A cross-sectional study for glucose intolerance of myotonic dystrophy

Skeletal muscle disorders as risk factors for type 2 diabetes

The incidence and prevalence of muscular disorders and of type 2 diabetes (T2D) is increasing and both represent highly significant healthcare problems, both economically and compromising quality of life. Interestingly, skeletal muscle dysfunction and T2D share some commonalities including dysregulated glucose homeostasis, increased oxidative stress, dyslipidemia, and cytokine alterations. Several lines of evidence have hinted to a relationship between skeletal muscle dysfunction and T2D. For instance, T2D affects skeletal muscle morphology, functionality, and overall health through altered protein metabolism, impaired mitochondrial function, and ultimately cell viability. Conversely, humans suffering from myopathies and their experimental models demonstrated increased incidence of T2D through altered muscle glucose disposal function due to abnormal calcium homeostasis, compromised mitochondrial function, dyslipidemia, increased inflammatory cytokines and fiber size alterations and disproportions. Lifestyle modifications are essential for improving and maintaining mobility and metabolic health in individuals suffering from myopathies along with T2D. In this review, we updated current literature evidence on clinical incidence of T2D in inflammatory, mitochondrial, metabolic myopathies, and muscular dystrophies and further discussed the molecular basis of these skeletal muscle disorders leading to T2D.

Investigation of Glucose Metabolism by Continuous Glucose Monitoring and Validation of Dipeptidyl Peptidase 4 Inhibitor Use in Patients with Myotonic Dystrophy Type 1

Objectives: We characterized blood glucose fluctuations in patients with myotonic dystrophy type 1 (DM1). After confirming the incretin secretion capacity of patients with DM1, we intended to clarify whether dipeptidyl peptidase 4 (DPP-4) inhibitor administration was appropriate in cases of DM1 with diabetes mellitus. Methods: A 48 h continuous glucose monitoring (CGM) was performed in 29 Japanese patients with DM1. An oral glucose tolerance test (OGTT) was performed in patients with DM1 and five disease controls, and levels of blood glucose, insulin, and incretin (glucagon-like peptide-1 and gastric inhibitory polypeptide) were measured. DPP-4 inhibitors were administered to patients with diabetes mellitus complicated by DM1, and the CGM results were compared. Results: The CGM showed distinct patterns of blood glucose variability among patients classified by an OGTT pattern with significant differences in glucose parameters such as time above 140 mg/dL and mean amplitude of glycemic excursions between the groups. High sensor glucose values were observed in a certain number of patients who were classified as having normal or impaired glucose tolerance by the OGTT. The CGM confirmed the presence of low glucose levels in several patients. Incretin secretion, the target of DPP-4 inhibitors, was preserved in patients with DM1. DPP-4 inhibitor treatment resulted in lower glucose levels and improved insulin secretion in some patients. Conclusions: This is the first CGM study for DM1 patients. The CGM identified potential early abnormalities in glucose metabolism in DM1. In the future, it will be crucial to explore effective methods for harnessing CGM and assessing it quantitatively in DM1.

Dyslipidemia in Muscular Dystrophy: A Systematic Review and Meta-Analysis

BACKGROUND

Muscular dystrophies (MDs) are characterized by chronic muscle wasting but also poorly understood metabolic co-morbidities. We have recently shown that Duchenne MD (DMD) patients, dogs and asymptomatic carriers are affected by a new form of dyslipidemia that may exacerbate muscle damage.

OBJECTIVE

We aimed to perform a systematic review and meta-analysis for evidence that other types of MDs are associated with dyslipidemia compared to healthy controls.

METHODS

Search was conducted using MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials for reports that compare plasma/serum lipids from MD patients and controls, and meta-analysis of cross-sectional studies quantifying total cholesterol, high-density lipoprotein, low density lipoprotein and triglycerides was performed.

RESULTS

Out of 749 studies, 17 met our inclusion criteria for meta-analysis. 14 of the 17 studies (82% ) included investigated myotonic dystrophy (DM); other studies were on pseudohypertrophic MD (PMD) or DMD. As a whole, MD individuals had significantly higher levels of circulating total cholesterol (Hedges' g with 95% confidence interval [CI], 0.80 [0.03 - 1.56]; p = 0.04) and triglycerides (Hedges' g with 95% confidence interval [CI], 2.28[0.63 - 3.92]; p = 0.01) compared to controls. Meta-regression analysis showed the percentage of male gender was significantly associated with the difference in total cholesterol (beta = 0.05; 95% CI, - 0.02 to 0.11; p = 0.043) and high-density lipoprotein (beta = - 9.38; 95% CI, - 16.26 to - 2.50; p = 0.028).

CONCLUSIONS

MD is associated with significantly higher circulating levels of total cholesterol and triglycerides. However, caution on the interpretation of these findings is warranted and future longitudinal research is required to better understand this relationship.

Vorinostat Improves Myotonic Dystrophy Type 1 Splicing Abnormalities in DM1 Muscle Cell Lines and Skeletal Muscle from a DM1 Mouse Model

Myotonic dystrophy type 1 (DM1), the most common form of adult muscular dystrophy, is caused by an abnormal expansion of CTG repeats in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene. The expanded repeats of the DMPK mRNA form hairpin structures in vitro, which cause misregulation and/or sequestration of proteins including the splicing regulator muscleblind-like 1 (MBNL1). In turn, misregulation and sequestration of such proteins result in the aberrant alternative splicing of diverse mRNAs and underlie, at least in part, DM1 pathogenesis. It has been previously shown that disaggregating RNA foci repletes free MBNL1, rescues DM1 spliceopathy, and alleviates associated symptoms such as myotonia. Using an FDA-approved drug library, we have screened for a reduction of CUG foci in patient muscle cells and identified the HDAC inhibitor, vorinostat, as an inhibitor of foci formation; SERCA1 (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) spliceopathy was also improved by vorinostat treatment. Vorinostat treatment in a mouse model of DM1 (human skeletal actin-long repeat; HSALR) improved several spliceopathies, reduced muscle central nucleation, and restored chloride channel levels at the sarcolemma. Our in vitro and in vivo evidence showing amelioration of several DM1 disease markers marks vorinostat as a promising novel DM1 therapy.

Targeting Myotonic Dystrophy Type 1 with Metformin

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder of genetic origin. Progressive muscular weakness, atrophy and myotonia are its most prominent neuromuscular features, while additional clinical manifestations in multiple organs are also common. Overall, DM1 features resemble accelerated aging. There is currently no cure or specific treatment for myotonic dystrophy patients. However, in recent years a great effort has been made to identify potential new therapeutic strategies for DM1 patients. Metformin is a biguanide antidiabetic drug, with potential to delay aging at cellular and organismal levels. In DM1, different studies revealed that metformin rescues multiple phenotypes of the disease. This review provides an overview of recent findings describing metformin as a novel therapy to combat DM1 and their link with aging.

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

Metabolic complications in myotonic dystrophy type 1: A cross-sectional survey using the National Registry of Japan

Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy in adults, affecting multiple organs, including the eyes, heart, endocrine system, and central nervous system. The broad spectrum of DM1 symptoms has been attributed to the aberrant pre-mRNA splicing of various genes due to an abnormal expansion of the CTG repeat in the 3' untranslated region of the DMPK gene. The current challenge in the clinical care of DM1 is the lack of well-established protocols for the management of each organ disorder or symptom. Moreover, the current status of clinical management has not been adequately explored. Metabolic disturbance in DM1 has been less explored among the DM1 manifestations, even though impaired glucose tolerance is a widely known metabolic disorder associated with DM1. We investigated the metabolic disturbance related to DM1 using the national registry of neuromuscular diseases in Japan, Registry of Muscular Dystrophy (Remudy), and assessed the metabolic complications in DM1 and the current treatments. We obtained comprehensive information on the current status of liver dysfunction and dyslipidemia in a sizeable DM1 cohort (~300). We confirmed that the incidence of liver dysfunction and dyslipidemia, particularly hypertriglyceridemia, as well as impaired glucose tolerance, were significantly higher in DM1 patients. Furthermore, the majority of DM1 patients with dyslipidemia were not receiving pharmacotherapy. Our data highlight the current status of DM1 patients in Japan, which can guide the establishment of the standard of care for metabolic issues consequent to DM1.

Metabolic Alterations in Myotonic Dystrophy Type 1 and Their Correlation with Lipin

Myotonic dystrophy type 1 (DM1) is an autosomal dominant hereditary and multisystemic disease, characterized by progressive distal muscle weakness and myotonia. Despite huge efforts, the pathophysiological mechanisms underlying DM1 remain elusive. In this review, the metabolic alterations observed in patients with DM1 and their connection with lipin proteins are discussed. We start by briefly describing the epidemiology, the physiopathological and systemic features of DM1. The molecular mechanisms proposed for DM1 are explored and summarized. An overview of metabolic syndrome, dyslipidemia, and the summary of metabolic alterations observed in patients with DM1 are presented. Patients with DM1 present clinical evidence of metabolic alterations, namely increased levels of triacylglycerol and low-density lipoprotein, increased insulin and glucose levels, increased abdominal obesity, and low levels of high-density lipoprotein. These metabolic alterations may be associated with lipins, which are phosphatidate phosphatase enzymes that regulates the triacylglycerol levels, phospholipids, lipid signaling pathways, and are transcriptional co-activators. Furthermore, lipins are also important for autophagy, inflammasome activation and lipoproteins synthesis. We demonstrate the association of lipin with the metabolic alterations in patients with DM1, which supports further clinical studies and a proper exploration of lipin proteins as therapeutic targets for metabolic syndrome, which is important for controlling many diseases including DM1.

Hormonal and metabolic gender differences in a cohort of myotonic dystrophy type 1 subjects: a retrospective, case-control study

PURPOSE

Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by CTG expansion in the DMPK gene. The aim was to investigate the endocrine and metabolic aspects of DM1.

PATIENTS AND METHODS

Retrospective, case-control study. We compared pituitary, thyroid, adrenal, gonadal and liver function and glycolipid metabolism of 63 DM1 patients against 100 control subjects. Given age-related differences, 2 further subgroups were created to investigate the pituitary-gonadal axis: < 41 (1a) and ≥ 41 (1b) years old for male subjects and < 46 (2a) and ≥ 46 (2b) years old for female subjects. Testicular and thyroid ultrasounds were also performed in the DM1 group.

RESULTS

FT3 and FT4 were significantly lower in DM1 men than controls, while for both males and females, thyroglobulin, ACTH and cortisol were significantly higher in the DM1 group. Gonadotropin levels were significantly higher and inhibin B and DHEA-S levels significantly lower in DM1 patients than controls for both male subgroups. Testosterone and SHBG were significantly higher in controls than in patients for subgroup 1a. Prolactin was significantly higher in patients in subgroups 1b, while testosterone was lower in subgroup 2a than in age-matched female controls. A correlation between the number of CTG repeats and the percentage of male hypogonadal subjects was found. Finally, there was a worse glucose and lipid pattern and significantly higher transaminase and gamma-GT levels in both male and female patients.

CONCLUSIONS

The high frequency of endocrine and metabolic abnormalities in DM1 highlights the importance of endocrine monitoring to enable the prompt initiation of a suitable therapy.

A signaling hub of insulin receptor, dystrophin glycoprotein complex and plakoglobin regulates muscle size

Signaling through the insulin receptor governs central physiological functions related to cell growth and metabolism. Here we show by tandem native protein complex purification approach and super-resolution STED microscopy that insulin receptor activity requires association with the fundamental structural module in muscle, the dystrophin glycoprotein complex (DGC), and the desmosomal component plakoglobin (γ-catenin). The integrity of this high-molecular-mass assembly renders skeletal muscle susceptibility to insulin, because DGC-insulin receptor dissociation by plakoglobin downregulation reduces insulin signaling and causes atrophy. Furthermore, low insulin receptor activity in muscles from transgenic or fasted mice decreases plakoglobin-DGC-insulin receptor content on the plasma membrane, but not when plakoglobin is overexpressed. By masking β-dystroglycan LIR domains, plakoglobin prevents autophagic clearance of plakoglobin-DGC-insulin receptor co-assemblies and maintains their function. Our findings establish DGC as a signaling hub, and provide a possible mechanism for the insulin resistance in Duchenne Muscular Dystrophy, and for the cardiomyopathies seen with plakoglobin mutations.

Insulin Signaling as a Key Moderator in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic disease characterized by multi-system involvement. Affected organ system includes skeletal muscle, heart, gastro-intestinal system and the brain. In this review, we evaluate the evidence for alterations in insulin signaling and their relation to clinical DM1 features. We start by summarizing the molecular pathophysiology of DM1. Next, an overview of normal insulin signaling physiology is given, and evidence for alterations herein in DM1 is presented. Clinically, evidence for involvement of insulin signaling pathways in DM1 is based on the increased incidence of insulin resistance seen in clinical practice and recent trial evidence of beneficial effects of metformin on muscle function. Indirectly, further support may be derived from certain CNS derived symptoms characteristic of DM1, such as obsessive-compulsive behavior features, for which links with altered insulin signaling has been demonstrated in other diseases. At the basic scientific level, several pathophysiological mechanisms that operate in DM1 may compromise normal insulin signaling physiology. The evidence presented here reflects the importance of insulin signaling in relation to clinical features of DM1 and justifies further basic scientific and clinical, therapeutically oriented research.

Adiponectin, a unique adipocyte-derived factor beyond hormones

Visceral fat accumulation has a marked impact on atherosclerotic cardiovascular diseases and metabolic syndrome clustering diabetes, dyslipidemia, and hypertension. Adiponectin, an adipocyte-derived circulating protein, is a representative adipocytokine and uniquely possesses two major properties: 1) its circulating concentration is approximately 3-6 orders of magnitude greater than ordinary hormones and cytokines; 2) its concentration inversely correlates with body fat mass despite its adipocyte-specific production. Low serum levels of adiponectin correlate with cardiometabolic diseases. Extensive experimental evidence has demonstrated that adiponectin possesses multiple properties, such as anti-atherosclerotic, anti-diabetic, and anti-inflammatory activities. It has been shown to play a central role against the development of metabolic syndrome and its complications. However, even approximately 25 years after its discovery, the properties of adiponectin, including how and why it exerts multiple beneficial effects on various tissues and/or organs, remain unclear. Furthermore, the mechanisms responsible for the very high circulating concentrations of adiponectin in the bloodstream have not been elucidated. Several adiponectin-binding partners, such as AdipoR1/2, have been identified, but do not fully explain the multi-functional and beneficial properties of adiponectin. Recent advances in adiponectin research may resolve these issues. Adiponectin binds to and covers cell surfaces with T-cadherin, a unique glycosylphosphatidylinositol (GPI)-anchored cadherin. The adiponectin/T-cadherin complex enhances exosomal production and release, excreting cell-toxic products from cells, particularly in the vasculature. In this review, we discuss adiponectin and the role of the adiponectin/T-cadherin system in the maintenance of whole body homeostasis and cardiovascular protection.

Core Clinical Phenotypes in Myotonic Dystrophies

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) represent the most frequent multisystemic muscular dystrophies in adulthood. They are progressive, autosomal dominant diseases caused by an abnormal expansion of an unstable nucleotide repeat located in the non-coding region of their respective genes DMPK for DM1 and CNBP in DM2. Clinically, these multisystemic disorders are characterized by a high variability of muscular and extramuscular symptoms, often causing a delay in diagnosis. For both subtypes, many symptoms overlap, but some differences allow their clinical distinction. This article highlights the clinical core features of myotonic dystrophies, thus facilitating their early recognition and diagnosis. Particular attention will be given to signs and symptoms of muscular involvement, to issues related to respiratory impairment, and to the multiorgan involvement. This article is part of a Special Issue entitled “Beyond Borders: Myotonic Dystrophies—A European Perception.”

Elevated plasma levels of cardiac troponin-I predict left ventricular systolic dysfunction in patients with myotonic dystrophy type 1: A multicentre cohort follow-up study

Objective

High sensitivity plasma cardiac troponin-I (cTnI) is emerging as a strong predictor of cardiac events in a variety of settings. We have explored its utility in patients with myotonic dystrophy type 1 (DM1).

Methods

117 patients with DM1 were recruited from routine outpatient clinics across three health boards. A single measurement of cTnI was made using the ARCHITECT STAT Troponin I assay. Demographic, ECG, echocardiographic and other clinical data were obtained from electronic medical records. Follow up was for a mean of 23 months.

Results

Fifty five females and 62 males (mean age 47.7 years) were included. Complete data were available for ECG in 107, echocardiography in 53. Muscle Impairment Rating Scale score was recorded for all patients. A highly significant excess (p = 0.0007) of DM1 patients presented with cTnI levels greater than the 99^th centile of the range usually observed in the general population (9 patients; 7.6%). Three patients with elevated troponin were found to have left ventricular systolic dysfunction (LVSD), compared with four of those with normal range cTnI (33.3% versus 3.7%; p = 0.001). Sixty two patients had a cTnI level < 5ng/L, of whom only one had documented evidence of LVSD. Elevated cTnI was not predictive of severe conduction abnormalities on ECG, or presence of a cardiac device, nor did cTnI level correlate with muscle strength expressed by Muscle Impairment Rating Scale score.

Conclusions

Plasma cTnI is highly elevated in some ambulatory patients with DM1 and shows promise as a tool to aid cardiac risk stratification, possibly by detecting myocardial involvement. Further studies with larger patient numbers are warranted to assess its utility in this setting.

Metabolic syndrome in patients with myotonic dystrophy type 1

INTRODUCTION

The aim of this study was to assess the frequency and features of metabolic syndrome (MetS) in myotonic dystrophy type 1 (DM1).

METHODS

We studied 66 DM1 patients (50% men, aged 41.9 ± 10.5 years, disease duration of 19.3 ± 8.6 years). New worldwide consensus criteria for MetS from 2009 were used.

RESULTS

Components of MetS were present at the following frequencies: hypertriglyceridemia 67%; low HDL cholesterol 35%; hypertension 18%; central obesity 14%; and hyperglycemia 9%. MetS was present in 11 (17%) patients. The presence of MetS was not associated with patients' gender, age, disease severity, disease duration, or CTG repeat length (P > 0.05). Patients with MetS had significantly lower total SF-36 scores as a measure of quality of life in comparison to patients without MetS (P < 0.05).

CONCLUSION

Although certain components of MetS were very frequent in patients with DM1, only 17% met the criteria for MetS.

Endocrine function over time in patients with myotonic dystrophy type 1

BACKGROUND AND PURPOSE

Patients with myotonic dystrophy type 1 (DM1) have an increased incidence of endocrine dysfunction. In this study, the temporal evolution of endocrine dysfunction in patients with DM1 was investigated.

METHODS

Endocrine function was assessed in 68 patients with DM1, in whom endocrine function had been followed, on average, for 8 years. The endocrine function was assessed by measuring the concentration of hormones and metabolites in blood and by validating libido with questionnaires.

RESULTS

At baseline, 30 of the 68 patients presented with at least one hormonal dysfunction. When re-evaluated after 8 years, 57 of 68 patients had endocrine dysfunction. Diabetic patients had increased from one to four. At follow-up, hyperparathyroidism occurred in 25% and abnormal thyroid-stimulating hormone in 21%, compared with 14% and 9% at baseline. Sixteen of 33 men had increased luteinizing hormone levels compared with seven at baseline.

CONCLUSIONS

Our findings show that endocrine abnormalities amongst patients with DM1 increase over time. Based on these findings it is suggested that correctable endocrine abnormalities should be monitored periodically in this patient group.

Dysfunctional muscle and liver glycogen metabolism in mdx dystrophic mice

Background

Duchenne muscular dystrophy (DMD) is a severe, genetic muscle wasting disorder characterised by progressive muscle weakness. DMD is caused by mutations in the dystrophin (dmd) gene resulting in very low levels or a complete absence of the dystrophin protein, a key structural element of muscle fibres which is responsible for the proper transmission of force. In the absence of dystrophin, muscle fibres become damaged easily during contraction resulting in their degeneration. DMD patients and mdx mice (an animal model of DMD) exhibit altered metabolic disturbances that cannot be attributed to the loss of dystrophin directly. We tested the hypothesis that glycogen metabolism is defective in mdx dystrophic mice.

Results

Dystrophic mdx mice had increased skeletal muscle glycogen (79%, (P<0.01)). Skeletal muscle glycogen synthesis is initiated by glycogenin, the expression of which was increased by 50% in mdx mice (P<0.0001). Glycogen synthase activity was 12% higher (P<0.05) but glycogen branching enzyme activity was 70% lower (P<0.01) in mdx compared with wild-type mice. The rate-limiting enzyme for glycogen breakdown, glycogen phosphorylase, had 62% lower activity (P<0.01) in mdx mice resulting from a 24% reduction in PKA activity (P<0.01). In mdx mice glycogen debranching enzyme expression was 50% higher (P<0.001) together with starch-binding domain protein 1 (219% higher; P<0.01). In addition, mdx mice were glucose intolerant (P<0.01) and had 30% less liver glycogen (P<0.05) compared with control mice. Subsequent analysis of the enzymes dysregulated in skeletal muscle glycogen metabolism in mdx mice identified reduced glycogenin protein expression (46% less; P<0.05) as a possible cause of this phenotype.

Conclusion

We identified that mdx mice were glucose intolerant, and had increased skeletal muscle glycogen but reduced amounts of liver glycogen.

[A genetic systemic disease: clinical description of type 1 myotonic dystrophy in adults]

Type 1 myotonic dystrophy is an autosomal dominant inherited disorder related to the expansion of a trinucleotide (CTG) repeat in the exon 15 in the 3'-untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. Mutant transcripts containing an expanded CUG repeat are retained in nuclear foci and cause numerous dysfunctions by interfering with biogenesis of other mRNAs. Prominent clinical features are progressive muscular weakness and myotonia, which affect skeletal muscles but also white muscles leading to digestive, urinary and obstetrical disorders. Functional prognosis correlates with motor handicap and vital prognosis is linked to cardiac rhythm disturbances and conduction defects due to progressive subendocardial fibrosis, and to complex respiratory dysfunctions, which associate restrictive lung disease, involvement of the central inspiratory pathway, and sleep apnea. Other clinical features are lens opacity, glucose intolerance, metabolic syndrome, several endocrine disorders (gonadal deficiency, hyperparathydoidism), or immunoglobulin deficiency due to immunoglobulin G hypercatabolism. Life expectancy is reduced in myotonic dystrophy, and death is mainly caused by respiratory complications, but also by cardiac arrhythmias. Moreover, an abnormal incidence of tumors has been reported. Therefore, myotonic dystrophy does not only concern neurologists but a multidisciplinary approach is necessary, including at least pneumologist, cardiologist, and physiotherapist. General internists should also be implicated, not only in the initial diagnosis step, but also in the diagnosis of complications and their treatments.

Muscular dystrophies at different ages: metabolic and endocrine alterations

Common metabolic and endocrine alterations exist across a wide range of muscular dystrophies. Skeletal muscle plays an important role in glucose metabolism and is a major participant in different signaling pathways. Therefore, its damage may lead to different metabolic disruptions. Two of the most important metabolic alterations in muscular dystrophies may be insulin resistance and obesity. However, only insulin resistance has been demonstrated in myotonic dystrophy. In addition, endocrine disturbances such as hypogonadism, low levels of testosterone, and growth hormone have been reported. This eventually will result in consequences such as growth failure and delayed puberty in the case of childhood dystrophies. Other consequences may be reduced male fertility, reduced spermatogenesis, and oligospermia, both in childhood as well as in adult muscular dystrophies. These facts all suggest that there is a need for better comprehension of metabolic and endocrine implications for muscular dystrophies with the purpose of developing improved clinical treatments and/or improvements in the quality of life of patients with dystrophy. Therefore, the aim of this paper is to describe the current knowledge about of metabolic and endocrine alterations in diverse types of dystrophinopathies, which will be divided into two groups: childhood and adult dystrophies which have different age of onset.

Decreased concentration of adiponectin together with a selective reduction of its high molecular weight oligomers is involved in metabolic complications of myotonic dystrophy type 1

OBJECTIVE

The hormone adiponectin exerts beneficial pleiotropic effects on biological and metabolic processes. Although a well-recognized insulin sensitizer, its characteristic has yet to be clearly defined. Myotonic dystrophy type 1 (DM1) is a rare genetic disorder that features muscle wasting and metabolic comorbidity, and patients have an increased risk of developing type 2 diabetes. We analyzed circulating levels of adiponectin and its oligomers to determine whether their expression correlates with metabolic alterations in DM1 patients.

DESIGN AND METHODS

We measured the anthropometric and biochemical features and three insulin resistance (IR) indices (homeostasis model assessment, quantitative insulin sensitivity check index, and McAuley) of 21 DM1 patients and of 82 age-, sex-, and weight-matched controls. In the blood samples of patients and controls, adiponectin levels were measured by ELISA, and its oligomers were characterized by using western blotting and gel filtration. The adiponectin gene was molecularly analyzed in patients.

RESULTS

DM1 patients had significantly higher body mass index, waist circumference, triglycerides (TGs), glucose, tumor necrosis factor α, and IR; conversely, they had significantly lower concentrations of total serum adiponectin with a selective, pronounced decrease of its high molecular weight (HMW) oligomers. There was a strong negative correlation between adiponectin and TGs in DM1 patients.

CONCLUSIONS

Our results endorse the hypothesis that decreased expression of adiponectin together with a selective reduction of its HMW oligomers contributes to the worsening of IR and its metabolic complications in DM1 patients. These findings suggest that adiponectin and HMW oligomers may serve as biomarkers and are promising therapeutic agents for IR and its consequences in DM1.

[A survey of cardiologists, diabetologists, gynecologists and ophthalmologists practicing in Osaka on the medical consultation behaviors of myotonic dystrophy patients]

An anonymous postal survey of cardiologists, diabetologists, gynecologists, and ophthalmologists in Osaka was performed to assess the medical care-seeking behaviors of and problems associated with the medical management of patients with myotonic dystrophy (DM). The questionnaires were sent to 927 cardiologists, 357 diabetologists, 882 gynecologists, and 915 ophthalmologists. Of these, 172 cardiologists, 85 diabetologists, 220 gynecologists, and 154 ophthalmologists responded. More than 30% of responders had provided care to DM patients, and approximately 10% had experience diagnosing DM patients. These facts suggest that DM patients receive medical care from various specialists due to complications involving multiple systems and some of them visit other specialists prior to neurologists. Some patients were diagnosed after perinatal or perioperative difficulties. Therefore, it seems important to improve the ability of physicians to identify DM patients. Because specialists with experience diagnosing DM paid more attention to the characteristic features of DM, such as grip myotonia and hatchet face, a simple screening test may be useful for detecting DM. Some responders pointed out the negative attitude of DM patients toward medical care and the lack of neurologists for consultation as problems in the medical management of DM patients. Cooperation among neurologists and other specialists and education of DM patients are important to improve the medical management of DM patients.

Organ dysfunction and muscular disability in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder characterized by muscle weakness and multiple organ impairment, especially the eyes, lung, and heart. We conducted the current study to analyze the prevalence and intercorrelation among these disorders and their respective relationships with muscular disability. We assessed medical history, anthropometric data, lung volumes, arterial and venous blood samples, surface 12-lead electrocardiogram, echocardiography, ophthalmologic examination, and muscular impairment rating scale (MIRS) in 106 patients (48 male and 58 female) with DM1, aged 43.7 ± 12.8 years. Obesity, hypertriglyceridemia, and diabetes were found in respectively 25.6%, 47.6%, and 17.1% of patients. Disabling cataract was found in 43.4%, and was independently predicted by age and MIRS. Restrictive lung disease was noted in 34%, and was predicted by MIRS, CTG repeat expansion, and body mass index. Conduction disorders were found in 30.2% of patients and were predicted by left ventricular ejection fraction, MIRS, and CTG repeat expansion.We found significant relationships between cataract, restrictive lung disease, and conduction disorders: patients with cataract and those with conduction disorders exhibited more severe restrictive lung disease than the other patients. Conversely, the relative risk of restrictive lung disease was 2.42 (1% confidence interval [CI], 1.06-5.51) in patients with cataract and 2.54 (1% CI, 1.26-5.07) in patients with conduction disorders. Multivariate analysis revealed that MIRS was the only independent predictor for conduction disorders and restrictive lung disease. MIRS ≥3 and MIRS ≥4 were the best simple cutoff values to predict, respectively, lung and cardiac involvements.To conclude, muscular disability, ophthalmologic, and cardiac and pulmonary involvement are strongly correlated. Particular attention should be given to these entities in patients with distal or proximal muscular weakness.

[Successful treatment of recurrent hypoglycemia by pioglitazone in a patient with myotonic dystrophy]

A 20 year-old woman with myotonic dystrophy type 1 (DM1) presented with fatigue, daytime somnolence, and sudden poor responsiveness. Blood glucose was measured before and after each meal for 4 days, and hypoglycemia was confirmed twice, although neither perspiration nor palpitations occurred in the hypoglycemic state. On a 75 g oral glucose tolerance test (OGTT), fasting blood glucose level was 83 mg/dl, and fasting blood immunoreactive insulin (IRI) level was 5.96 microIU/ml. However, IRI increased to 528 microIU/ml at 60 minutes and blood glucose decreased to 57 mg/dl at 120 minutes of the OGTT. The patient was diagnosed with reactive hypoglycemia due to excessive insulin secretion. Oral administration of pioglitazone improved the excessive insulin secretion as assessed by OGTT. After starting treatment, hypoglycemia was not detected either pre- or post-prandially. After 10 months of treatment, blood glucose level after glucose loading was higher than fasting blood glucose level during OGTT, and the IRI area under the curve of the OGTT decreased. We considered that hypoglycemia unawareness resulted from recurrent hypoglycemic episodes in this patient. Pioglitazone was effective in improving hyperinsulinemia and reactive hypoglycemia in nondiabetic DM1.

Dramatic improvement of blood glucose control after pioglitazone treatment in poorly controlled over-weight diabetic patients with myotonic dystrophy

Insulin resistance is mainly present in skeletal muscle in non-obese patients with myotonic dystrophy. Thiazolidinediones are reported to reduce insulin resistance in these patients. However, the effects of pioglitazone in overweight patients with myotonic dystrophy and type 2 diabetes mellitus have not been established. Here, we evaluated the effect of pioglitazone in two poorly-controlled over-weight diabetic patients with myotonic dystrophy. Case 1 was a 41- year-old women (BMI 27.8 kg/m(2)) with myotonic dystrophy and type 2 diabetes had been treated with 3 mg/day glimepiride and 500 mg/day metformin, but the treatment failed to achieve good glycemic control (HbA(1C) 11.8 %). Following admission to the hospital, she was treated with low-dose insulin and 30 mg/day pioglitazone. At 10 days after initiation of therapy, glycemic control was improved, serum IL-6 and hs-CRP decreased, and adiponectin level increased rapidly. Case 2 was a 47-year-old women (BMI 29.2 kg/m(2)) with myotonic dystrophy and type 2 diabetes mellitus had been treated with insulin without successful glycemic control (HbA(1C) 10.3 %). After admission, she was treated with 15 mg/day pioglitazone. This improved glycemic control, reduced daily insulin requirement, decreased IL-6 and hs-CRP levels rapidly and increased adiponectin level at 10 days after initiation of therapy. In both cases, pioglitazone rapidly improved glycemic control, enhanced adiponectin production, and reduced inflammatory cytokines. These results suggest that pioglitazone may be suitable for these patients.