Reduced adrenal androgens in patients with 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.

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.

Towards an integrative approach to the management of myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common type of muscular dystrophy in adults. Approximately 60% of individuals report either having difficulty performing or being unable to carry out some activities related to home management, mobility and transportation, work and leisure. Employment, educational level and income are, on average, lower than in the general population. The complexity and variability of disease manifestations in DM1 undoubtedly pose a challenge as regards anticipating all potential problems and developing a plan for health and community management. This article presents a conceptual model for DM1 management as well as a brief discussion of an approach for developing interdisciplinary health and community services.

The effect of dehydroepiandrosterone sulfate (DHEAS) on myotonia: intracellular studies

OBJECTIVE

In order to find some appropriate medicine to suppress myotonia without decreasing muscle strength experiments were performed on myotonic (mto) mice whose Cl channel does not develop due to stop codon and serves as an animal model of myotonia. In myotonic dystrophy dehydroepiandrosterone is low in the serum and it has been reported that intravenous injections of DHEAS to human cases improves myotonia and activities of daily living.

MATERIALS AND METHODS

Three pairs of heterozygote mto mice, SWR/J-Clcn1(adr-mto/+) and ten Wistar rats were used. We performed intracellular recordings of myotonia from mto mice and the drug effects on insertion myotonia were recorded from the hemidiaphragm preparations of mto mice with different concentrations of DHEAS. Isometric twitch tension was recorded from rat hemidiaphragm preparations in Tyrode's solution and the effect of DHEAS on the muscle twitch tension was measured at different concentrations of DHEAS from 100 mg/l to 300 mg/l. The effect of mexiletine on ITT was also measured.

RESULTS

In mto mice insertion myotonia was recorded as soon as the microelectrode was inserted in the muscle cells. When DHEAS was added to Tyrode's solution, insertion myotonia was suppressed. DHEAS decreased ITT up to 70% of the original value, though mexiletine decreased ITT to 30% of the original value. Therefore, the decrement of the muscle strength in DHEAS solution is much smaller than that of mexiletine.

CONCLUSION

Since myotonic dystrophy shows progressive muscle weakness in addition to myotonia, medications like DHEAS are more favorable than the typical Na channel blocker.

Three cases of androgen-dependent disease associated with myotonic dystrophy

Three cases of androgen-dependent disease in females with myotonic dystrophy are described. Serum androgens in individuals affected by myotonic dystrophy are known to be lower on average than in normal controls. Despite this these three females developed diseases that are androgen dependent, including acne, hidradenitis suppurativa, androgenetic alopecia and keratosis pilaris. These cases support the hypothesis that the peripheral response to androgens rather than absolute circulating levels of androgens is important in androgen-dependent conditions.

Hyperkalaemia and selective hypoaldosteronism in myotonic dystrophy

Myotonic dystrophy (MyD) is a common genetic neuromuscular disorder in which chromosome 19 gives rise to an abnormal expansion of CTG-trinucleotide repeats. MyD is a highly variable multisystem disorder with muscular and nonmuscular abnormalities. Increasingly, endocrine abnormalities, such as gonadal, pancreatic, and adrenal dysfunction are being uncovered. Herein we present three unrelated cases with MyD with abnormally elevated serum potassium; 2 of the 3 cases presented clinically with cardiac dysrhythmias. Hyperkalaemic conditions such as renal failure, cortisol deficiency, pseudohyperkalaemia, and hyperkalaemic periodic paralysis were excluded. Further endocrine evaluation revealed baseline hypoaldosteronism associated with elevated renin activity. Perturbation of the renin-angiotensin-aldosterone system resulted in appropriately enhanced renin activity but with a subnormal aldosterone response, which appeared to be due to adrenal hyporesponsiveness. The treatment of all cases with fludrocortisone was without effect. Whether the apparent mineralocorticoid abnormality in MyD is due to associated hormonal perturbations (i.e. excessive ACTH responsiveness. elevated cytokines, elevated atrial natriuretic hormone, etc.), adrenal atrophy, and/or a manifestation of the underlying kinase dysfunction is uncertain, but merits further evaluation in view of the clinical consequence of hyperkalaemia.

Novel approaches to treat muscular dystrophies

Muscular dystrophies (MD) are a clinically and genetically heterogeneous group of skeletal muscle-wasting diseases. Mutations in the dystrophin gene result in dystrophin deficiency, which constitutes the pathogenic basis of Duchenne and Becker MD (DMD and BMD). Several MD are caused by mutations in other recently identified genes coding for proteins linked to the sarcolemma, the nuclear envelope or the contractile apparatus. In addition, several MD have been mapped to different chromosomal loci and for most of them, the identification of the molecular defect is underway. The immediate result is an ongoing reclassification of the MD into disorders defined not by clinical characteristics but specific genetic mutations. At present, therapy of MD is based on symptomatic treatment and supportive care. Convincing evidence for clinical efficacy is only available for corticosteroids that also suffer from frequent and severe side effects. Up to now, curative therapy is not available, although promising new molecular therapies are under investigation in animal models of MD. Current treatment strategies are discussed and a perspective for effective molecular therapy is given.

Abnormal cytokine and adrenocortical hormone regulation in myotonic dystrophy

Metabolic-endocrine dysfunctions, including hyperinsulinemia, hypertriglyceridemia, increased fat mass, and dysregulation of the hypothalamic-pituitary-adrenal axis, are common in myotonic dystrophy (MD). We hypothesized that increased production of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) may be important underlying mechanisms. We studied the diurnal rhythmicity of cytokines and cortisol, ACTH, and dehydroepiandrosterone in 18 men with adult onset MD and 18 controls. Morning levels of androstenedione, 17-hydroxyprogesterone, testosterone, and insulin were also determined. Genetic analyses were performed, including calculation of allele sizes. Median circulating 24-h levels of IL-6 (P < 0.001), TNF-alpha (P = 0.05), ACTH (P < 0.05), and cortisol (P < 0.05) were all significantly increased in MD, whereas dehydroepiandrosterone levels were decreased (P < 0.001). The diurnal rhythms of these cytokines/ hormones were disturbed in patients. Morning testosterone levels were decreased and insulin levels increased (P < 0.01 for both). Patients with high body fat mass had significantly increased insulin levels and decreased morning levels of cortisol, ACTH, and testosterone. IL-6 and TNF-alpha levels are increased and adrenocortical hormone regulation is disturbed in MD. Adiposity may contribute to these disturbances, which may be of importance for decreased adrenal androgen hormone production and metabolic, muscular, and neuropsychiatric dysfunction in MD.

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.

Dehydroepiandrosterone and Melatonin: Two Neurohormones

Complementary or alternative medicines in the United States have received prominent attention during recent years. Though there seems to be little rigorous support for the long-term efficacy and safety of these treatments in humans,1-2 the popularity of these natural products persists. It has been estimated that, for 1997, 12 percent of the U.S. population (approximately 24 million people) had used herbal medicines within the previous 12 months, and that 5 billion dollars had been spent on these products during that same year.3 Two of the alternative medicines included are dehydroepiandrosterone (DHEA) and melatonin. DHEA is a hormone produced primarily by the adrenal glands, and is a precursor for endogenous steroid production (e.g., testosterone, estrogen). DHEA is also believed to exert central pharmacologic effects. Melatonin is a hormone produced by the pineal gland and is involved in circadium rhythm maintenance and sleep regulation. Because of extensive physiological effects, these two neuro-hormones are being advocated for the treatment of several medical disorders, as well as for routine ailments. The purpose of this article is to discuss salient, pharmacotherapeutic-related characteristics of each hormone, and to briefly review supporting evidence from studies using human subjects.

Androgen response to hypothalamic-pituitary-adrenal stimulation with naloxone in women with myotonic muscular dystrophy

Myotonic muscular dystrophy (MMD) is a disease of autosomal dominant inheritance characterized by multisystem disease, including myotonia, muscle-wasting and weakness of all muscular tissues, and endocrine abnormalities attributed to a genetic abnormality causing a defective cAMP-dependent kinase. We have previously reported that MMD patients demonstrate ACTH hypersecretion after endogenous CRH release stimulated by naloxone administration while manifesting a normal cortisol (F) response. Additionally, others have reported a reduced adrenal androgen (AA) response to exogenous ACTH administration in MMD patients. As ACTH stimulates the secretion of both AAs and F, it is possible that the discordant relationship of these hormones in MMD patients results from a defect of adrenocortical ACTH receptor function or postreceptor signaling or subsequent biochemical events. Furthermore, the molecular abnormality seen in MMD patients may suggest that the mechanism underlying the frequently observed discordances in the secretion of glucocorticoids and AAs (e.g. adrenarche, surgical trauma, severe burns, or intermittent glucocorticoid administration) are explainable solely via an alteration in the function of the ACTH receptor or postreceptor signaling. To ascertain whether the responses of F and AAs to endogenous ACTH diverged in this disorder, we prospectively studied the responses of these hormones to naloxone-stimulated CRH release in nine premenopausal women with MMD and seven healthy age and weight-matched control women. After naloxone infusion (125 micrograms/kg, i.v.), blood sampling was performed at baseline (i.e. -5 min) and at 30 and 60 min. In addition to the absolute hormone level at each time, we calculated the net increment (i.e. change) at 30 and 60 min and the area under the curve (AUC) for F, ACTH, dehydroepiandrosterone (DHA), and androstenedione (A4). Consistent with our previous study, MMD patients demonstrated higher ACTH levels at all sampling times except [minud]5 min. AUC analysis revealed the ACTHAUC values were significantly higher in MMD than in control women (457 +/- 346 vs. 157 +/- 123 pmol/min.L; P < 0.03), whereas the FAUC response did not differ between MMD and controls (13860 +/- 3473 vs. 13375 +/- 3465 nmol/min.L; P > 0.5). Despite the greater ACTH secretion, the baseline circulating dehydroepiandrosterone sulfate levels were significantly lower in MMD compared with control women (18 +/- 23 vs. 61 +/- 23 mumol/L; P < 0.002). The serum concentrations of A4 at baseline, 30 min, and 60 min and DHA levels at 30 and 60 min were also significantly lower in MMD vs. control women. Additionally, the A4AUC and DHAAUC values were significantly lower in MMD patients than in controls. Furthermore, the net response of DHA at 60 min to the endogenous ACTH increase was also reduced in MMD patients compared with that in control subjects (2.3 +/- 2.1 vs. 5.6 +/- 2.6 nmol/L; P < 0.02). In conclusion, in addition to ACTH hypersecretion to CRH-mediated stimuli, these data suggest that MMD patients have a defect in the adrenocortical response to ACTH, reflected in normal F and reduced DHA and A4 secretion. Whether this defect is inherent to the disease or simply reflects adaptive changes to chronic disease remains to be demonstrated. However, it is possible that further studies of the response of MMD patients to ACTH may reveal a mechanism that explains the frequently observed dichotomy in the secretion of glucocorticoids and AAs.

Effect of exogenous arginine vasopressin on adrenocorticotropin and cortisol release in myotonie dystrophy patients: delayed responses of normal magnitude

Abstract We administered intramuscular arginine vasopressin (AVP) to ten normal controls and eight myotonic dystrophy patients. By measuring plasma AVP levels in five of the myotonics and all the normals, we showed that absorption and distribution of AVP was not delayed or significantly reduced in myotonics. The magnitude of the mean plasma adrenocorticotropin (ACTH) response to AVP in the myotonics was not different from that of normals, although it was significantly delayed (mean peak time, 37.5+/-4.9 versus 17.0 +/- 3.2 min). We propose that this delay was caused by a significantly reduced ACTH secretion rate in myotonics, because the maximum rate of detection of ACTH in plasma is reduced in myotonics (0.6 +/- 0.2 versus 1.7 +/- 0.5 pmol/L/min), whose corticotropes, while having the same capacity to respond to the AVP stimulus, are slower to attain that capacity. The mean integrated cortisol response (AUC) was significantly smaller for myotonics (8072 +/- 2017 versus 13049+/-1630 nmol.min/L). This may be due to the slower rate of ACTH delivery to the adrenal in myotonics. The timing of the adrenal response does not appear to be impaired in myotonic dystrophy, with the cortisol peak following the ACTH peak by approximately 15 min in both groups. The normal magnitude ACTH response to AVP in myotonics is in contrast to that seen to ACTH secretagogues acting via corticotropin- releasing hormone-initiated pathways, where a rapid hypersecretion is seen. We propose a mechanism of defective calcium transport to account for these observations.

Adrenocorticotropin hyperresponsiveness in myotonic dystrophy following oral fenfluramine administration

Abstract The plasma immunoreactive adrenocorticotropin and cortisol responses to oral fenfluramine hydrochloride (1.5mg/kg body wt) or placebo were examined in 11 patients with myotonic dystrophy, 4 controls with facioscapulohumeral dystrophy, a similarly debilitating muscle wasting disease, and 14 normal controls in single-blind studies performed in mid-afternoon. Mean areas under the adrenocorticotropin response versus time curve were significantly greater in myotonics (2573 + 429 pmol.min/L) than in facioscapulohumeral dystrophy controls (696 + 279 pmol.min/L, P<0.02) and normals (560+/-61 pmol.min/L, P<0.0001). Corresponding cortisol responses were significantly greater in myotonics (35757 + 3949 nmol.min/L) than in normals (21828+/-1669 nmol.min/L, P < 0.001), but not significantly greater than those in facioscapulohumeral dystrophy controls (22830 + 6140 nmol.min/L, P = 0.055). No stressful side-effects which could affect hormone responses, and no significant changes in blood pressure or heart rate were noted. Fenfluramine activates central serotonergic and/or noradrenergic pathways initiating secretion of corticotropin-releasing hormone and possibly arginine vasopressin. We postulate that these fenfluramine-activated pathways are hyperstimulated in myotonics, leading to adrenocorticotropin and cortisol hypersecretion. This may be a manifestation of a general cell membrane defect in myotonic dystrophy. We found a lack of correlation of age (and severity of disease) with adrenocorticotropin response in myotonics, and therefore, the hyperresponse may serve as a useful marker for the disease before development of other overt signs.

Immaturity of muscle fibers in the congenital form of myotonic dystrophy: its consequences and its origin

Skeletal muscle maturation is impaired in children with congenital myotonic dystrophy. This immaturity is characterized at the light microscopy level by an abnormal presence of myotubes, small fascicles of muscle fibers, thin myofibers, and delayed muscle fiber type differentiation with a peripheral halo lacking mitochondrial oxidative enzyme activity. At an ultrastructural level, the characteristics are a paucity of myofibrils with a peripheral rim devoid of mitochondria and myofibrils in the fibers. In time the muscle is able to gain a certain degree of maturity as shown in one of our cases who had two successive muscle biopsies. The muscle, however, never becomes normal but retains discrepancies in fiber size and fiber type distribution and shows some fiber necrosis. Maturation of the motoneurons is normal, which may explain necrosis of immature muscle fibers. In an experimental study carried out to look for evidence of a circulatory factor in mothers of children with congenital myotonic dystrophy, it was found that sera from these mothers administered intra-peritoneally to newborn rats does in fact impair muscle maturation, whereas rats injected similarly with sera from control women showed normal muscle maturation.

Effect of testosterone on muscle protein synthesis in myotonic dystrophy

Muscle wasting in myotonic dystrophy may result from decreased muscle anabolic processes rather than from increased catabolism. Male patients with myotonic dystrophy often have low levels of circulating androgens, and androgen administration has been shown to increase their muscle mass. We have studied the effect of testosterone enanthate administration (3 mg/kg weekly for 3 months) on muscle and whole body protein synthesis in 6 male patients with myotonic dystrophy. Muscle protein synthesis was estimated from the rate of isotope incorporation into muscle protein obtained by quadriceps muscle biopsy during a primed continuous infusion of L-[1-13C]leucine. Testosterone administration resulted in a significant increase in muscle protein synthesis in all patients. Whole body protein synthesis did not increase, indicating that protein synthesis in other tissues may have declined. Muscle ribonucleic acid content rose significantly in response to testosterone administration, suggesting that testosterone initiated its effect by hormone receptor interaction with muscle nuclei.