Randomized controlled trial of testosterone in myotonic dystrophy

Endocrine Dysfunction in Patients With Myotonic Dystrophy

Myotonic dystrophy is a dominantly inherited multisystem disorder that results from increased CTG repeats in the 3' region of the myotonic dystrophy protein kinase gene (DMPK). The mutant DMPK mRNA remains in the nucleus and sequesters RNA-binding proteins, including regulators of mRNA splicing. Myotonic dystrophy is characterized by a highly variable phenotype that includes muscle weakness and myotonia, and the disorder may affect the function of many endocrine glands. DMPK mRNA is expressed in muscle, testis, liver, pituitary, thyroid, and bone; the mutated form leads to disruption of meiosis and an increase in fetal insulin receptor-A relative to adult insulin receptor-B, resulting in adult primary testicular failure and insulin resistance predisposing to diabetes, respectively. Patients with myotonic dystrophy are also at increased risk for hyperlipidemia, nonalcoholic fatty liver disease, erectile dysfunction, benign and malignant thyroid nodules, bone fractures, miscarriage, preterm delivery, and failed labor during delivery. Circulating parathyroid hormone and adrenocorticotropic hormone levels may be elevated, but the mechanisms for these associations are unclear. This review summarizes what is known about endocrine dysfunction in individuals with myotonic dystrophy.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Myotonic dystrophy patient preferences in patient-reported outcome measures

INTRODUCTION

When preparing for clinical trials in myotonic dystrophy type-1 (DM1), it is important that researchers develop and identify patient-reported outcome measures with good measurement properties.

METHODS

Fifty-two DM1 patients enrolled in 2 clinical studies completed the Myotonic Dystrophy Health Index (MDHI), 36-Item Short Form Health Survey (version 2; SF-36v2), Individualized Neuromuscular Quality of Life questionnaire (INQoL), and a questionnaire comparing the relevance, usability, overall preference, and perceived responsiveness of each measure. The associations between instrument scores and physical function, genetic test results, and employment status were examined.

RESULTS

The MDHI was preferred over the INQoL in 13 of 13 areas and was preferred over the SF-36v2 in 9 of 13 areas. The MDHI was the only score that was associated with participant employment status, CTG repeat length, and the 3 measurements of clinical function.

DISCUSSION

The MDHI correlates well with physical function and is viewed favorably by participants in DM1 clinical studies. Muscle Nerve, 2018.

Treatment of Men for “Low Testosterone”: A Systematic Review

Testosterone products are recommended by some prescribers in response to a diagnosis or presumption of “low testosterone” (low-T) for cardiovascular health, sexual function, muscle weakness or wasting, mood and behavior, and cognition. We performed a systematic review of 156 eligible randomized controlled trials in which testosterone was compared to placebo for one or more of these conditions. We included studies in bibliographic databases between January 1, 1950 and April 9, 2016, and excluded studies involving bodybuilding, contraceptive effectiveness, or treatment of any condition in women or children. Studies with multiple relevant endpoints were included in all relevant tables. Testosterone supplementation did not show consistent benefit for cardiovascular risk, sexual function, mood and behavior, or cognition. Studies that examined clinical cardiovascular endpoints have not favored testosterone therapy over placebo. Testosterone is ineffective in treating erectile dysfunction and controlled trials did not show a consistent effect on libido. Testosterone supplementation consistently increased muscle strength but did not have beneficial effects on physical function. Most studies on mood-related endpoints found no beneficial effect of testosterone treatment on personality, psychological well-being, or mood. The prescription of testosterone supplementation for low-T for cardiovascular health, sexual function, physical function, mood, or cognitive function is without support from randomized clinical trials.

Myotonic dystrophy health index: Correlations with clinical tests and patient function

INTRODUCTION

The Myotonic Dystrophy Health Index (MDHI) is a disease-specific patient-reported outcome measure. Here, we examine the associations between the MDHI and other measures of disease burden in a cohort of individuals with myotonic dystrophy type-1 (DM1).

METHODS

We conducted a cross-sectional study of 70 patients with DM1. We examined the associations between MDHI total and subscale scores and scores from other clinical tests. Participants completed assessments of strength, myotonia, motor and respiratory function, ambulation, and body composition. Participants also provided blood samples, underwent physician evaluations, and completed other patient-reported outcome measures.

RESULTS

MDHI total and subscale scores were strongly associated with muscle strength, myotonia, motor function, and other clinical measures.

CONCLUSIONS

Patient-reported health status, as measured by the MDHI, is associated with alternative measures of clinical health. These results support the use of the MDHI as a valid tool to measure disease burden in DM1 patients.

Congenital and childhood myotonic dystrophy: Current aspects of disease and future directions

Myotonic dystrophy type 1 (DM1) is multisystem disease arising from mutant CTG expansion in the non-translating region of the dystrophia myotonica protein kinase gene. While DM1 is the most common adult muscular dystrophy, with a worldwide prevalence of one in eight thousand, age of onset varies from before birth to adulthood. There is a broad spectrum of clinical severity, ranging from mild to severe, which correlates with number of DNA repeats. Importantly, the early clinical manifestations and management in congenital and childhood DM1 differ from classic adult DM1. In neonates and children, DM1 predominantly affects muscle strength, cognition, respiratory, central nervous and gastrointestinal systems. Sleep disorders are often under recognised yet a significant morbidity. No effective disease modifying treatment is currently available and neonates and children with DM1 may experience severe physical and intellectual disability, which may be life limiting in the most severe forms. Management is currently supportive, incorporating regular surveillance and treatment of manifestations. Novel therapies, which target the gene and the pathogenic mechanism of abnormal splicing are emerging. Genetic counselling is critical in this autosomal dominant genetic disease with variable penetrance and potential maternal anticipation, as is assisting with family planning and undertaking cascade testing to instigate health surveillance in affected family members. This review incorporates discussion of the clinical manifestations and management of congenital and childhood DM1, with a particular focus on hypersomnolence and sleep disorders. In addition, the molecular genetics, mechanisms of disease pathogenesis and development of novel treatment strategies in DM1 will be summarised.

Gonadal failure is associated with visceral adiposity in myotonic dystrophies

BACKGROUND

Hypogonadism occurs in myotonic dystrophies type 1 (MD1) and type 2 (MD2). Sertoli and Leydig cell secretions, including insulin-like peptide-3 (INSL3), anti-Müllerian hormone (AMH) and inhibin B, were evaluated in male patients with MD.

DESIGN

Academic settings. Forty-four male patients with MD [31 MD1, 13 MD2, aged 59 (50-64) years, median (interquartile range)], age-, sex- and BMI-matched non-MD hypogonadal patients (n = 14) and healthy controls (n = 32). Serum FSH, LH, inhibin B, AMH, testosterone (T) and INSL3 were measured; fat and muscle masses were evaluated by DEXA.

RESULTS

Overt primary hypogonadism occurred in 29% of patients with MD1 and 46% of patients with MD2. Considering subclinical forms, the prevalence increased to 69% of MD1 and 100% of MD2. A half of patients with MD experienced symptoms. INSL3 levels were unaffected in most patients with MD. By contrast, AMH and inhibin B were reduced in most patients with MD and unrelated to age. Patients with MD showed increased body and visceral fat. Free T levels were negatively predicted by fat mass, and AMH and FSH levels were negatively correlated with waist/hip ratio and fat mass. AMH, inhibin B and FSH levels positively correlated with muscle strength and muscle mass.

CONCLUSIONS

AMH and inhibin B secretion failures are common in male patients with MD and are more severe than Leydig cell hormones impairment. AMH and inhibin B measurements might provide clinical utility in evaluating fertility in patients with MD. Serum T, AMH and inhibin B productions are negatively influenced by increased fat mass, while AMH and inhibin B might be markers of muscle impairment.

Myotonic dystrophy

Myotonic dystrophy (dystrophia myotonica, DM) is one of the most common lethal monogenic disorders in populations of European descent. DM type 1 was first described over a century ago. More recently, a second form of the disease, DM type 2 was recognized, which results from repeat expansion in a different gene. Both disorders have autosomal dominant inheritance and multisystem features, including myotonic myopathy, cataract, and cardiac conduction disease. This article reviews the clinical presentation and pathophysiology of DM and discusses current management and future potential for developing targeted therapies.

Hypogonadism in DM1 and its relationship to erectile dysfunction

Myotonic dystrophy type 1 (DM1) is characterized by both a premature appearance of age-related phenotypes and multiple organ involvement, which affects skeletal and smooth muscle as well as the eye, heart, central nervous system, and endocrine system. Although erectile dysfunction (ED) is a frequent complaint in patients with DM1, it has not been investigated in great depth. Hypogonadism, which is reported to be one of the physical causes of ED in the general population, frequently occurs in DM1. We planned this case-control study to evaluate the relationship between hypogonadism, as defined by the sexual hormone profile (FSH, LH, testosterone (T) and prolactin) and ED, as assessed by means of an internationally validated self-administered questionnaire (IIEF). DM1 patients had significantly increased mean levels of both gonadotropins (FSH and LH) (p < 0.0001) and a reduced mean level of T (p < 0.0001) when compared to controls. Twelve patients were eugonadic (normal LH, T, and FSH), while 18 displayed hormonal evidence of hypogonadism, characterized by tubular failure (increased FSH) in all the subjects and associated with interstitial failure in 14 subjects: seven with primary hypogonadism (increased LH and reduced T) and seven with compensated hypogonadism (increased LH and normal T). Patients with hormonal evidence of interstitial failure had a larger CTG expansion (p = 0.008), longer disease duration (p = 0.013), higher grade of disease (p = 0.004) and lower erectile function score (p = 0.02) than eugonadic patients. Impotence occurred in 13/14 hypogonadic patients with interstitial failure and in 5/12 eugonadic patients (p = 0.017, OR = 18.2).

Myotonic dystrophy types 1 and 2

Myotonic dystrophies (dystrophia myotonica, or DM) are inherited disorders characterized by myotonia and progressive muscle degeneration, which are variably associated with a multisystemic phenotype. To date, two types of myotonic dystrophy, type 1 (DM1) and type 2 (DM2), are known to exist; both are autosomal dominant disorders caused by expansion of an untranslated short tandem repeat DNA sequence (CTG)(n) and (CCTG)(n), respectively. These expanded repeats in DM1 and DM2 show different patterns of repeat-size instability. Phenotypes of DM1 and DM2 are similar but there are some important differences, most conspicuously in the severity of the disease (including the presence or absence of the congenital form), muscles primarily affected (distal versus proximal), involved muscle fiber types (type 1 versus type 2 fibers), and some associated multisystemic phenotypes. The pathogenic mechanism of DM1 and DM2 is thought to be mediated by the mutant RNA transcripts containing expanded CUG and CCUG repeats. Strong evidence supports the hypothesis that sequestration of muscle-blind like (MBNL) proteins by these expanded repeats leads to misregulated splicing of many gene transcripts in corroboration with the raised level of CUG-binding protein 1. However, additional mechanisms, such as changes in the chromatin structure involving CTCN-binding site and gene expression dysregulations, are emerging. Although treatment of DM1 and DM2 is currently limited to supportive therapies, new therapeutic approaches based on pathogenic mechanisms may become feasible in the near future.

Open-label trial of recombinant human insulin-like growth factor 1/recombinant human insulin-like growth factor binding protein 3 in myotonic dystrophy type 1

OBJECTIVE

To evaluate the safety and tolerability of recombinant human insulin-like growth factor 1 (rhIGF-1) complexed with IGF binding protein 3 (rhIGF-1/rhIGFBP-3) in patients with myotonic dystrophy type 1 (DM1).

DESIGN

Open-label dose-escalation clinical trial.

SETTING

University medical center.

PARTICIPANTS

Fifteen moderately affected ambulatory participants with genetically proven myotonic dystrophy type 1.

INTERVENTION

Participants received escalating dosages of subcutaneous rhIGF-1/rhIGFBP-3 for 24 weeks followed by a 16-week washout period.

MAIN OUTCOME MEASURES

Serial assessments of safety, muscle mass, muscle function, and metabolic state were performed. The primary outcome variable was the ability of participants to complete 24 weeks receiving rhIGF-1/ rhIGFBP-3 treatment.

RESULTS

All participants tolerated rhIGF-1/rhIGFBP-3. There were no significant changes in muscle strength or functional outcomes measures. Lean body muscle mass measured by dual-energy x-ray absorptiometry increased by 1.95 kg (P < .001) after treatment. Participants also experienced a mean reduction in triglyceride levels of 47 mg/dL (P = .002), a mean increase in HDL levels of 5.0 mg/dL (P = .03), a mean reduction in hemoglobin A(1c) levels of 0.15% (P = .03), and a mean increase in testosterone level (in men) of 203 ng/dL (P = .002) while taking rhIGF-1/rhIGFBP-3. Mild reactions at the injection site occurred (9 participants), as did mild transient hypoglycemia (3), lightheadedness (2), and transient papilledema (1).

CONCLUSIONS

Treatment with rhIGF-1/rhIGFBP-3 was generally well tolerated in patients with myotonic dystrophy type 1. Treatment with rhIGF-1/rhIGFBP-3 was associated with increased lean body mass and improvement in metabolism but not increased muscle strength or function. Larger randomized controlled trials would be needed to further evaluate the efficacy and safety of this medication in patients with neuromuscular disease.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00233519.

ISSN exercise & sport nutrition review: research & recommendations

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper is a five year update of the sports nutrition review article published as the lead paper to launch the JISSN in 2004 and presents a well-referenced overview of the current state of the science related to how to optimize training and athletic performance through nutrition. More specifically, this paper provides an overview of: 1.) The definitional category of ergogenic aids and dietary supplements; 2.) How dietary supplements are legally regulated; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of the ergogenic value of nutrition and dietary supplementation in regards to weight gain, weight loss, and performance enhancement. Our hope is that ISSN members and individuals interested in sports nutrition find this review useful in their daily practice and consultation with their clients.

Anabolic agents for improving muscle regeneration and function after injury

1. In the present review, we describe how muscles can be injured by external factors, internal factors or during the performance of some actions during sports. In addition, we describe the injury to a muscle that occurs when its blood supply is interrupted, an occurrence common in clinical settings. An overview of muscle regeneration is presented, as well as a discussion of some of the potential complications that can compromise successful muscle repair and lead to impaired function and permanent disability. 2. Improving muscle regeneration is important for hastening muscle repair and restoring muscle function and the present review describes ways in which this can be achieved. We describe recent advances in tissue engineering that offer considerable promise for treating muscle damage, but highlight the fact that these techniques require rigorous evaluation before they can become mainstream clinical treatments. 3. Growth-promoting agents are purported to increase the size of existing and newly regenerating muscle fibres and, therefore, could be used to improve muscle function if administered at appropriate times during the repair process. The present review provides an update on the efficacy of some growth-promoting agents, including anabolic steroids, insulin-like growth factor-I (IGF-I) and beta(2)-adrenoceptor agonists, to improve muscle function after injury. Although these approaches have clinical merit, a better understanding of the androgenic, IGF-I and b-adrenoceptor signalling pathways in skeletal muscle is important if we are to devise safe and effective therapies to enhance muscle regeneration and function after injury.

Myotonic dystrophy: therapeutic strategies for the future

Myotonic dystrophy (DM) is a dominantly inherited neurodegenerative disorder for which there is no cure or effective treatment. Investigation of DM pathogenesis has identified a novel disease mechanism that requires development of innovative therapeutic strategies. It is now clear that DM is not caused by expression of a mutant protein. Instead, DM is the first recognized example of an RNA-mediated disease. Expression of the mutated gene gives rise to an expanded repeat RNA that is directly toxic to cells. The mutant RNA is retained in the nucleus, forming ribonuclear inclusions in affected tissue. A primary consequence of RNA toxicity in DM is dysfunction of two classes of RNA binding proteins, which leads to abnormal regulation of alternative splicing, or spliceopathy, of select genes. Spliceopathy now is known to cause myotonia and insulin resistance in DM. As our understanding of pathogenesis continues to improve, therapy targeted directly at the RNA disease mechanism will begin to replace the supportive care currently available. New pharmacologic approaches to treat myotonia and muscle wasting in DM type 1 are already in early clinical trials, and therapies designed to reverse the RNA toxicity have shown promise in preclinical models by correcting spliceopathy and eliminating myotonia. The well-defined ribonuclear inclusions may serve as convenient therapeutic targets to identify new agents that modify RNA toxicity. Continued development of appropriate model systems will allow testing of additional therapeutic strategies as they become available. Although DM is a decidedly complex disorder, its RNA-mediated disease mechanism may prove to be highly susceptible to therapy.

Hypogonadism is common in men with myopathies

BACKGROUND

Hypogonadism has been described in patients with myotonic muscular dystrophy type 1 but has not been evaluated in other myopathies.

METHODS

We measured total and free serum testosterone levels in 59 men with myotonic muscular dystrophy type 1 (N = 12), facioscapulohumeral muscular dystrophy (N = 11), dystrophinopathy (N = 12), metabolic myopathy (N = 7), and inclusion body myositis (N = 17) and compared these with the normal reference interval.

RESULTS

Thirty-two of the 59 (54%) participants had low total testosterone, 23 (39%) had low total and free values, and 5 (8%) had low free with normal total levels. There were no significant differences in the prevalence of hypogonadism between those with myotonic muscular dystrophy type 1 and the other groups even after considering age as a confounder.

CONCLUSIONS

Hypogonadism is common in men with myopathies, and with the importance of testosterone in the maintenance of muscle mass, treatment of hypogonadism should be considered.

Computerized hand grip myometry reliably measures myotonia and muscle strength in myotonic dystrophy (DM1)

The aim of this study was to develop a reliable, sensitive, quantitative measure of grip myotonia and strength and to determine whether CTG repeat length is correlated with grip myotonia and with muscle strength in myotonic dystrophy type 1 (DM1). Three maximum voluntary isometric contractions (MVICs) of the finger flexors (i.e., handgrip) were recorded on 2 successive days using a computerized handgrip myometer in 29 genetically confirmed DM1 patients and 17 normals. An automated computer program calculated MVIC peak force (PF) and relaxation times (RTs) along the declining (relaxation) phase of the force recordings at 90%, 75%, 50%, 10%, and 5% of PF. Patients also underwent quantitative strength testing (QST) manual muscle testing (MMT). The patients had longer grip RTs and lower PFs than normals. RT (90% to 5%) was above the normal mean +2.5 SD in 25 (86%) patients. In DM1, prolongation of RT was mainly in the terminal (50% to 5%), rather than the initial (90% to 50%) phase of relaxation. PFs and RTs for each patient were reproducible on consecutive days. RTs were positively correlated with leukocyte CTG repeat length, whereas measures of muscle strength, such as PF, QST, and MMT, were negatively correlated with repeat length. We conclude that computerized handgrip myometry provides a sensitive, reliable measure of myotonia and strength in DM1 and offers a method to assess natural history and response to treatment.

Therapeutic approaches for muscle wasting disorders

Muscle wasting and weakness are common in many disease states and conditions including aging, cancer cachexia, sepsis, denervation, disuse, inactivity, burns, HIV-acquired immunodeficiency syndrome (AIDS), chronic kidney or heart failure, unloading/microgravity, and muscular dystrophies. Although the maintenance of muscle mass is generally regarded as a simple balance between protein synthesis and protein degradation, these mechanisms are not strictly independent, but in fact they are coordinated by a number of different and sometimes complementary signaling pathways. Clearer details are now emerging about these different molecular pathways and the extent to which these pathways contribute to the etiology of various muscle wasting disorders. Therapeutic strategies for attenuating muscle wasting and improving muscle function vary in efficacy. Exercise and nutritional interventions have merit for slowing the rate of muscle atrophy in some muscle wasting conditions, but in most cases they cannot halt or reverse the wasting process. Hormonal and/or other drug strategies that can target key steps in the molecular pathways that regulate protein synthesis and protein degradation are needed. This review describes the signaling pathways that maintain muscle mass and provides an overview of some of the major conditions where muscle wasting and weakness are indicated. The review provides details on some therapeutic strategies that could potentially attenuate muscle atrophy, promote muscle growth, and ultimately improve muscle function. The emphasis is on therapies that can increase muscle mass and improve functional outcomes that will ultimately lead to improvement in the quality of life for affected patients.

Drug treatment for myotonia

BACKGROUND

Abnormal delayed relaxation of skeletal muscles, known as myotonia, can cause disability in myotonic disorders. Sodium channel blockers, tricyclic antidepressive drugs, benzodiazepines, calcium-antagonists, taurine and prednisone may be of use in reducing myotonia.

OBJECTIVES

To consider the evidence from randomised controlled trials on the efficacy and tolerability of drug treatment in patients with clinical myotonia due to a myotonic disorder.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (April 2004), MEDLINE (January 1966 to December 2003) and EMBASE (January 1980 to December 2003). Grey literature was handsearched and reference lists of identified studies and reviews were examined. Authors, disease experts and manufacturers of anti-myotonic drugs were contacted.

SELECTION CRITERIA

We considered all (quasi) randomised trials of participants with myotonia treated with any drug treatment versus no therapy, placebo or any other active drug treatment. The primary outcome measure was:reduced clinical myotonia using two categories: (1) no residual myotonia or improvement of myotonia or (2) No change or worsening of myotonia. Secondary outcome measures were:(1) clinical relaxation time; (2) electromyographic relaxation time; (3) stair test; (4) presence of percussion myotonia; and (5) proportion of adverse events.

DATA COLLECTION AND ANALYSIS

Two authors extracted the data independently onto standardised extraction forms and disagreements were resolved by discussion.

MAIN RESULTS

Nine randomised controlled trials were found comparing active drug treatment versus placebo or another active drug treatment in patients with myotonia due to a myotonic disorder. Included trials were double-blind or single-blind crossover studies involving a total of 137 patients of which 109 had myotonic dystrophy type 1 and 28 had myotonia congenita. The studies were of poor quality. Therefore, we were not able to analyse the results of all identified studies. Two small crossover studies without a washout period demonstrated a significant effect of imipramine and taurine in myotonic dystrophy. One small crossover study with a washout period demonstrated a significant effect of clomipramine in myotonic dystrophy. Meta-analysis was not possible.

AUTHORS' CONCLUSIONS

Due to insufficient good quality data and lack of randomised studies, it is impossible to determine whether drug treatment is safe and effective in the treatment of myotonia. Small single studies give an indication that clomipramine and imipramine have a short-term beneficial effect and that taurine has a long-term beneficial effect on myotonia. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.

ISSN Exercise & Sport Nutrition Review: Research & Recommendations

Sport nutrition is a constantly evolving field with literally thousands of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper presents a well-referenced overview of the current state of the science related to how to optimize training through nutrition. More specifically, this article discusses: 1.) how to evaluate the scientific merit of nutritional supplements; 2.) general nutritional strategies to optimize performance and enhance recovery; and, 3.) our current understanding of the available science behind weight gain, weight loss, and performance enhancement supplements. Our hope is that ISSN members find this review useful in their daily practice and consultation with their clients.

Treatment in myotonia and periodic paralysis

The myotonic disorders, including the myotonic dystrophies (myotonic dystrophy type 1, DM1; myotonic dystrophy type 2, DM2/PROMM/PDM), the muscle channelopathies or non-dystrophic myotonias (chloride, sodium, calcium and potassium channelopathies) are all characterized by myotonia and muscle weakness despite different pathophysiology involved in these disorders. Myotonia may affect the eye, facial and jaw muscles as well as the hands and legs. It may be painful and disabling. Muscle weakness may be episodical as in the paralytic attacks of the sodium and calcium channelopathies or culminate in permanent muscle weakness as in the calcium channelopathies and some sodium channelopathies associated to specific point mutations. The severity of myotonia may fluctuate in the myotonic dystrophies, but weakness is usually fixed, affecting neck flexors, facial and jaw muscles as well as proximal and distal muscles of the limbs. Despite the recent progress in molecular genetics the precise mechanisms responsible for myotonia and weakness are not fully understood and there is no standardized treatment strategy. We present a review of selected treatment trials in the myotonic disorders and the muscle channelopathies, and discuss our experience in the treatment of myotonia and muscle weakness, with reference to the limits and advantages of treatment trials in this field.

Regulation of body composition by androgens

Human body can be viewed simplistically as being composed of fat-free and fat mass. With more sophisticated techniques, body composition can be broken down into fat mass, skeletal muscle mass, nonmuscle lean mass, visceral mass and bone mineral content. Similarly, it is possible to obtain estimates of total body water and intracellular and extracellular water contents. Regardless of the model of body composition assessment, it is evident that androgens are important determinants of body composition; there is no body compartment that is not directly or indirectly affected by androgens. The effects of androgens on skeletal muscle mass have received the greatest attention in recent literature; however, growing body of evidence suggests that androgens also regulate fat mass, bone mineral content, nonmuscle soft tissues and body water.

Sexuality and disease

Disease is commonly associated with sexual dysfunction in both men and women. In many cases, effective treatments are available that can improve libido, erectile dysfunction, and vaginal dryness. Sexual problems in older persons with disease often lead to anxiety, marital discord, and withdrawal. It is the responsibility of all health care professionals to inquire about sexuality in all patients, no matter what the patient's age, and to be aware that frailty [79-81] is not, in itself, a barrier to sexuality. Health professionals need to give education, support, and counseling on sexuality for patients with disease.

Androgen effects on body composition

Androgens are known to have a role in the body fat, muscle size, muscle performance and physical function differences seen between hypogonadal and eugonadal men. The results of investigations into effects of testosterone on body composition, fat metabolism and muscle anabolism are reviewed here. Testosterone dose-response relationships are presented in studies of the effects of physiologic and supraphysiologic doses with and without exercise in young hypogonadal men, older men with low testosterone levels and in chronic illness states.

Quantitative motor assessment in myotonic dystrophy

OBJECTIVE

To establish baseline data, using a quantitative motor evaluation protocol, prior to a prospective longitudinal study of the natural history of muscular involvement in myotonic dystrophy (DM).

DESIGN/METHODS

We conducted a cross-sectional study using a protocol consisting of manual muscle testing (MMT), quantitative muscle testing (QMT), and timed functional testing (TFT) on 50 definite DM patients (27 men, 23 women), aged 16 to 67 years. The relationships between MMT, QMT and TFT scores and disease duration were examined using linear regression analysis.

RESULTS

The muscle weakness was symmetric and the neck flexors and the distal muscles of upper and lower extremities were weaker than proximal muscles. Using MMT scores, the average strength decline was 0.95% per year and was similar for men and women. The strength decline was significantly more rapid for distal muscles than for proximal muscles. Quantitative muscle testing scores documented a strength decline per year of disease duration of 1.2-1.6% for the hip flexors and of 2.0-3.0% for the hand grip flexors.

CONCLUSIONS

We observed significant linear relationships between the scores generated by this protocol and disease duration. These data illustrate the distal to proximal progression of muscular involvement in DM, a pattern of progression well-recognized by the clinicians. The follow-up assessment of a large DM cohort in a longitudinal study will establish whether this quantitative protocol provides sensitive measures of the disease progression.

Hypogonadism and androgen replacement therapy in elderly men

The decrease in testosterone levels with age is both central (pituitary) and peripheral (testicular) origin. Because serum levels of sex-hormone-binding globulin increase with aging, the decrease in free testosterone is of even greater magnitude. Recent long-term studies of testosterone therapy in hypogonadal elderly men have shown beneficial effects on bone density, body composition, and muscle strength without any substantial adverse effects on lipids and the prostate. Total testosterone level is the test of choice for initial screening of elderly men who present with signs and symptoms of hypogonadism. If the level is below 300 ng/dL, replacement therapy should be initiated. If the level is normal in a symptomatic patient, free or bioavailable testosterone should be determined. The pros and cons of testosterone therapy should be discussed in depth with every patient, and decisions should be made on an individual basis. This review summarizes the trials of testosterone replacement therapy in elderly men and outlines a diagnostic approach to these patients.

Can androgen therapy replete lean body mass and improve muscle function in wasting associated with human immunodeficiency virus infection?

A significant number of men who are infected with the human immunodeficiency virus (HIV) have low testosterone levels. Androgen deficiency in HIV-infected patients is associated with decreased muscle mass and function, and adverse disease outcome. Administration of replacement doses of testosterone to healthy hypogonadal men augments lean body mass, muscle size, and maximal voluntary strength. Recent studies have shown that physiologic testosterone replacement in HIV-infected men with weight loss who have low testosterone levels can also increase muscle mass and effort-dependent strength. However, further studies are needed to determine whether androgen therapy can improve physical function and health-related outcomes in HIV-infected men.

Specific binding and effects of dehydroepiandrosterone sulfate (DHEA-S) on skeletal muscle cells: possible implication for DHEA-S replacement therapy in patients with myotonic dystrophy

Dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S) are the most abundant steroidal products and major circulating steroids in humans. The serum concentrations of DHEA-S are lower in patients with myotonic dystrophy (DM) than normal controls, and possible improvement of myotonia and muscle weakness was recently reported following DHEA-S replacement therapy. However, the molecular mechanism of action of DHEA-S remains unknown. To understand the reported anti-DM action of DHEA-S, we investigated DHEA-S binding in skeletal muscle cells in vitro. We identified two populations of DHEA-S binding sites (Kd = 5-9 microM and 35-40 microM) in C2C12 myocytes. Similar binding sites were also identified in human skeletal muscles. The Kd value of the high-affinity site was within the range of serum concentrations of DHEA-S in adult humans. Our results suggest that DHEA-S might act directly on skeletal muscles under normal physiological conditions in humans.

Androgen effects on body composition and muscle function: implications for the use of androgens as anabolic agents in sarcopenic states

Testosterone-induced nitrogen retention in castrated male animals, eunuchoidal men, pre-pubertal boys and women, and the sex-related differences in the size of the muscles between male and female animals, have been cited as evidence that testosterone has anabolic effects. Recent studies have reported that replacement doses of testosterone in hypogonadal men and supraphysiological doses in eugonadal men increase fat-free mass, muscle size and strength. These effects have provided the rationale for exploring these anabolic applications in sarcopenic states. Although emerging data demonstrate modest gains in fat-free mass in HIV-infected men given replacement doses of testosterone, we do not know whether testosterone supplementation can produce clinically meaningful changes in muscle function and disease outcome in patients with wasting disorders.

Quadriceps strength and timed motor performances in myotonic dystrophy, Charcot-Marie-Tooth disease, and healthy subjects

BACKGROUND AND PURPOSE

The leading hypothesis was that a relation exists between muscular strength and functional abilities. Therefore a study was undertaken to quantify such a relationship in a population of subjects with different muscular strengths. This population consisted of healthy subjects and subjects with slowly progressive neuromuscular disorders.

METHODS

The study included 33 patients with myotonic dystrophy, 29 patients with Charcot-Marie-Tooth disease and 20 healthy subjects. Isokinetic and isometric knee torques were measured on an isokinetic dynamometer at various velocities. The following activities were timed: descending and ascending stairs, rising from a chair, rising from supine, walking at natural speed and walking at maximum speed.

RESULTS

The population covered a wide range of the variables: whereas the healthy subjects performed best (i.e. had the highest knee torques and performed the activities most quickly), the myotonic dystrophy group included the subjects with the lowest knee torques. The natural logarithms (In) of isokinetic extension torque at the highest velocity (120 degrees/s) and those of the time taken to perform the described activities showed the highest levels of correlation. It was found that after correction for age and weight, 56% (walking at natural speed) to 73% (descending stairs) of the variance in the In of the time taken could be attributed to the variance in the In of the torques.

CONCLUSION AND DISCUSSION

A strong relation between quadriceps strength and timed motor performances were demonstrated. The impact of strength reduction on time taken was most obvious in subjects with considerably decreased strength. Therefore, it is feasible to try to influence muscle strength in patients with relevant strength reduction in order to achieve better functional ability.

Carrell-Krusen Symposium Invited Lecture-1997. Myotonic disorders in childhood: diagnosis and treatment

The recent discoveries that mutations in the genes for the skeletal muscle sodium and chloride channels are responsible, respectively, for paramyotonia/hyperkalemic periodic paralysis and for myotonia congenita of Thomsen have made the classification, diagnosis, and treatment of these disorders much easier. The discovery that myotonic dystrophy results from an unstable [CTG]n trinucleotide expansion has permitted the accurate diagnosis of both symptomatic and asymptomatic individuals, and has led to major advances in preventive treatment, including prenatal and genetic counseling. Diseases that resemble the inherited myotonic disorders are now easier to identify, and as a result of genetic testing a new clinical disorder that is similar to but distinct from myotonic dystrophy has emerged. This new disorder, proximal myotonic myopathy, does not appear to be linked to the genes for the sodium or chloride channels, and has cataracts, myotonia, weakness, and no abnormal expansion of the [CTG]n repeat in the gene for myotonic dystrophy. This review discusses the diagnosis and treatment of these myotonic disorders.

The hormonal control of protein metabolism

While all the hormones described have regulatory effects on the rates of protein synthesis and breakdown there is a complex interaction between them in this control process. Insulin, GH and IGF-I play a dominant role in the day-to-day regulation of protein metabolism. In humans insulin appears to act primarily to inhibit proteolysis while GH stimulates protein synthesis. In the post-absorptive state IGF-I has acute insulin-like effects on proteolysis but in the fed state, or when substrate is provided for protein synthesis in the form of an amino acid infusion, IGF-I has been shown to stimulate protein synthesis. Growth hormone and testosterone have an important role during growth but continue to be required to maintain body protein during adulthood. Thyroid hormones are also required for normal growth and development. The hormones glucagon, glucocorticoids and adrenaline are all increased in catabolic states and may work in concert to increase protein breakdown in muscle tissue and to increase amino acid uptake in liver for gluconeogenesis. While increased glucocorticoids result in reduced muscle mass the effects of glucagon may be predominantly in the liver resulting in increased uptake of amino acids. In contrast to the catabolic effect of adrenaline on glucose and lipid metabolism, studies to date suggest that adrenaline may have an anti-catabolic effect on protein metabolism. Despite this adrenaline increases the production of the gluconeogenic amino acid alanine by muscle and its uptake by the splanchnic bed. There is considerable interest in the use of anabolic hormones, either alone or in combination, in the treatment of catabolic states. GH combined with insulin has been shown to improve whole-body and skeletal muscle kinetics while GH combined with IGF-I has a greater positive effect on protein metabolism in catabolic states than either hormone alone. If catabolic states are to be treated successfully a greater understanding of the role of the catabolic hormones in these states and the possible treatment of these states with anabolic hormones is required.

Testosterone therapy and the pathogenesis of Kennedy's disease (X-linked bulbospinal muscular atrophy)

The mutation in X-linked bulbospinal muscular atrophy (XBSMA) is an increased CAG triplet repeat coding for a polyglutamine domain in the gene for the androgen receptor. This might impair the effect of testosterone on motor neurons, leading to their progressive degeneration. We report a trial of high-dose oral testosterone therapy in two brothers with XBSMA. Patient 1 received 37.5 mg of testosterone daily for more than 18 months, and Patient 2 received 25 mg per day for six months, both in combination with exercise therapy. Patient 1 showed improvement of up to 300% in muscle work output. Patient 2, who did less exercise, had no symptomatic improvement. These results indicate that exogenous testosterone therapy is not harmful, and may produce functional improvement when combined with exercise. We hypothesize that high-dose testosterone may reduce a toxic gain of function that the mutation produces, perhaps by inhibiting glutamate neurotoxicity.

Clinical and hormonal aspects of male hypogonadism in myotonic dystrophy

In order to study male hypergonadotropic hypogonadism as completely as possible, and to evaluate its possible effects on muscle atrophy and sexuality, RIA or IRMA methods were used to measure the levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, total (T) and free (FT) testosterone, estradiol (E), dihydrotestosterone (DHT), sex hormone binding globulin (SHBG), androstenedione (A) and 17-OH-progesterone (17-OH-P) in 29 patients with myotonic dystrophy (MD). The mean hormonal levels +/-SD were: LH 8.0 +/- 4.4 mIU/ml, FSH 17.4 +/- 11.5 mIU/ml, A 200 +/- 130 ng/dl (all higher than in controls); T 406 +/- 290 ng/dl, FT 22.7 +/- 7.0 pg/ml, DHT 55.5 +/- 29.7 ng/ml (all lower than in controls). The low FT and DHT levels (never previously studied in MD) confirm the androgenic deficiency. The high androstenedione levels and low testosterone concentrations suggest defective enzyme 17-dehydrogenase. The duration of the disease correlated with both testosterone (r = -0.56) and FT levels (r = -0.59), showing that hypogonadism tends to worsen progressively. When the patients were divided into three groups on the basis of the severity of muscle involvement (A, B and C), LH and FSH levels were higher in group C (more severe disease) than in group A, respectively 9.3 +/- 4.7 and 20.6 +/- 12.3 mIU/ml versus 4.8 +/- 0.9 and 8.4 +/- 3.8, p < 0.03; T levels were lower in group C than in group A, 337.3 +/- 263.4 ng/dl versus 649.7 +/- 320.3 (p < 0.03); however, there was no significant difference in the FT levels of the three groups, which may imply that hypogonadism is unlikely to have a direct effect on muscle atrophy. About 25% of our patients were impotent; these subjects had higher LH and FSH (p < 0.001) and lower FT levels than the patients who were not impotent (p < 0.03). However, hypogonadism may not be the only cause of impotence as all of the impotent patients belonged to group C and had a very high (CTG)n triplet expansion. We hypothesise that hypogonadism and sexual impairment could be partially due to a muscle cell alteration: i.e. a dysfunction of both the testicular peritubular myoid cells and of the corpus cavernosum smooth muscle.

Measurement, nature, and implications of skeletal muscle strength in patients with neurological disorders

Muscle strength is frequently impaired in patients with neurological disorders. Numerous instrumented and non-instrumented options exist for measuring the strength of such patients. Such measurements are useful for clarifying patient status and documenting changes over time. Moreover the measurements are often informative of present or future function among a variety of diagnostic groups. Measurements of muscle strength are an essential component of the neurological evaluation and provide information of substantial importance to clinical care.

Quantitation of muscle mass and muscle protein synthesis rate: documenting a response to myoblast transfer

Initial trials of myoblast transfer into individual muscles should include studies of regional muscle mass. Magnetic resonance imaging is a safe and accurate technique that should be studied in the context of these trials. Creatinine excretion should also be measured in order to provide baseline information for future studies of myoblast injections into a larger number of muscles. In vivo assessment of muscle protein synthesis can be combined with histologic study to determine if the treatment alters the rate of protein synthesis.

Functional testing

Functional testing is useful to monitor the natural history of several neuromuscular disorders, and to measure the efficacy of therapeutic agents in clinical trials. A major limitation of functional testing is that a single test is often not appropriate throughout all stages of disease. The same limitation holds true for other measurements of disease progression. MMT and quantitative myometry become technically difficult to perform and lack sensitivity to disease progression at some stages in the course of DMD, ALS, and spinal muscular atrophy. Other limitations of functional testing are its lack of sensitivity to detect a subtle improvement or decline in muscle strength, and the difficulty of applying standard statistical methods to analyze disease progression or therapeutic efficacy. The advantages of functional testing outweigh the limitations. Function testing uses daily activities to monitor disease progression. Patient's appreciate improvements in function more readily than improvements in muscle strength. Functional testing is easily standardized and is reliable. It can be performed, with little or no expense, in almost any clinical setting. The primary challenge for investigators who wish to incorporate functional tests is to identify functional tests that best measure the natural history of the specific disease under investigation. Further, functional testing allows the clinician to provide an educated guess on the likely future course of disease.