjects. MtDNA content from peripheral blood was measured by slot-blot analysis in 55 NIDDM patients and 29 age- and sex-matched control subjects. We have also analysed the mtDNA copies by quantitative polymerase chain reaction (PCR) method in 23 pre-diabetic subjects who converted to diabetic in 2 years and 22 age- and sex-matched control subjects who remained non-diabetic. Mean mtDNA quantity measured by slot blot method was 35% lower in patients with NIDDM than in control subjects (12.3+/-8.1 vs. 19.1+/-8.2 AU/microg DNA; P < 0.05). MtDNA quantities did not correlate with age, body mass index, duration of diabetes or HbA1c levels. We have also found that the mtDNA copies in subjects who converted to diabetes in 2 years were lower than in controls even before the development of diabetes (102.8+/-41.5 vs. 137.8+/-67.7 copies/pg template DNA P < 0.05). Inverse correlations were noted between mtDNA content and baseline waist hip circumference ratio (WHR) (r = -0.31, P < 0.05), and fasting glucose level (r = - 0.35, P < 0.05), diastolic blood pressure (r = -0.36, P < 0.05), and WHR (r = -0.40, P < 0.01) after development of diabetes. In conclusion, we demonstrate that the content of mtDNA decreases in peripheral blood of patients with NIDDM and the lower mtDNA levels precede the development of diabetes.

Diabetes mellitus associated with the 3243 mitochondrial tRNA(Leu)(UUR) mutation: insulin secretion and sensitivity

To investigate the pathophysiology of diabetes mellitus associated with the 3243 mitochondrial tRNA(Leu)(UUR) mutation (DM-Mt3243), insulin secretion and sensitivity were studied using the 75-g oral glucose tolerance test (oGTT), 1-mg intravenous glucagon test, and euglycemic glucose clamp test. Twelve DM-Mt3243 patients were investigated (seven men and five women). Their ages ranged from 36 to 74 years, and the onset of diabetes occurred at 44.5 +/- 9.5 years (mean +/- SD). In the glucose tolerance test, nine patients (75.0%) showed lower C-peptide reactivity (CPR) than normal at 30 minutes, suggesting blunted insulin secretion. Three patients showed an impaired glucose tolerance (IGT) pattern, although they had absolute hyperglycemia at the onset of diabetes. In the glucagon test, 10 patients (76.3%) had CPR within the normal range at 6 minutes, indicating an adequate response. In the glucose clamp test, the M value was 8.70 +/- 2.35 mg/kg/min and was within normal limits in all patients. The glucose metabolized (M value) was negatively correlated with 24-hour urinary C-peptide excretion (r = .696, P < .05). Thus, plasma CPR to glucose loading was blunted in many DM-Mt3243 patients, but CPR to glucagon was relatively well preserved. This difference in the intrinsic insulin response to the two stimuli may be characteristic of DM-Mt3243. Although M values were normal in all subjects, the correlation with 24-hour urinary C-peptide excretion suggests a relationship between insulin sensitivity and insulin secretion. These two mechanisms may cooperate to maintain homeostasis in this disease. Since three patients did not progress with aging, this mutation may not always cause gradual beta-cell destruction.

High prevalence of mitochondrial diabetes mellitus in Japanese patients with major risk factors

To identify diabetes mellitus caused by the mitochondrial gene substitution at genomic nucleotide pair 3243 (M3243A-->G) we selected 87 diabetic patients with high risk factors such as maternal inheritance and hearing loss. Total DNA was extracted from peripheral leukocytes, and mitochondrial DNA fragments containing M3243A-->G were amplified by polymerase chain reaction (PCR). The amplified fragments were digested with a restriction endonuclease Apa1 and analyzed by agarose gel electrophoresis. The incidence of the M3243A-->G mutation was 4.6% (four of 87) in diabetic patients with maternal inheritance and/or hearing loss. In a subgroup with both maternal inheritance and hearing loss, the incidence of the mutation was as high as 21.4% (three of 14). Cardiac disorders were also present in all four diabetic patients with the mutation. This study suggests that maternal inheritance and hearing loss are useful clinical findings to identify diabetic patients with the mutation, and that cardiac involvement is a high risk factor for the M3243A-->G mutation.

Gestational diabetes mellitus and gene mutations which affect insulin secretion

We investigated whether genetic mutations known to impair insulin secretion and glucose tolerance are operative in a group of American women with gestational diabetes mellitus. Study groups were comprised of elderly non-diabetic controls (n = 55) with normal glucose tolerance and patients with gestational diabetes (n = 50), together with one family with maturity-onset diabetes of the young (three controls and three affected). No mutations were detected in any exon of the human glucokinase gene or the mitochondrial tRNA[Leu](UUR) gene by single strand conformational analysis and direct exon sequencing. Also, chi2 analysis showed no significant association with gestational diabetes for a polymorphism at position -30 (G --> A) of the beta-cell-specific glucokinase gene promoter. We have determined that glucokinase and mitochondrial tRNA[Leu](UUR) gene mutations, which are known to impair insulin secretion are relatively uncommon and do not constitute a large component of genetic risk for gestational diabetes in the study population.

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.

Nephropathy and growth hormone deficiency in a patient with mitochondrial tRNA(Leu(UUR)) mutation

A mitochondrial A 3243 G mutation in the tRNA(Leu(UUR)) gene was first described as a common cause of MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like syndrome). This same mutation is also the cause of a totally different disorder, a subtype of diabetes mellitus which is inherited maternally and often associated with sensorineural hearing loss. In this paper, we report on a Japanese boy with A 3243 G who developed a previously undescribed combination of symptoms, nephropathy and growth hormone deficiency. The patient first presented with short stature and moderate mental retardation. Growth hormone (GH) provocation tests showed deficient growth hormone secretion. During the course of follow up, he presented with progressive nephropathy followed by the development of diabetes mellitus. The results of laboratory tests and renal biopsy were against incidental association of known types of nephropathy. On PCR-RFLP analysis, the percentage of mutated mtDNA was higher in the renal biopsy specimen than 12 peripheral blood leucocytes. Our case suggests that mitochondrial diseases should be taken into account when there is nephropathy of unknown cause. In addition, the presence of growth hormone deficiency may account for part of the mechanism leading to short stature commonly seen in these patients.

Maternally inherited diabetes and deafness: a new diabetes subtype

Diabetes mellitus is a common disease with many forms of clinical expression. In addition, the development of diabetic complications is not only dependent on glycaemic control but also on individual factors which may be related to genetic heterogeneity. At present, multiple genetic factors are being recognized as contributing to the development of diabetes or possibly modulating its clinical expression. The purpose of this review is to give an overview of our current knowledge on a subtype of diabetes which is apparently caused by a single mutation in the mitochondrial DNA.

Effect of 14 days' subcutaneous administration of the human amylin analogue, pramlintide (AC137), on an intravenous insulin challenge and response to a standard liquid meal in patients with IDDM

Individuals with insulin-dependent diabetes mellitus (IDDM or type 1 diabetes) are deficient in both insulin and amylin, peptides secreted by the beta cell. We have investigated the effects of amylin replacement therapy employing the human amylin analogue, pramlintide (25, 28, 29-pro-human amylin, previously referred to as AC137), upon the responses to a standardized insulin infusion (40 mU. kg-1. h-1) for 100 min and a liquid Sustacal meal (360 kcal) in 84 healthy IDDM patients. Following baseline evaluations, patients were randomly assigned to receive subcutaneous injections of placebo, 30, 100 or 300 micrograms pramlintide 30 min before meals for 14 days. There was no meaningful difference between adverse events reported by the 30-micrograms pramlintide and the placebo groups, but ten subjects withdrew due to nausea, eight of these in the 300-micrograms dose group. Peak plasma pramlintide concentrations for the 30-micrograms group were 21 +/- 3 and 29 +/- 5 pmol/l on Days 1 and 14, respectively. These values are similar to postprandial plasma amylin concentrations in normal volunteers. The plasma glucose, free insulin, glucagon, epinephrine and norepinephrine concentrations during the insulin infusion test before and after therapy were identical in each of the group. Prior to pramlintide therapy, Sustacal ingestion produced a 4.0-4.8 mmol/l rise in plasma glucose concentrations in each of the groups. Pramlintide therapy reduced postprandial hyperglycaemia as reflected by the 3-h incremental AUCglucose (AUCglucose above or below fasting glucose concentration) Day 1 vs Day 14: 30 micrograms, 322 +/- 92 vs -38 +/- 161 mmol/l.min, p = 0.010; 100 micrograms, 317 +/- 92 vs -39 +/- 76 mmol/l.min, p = 0.001; and 300 micrograms, 268 +/- 96 vs -245 +/- 189 mmol/l.min, p = 0.077. Thus, pramlintide therapy with these regimens did not appear to impair either in vivo insulin action or the counter-regulatory response to hypoglycaemia but did show a clear effect of blunting postprandial hyperglycaemia following a standardized meal.