Association between bone mineral density, muscle strength, and vitamin D status in patients with myasthenia gravis: a cross-sectional study

Causal effect of vitamin D on myasthenia gravis: a two-sample Mendelian randomization study

Introduction

Observational studies suggest that vitamin D supplementation may be effective in preventing myasthenia gravis (MG). However, the causal relationship between circulating vitamin D levels and MG remains unclear. This study aimed to examine the genetic causality of circulating vitamin D and MG using data from large population-based genome-wide association studies (GWAS).

Methods

SNPs (single nucleotide polymorphisms) strongly associated with exposure were selected. Two-sample Mendelian Randomization (MR) was performed with inverse variance weighting (IVW), MR-Egger (Mendelian randomization-Egger), weight median and MR-PRESSO (Mendelian randomization pleiotropy residual sum and outlier) methods. Heterogeneity was tested via IVW and MR-Egger. Pleiotropy was tested using MR-Egger intercept test and MR-PRESSO method. MR-PRESSO was also used to detect outliers. Leave-one-out analysis was used to identify SNPs with potential effect. Reverse MR analysis was also performed.

Result

In IVW, circulating vitamin D levels had no causal effect on MG [OR = 0.91 (0.67-1.22), p = 0.532] and MG had no causal effect on circulating vitamin D [OR = 1.01 (099-1.02), p = 0.663]. No heterogeneity or pleiotropy was observed (p > 0.05). Other MR methods also agreed with IVW results.

Conclusion

This study provides the causal relationship between genetically predicted circulating vitamin D levels and MG and provides new insights into the genetics of MG.

Gut microbiota and calcium balance

Microorganisms living on the surface and inside the human body play an important role in the physiological activities of the human body. The largest microecosystem in the human body is the gut microbiome. Calcium disorders are found in many diseases. For example, patients with chronic renal insufficiency present with secondary hyperparathyroidism, which is caused by a calcium imbalance in the body. In addition, calcium dysregulation may affect lipid metabolism in the liver through the calmodulator pathway, leading to cirrhosis, etc. Currently, a considerable number of probiotics have been proven to enhance the body's absorption of calcium. This paper reviews the effects of intestinal flora and related factors such as short-chain fatty acids, estrogen, immune factors and vitamin D on calcium balance.

Evaluation of the Quantitative Myasthenia Gravis Score and Grip Strength in Chinese Patients With Myasthenia Gravis: An Observational Study

Introduction: The quantitative myasthenia gravis score is a commonly used scale for evaluating muscle weakness associated with myasthenia gravis (MG). It has been reported that some items used in the scale have low discriminative properties. However, there has been no research investigating the applicability of the quantitative MG score (QMGS) in Chinese patients with MG. In addition, the scoring method and ranges of grip strength items in QMGS need to be further evaluated.

Methods: This study included 106 Chinese patients with MG, enrolled between September 2020 and February 2021, who were evaluated using the QMGS. Each item in the QMGS was analyzed for distribution. Three methods of evaluating grip strength, grip strength decrement, maximum grip strength, and relative grip strength, were compared. The correlation between the QMG total score minus grip strength score, and three evaluating methods, was analyzed.

Results: The grip strength, swallowing, speech, diplopia, ptosis, and facial muscles items showed a clustered distribution. Most patients (94%) presented their maximum grip strength in the first four grip strength measurements. The QMG total score minus the grip strength score had a weak correlation with grip strength decrement (R grip r = 0.276; L grip r = 0.353, both p < 0.05) and moderate correlations with maximum grip strength (R grip r = −0.508; L grip r = −0.507; both p < 0.001) and relative grip strength (R grip r = −0.494; L grip r = −0.497, both p < 0.001).

Conclusions: This study suggested that partial items in the QMGS have low discriminative properties for Chinese populations and the maximum grip strength value is the better method to evaluate grip strength compared to the other two scoring methods. Based on the quartiles of maximum grip strength, we propose new scoring ranges for the grip strength items.

Low Vitamin D Serum Levels in a Cohort of Myasthenia Gravis Patients in Argentina

There are limited and controversial studies that address the role of vitamin D (vitD), a vitamin with immunomodulatory effects, in myasthenia gravis (MG), a neuromuscular autoimmune disease. We aimed to assess 25-hydroxy vitamin D (25(OH)D) levels and to evaluate possible associations with the clinical severity and other biomarkers of the disease. Serum levels of 25(OH)D, anti-acetylcholine receptor antibodies and complement factor C5a were measured in MG patients (n = 66) and healthy volunteers (HV) (n = 25). Participants were evaluated through questionnaires to determine vitD intake and sunlight exposure. Severity scores were registered for MG patients. We found an 89.4% of MG individuals with nonsufficient levels of vitD, in comparison with 68.0% in the group of HV (OR = 3.96; P = 0.024). In addition, there was an inverse correlation between 25(OH)D levels and one of the scores (P = 0.037 r = -0.26, CI₉₅  = -0.49 to -0.0087). However, when we compared 25(OH)D median serum levels between MG patients and HV, no statistically significant differences have been found. This is the first report of vitD status in a cohort of Argentinean MG patients, where we found that patients are more likely to have nonsufficient levels of vitD compared to healthy people and that patients with more severe disease have lower levels of vitD.

Neuromuscular Diseases and Bone

Neuromuscular diseases (NMDs) are inherited or acquired conditions affecting skeletal muscles, motor nerves, or neuromuscular junctions. Most of them are characterized by a progressive damage of muscle fibers with reduced muscle strength, disability, and poor health-related quality of life of affected patients. In this scenario, skeletal health is usually compromised as a consequence of modified bone-muscle cross-talk including biomechanical and bio-humoral issues, resulting in increased risk of bone fragility and fractures. In addition, NMD patients frequently face nutritional issues, including malnutrition due to feeding disorders and swallowing problems that might affect bone health. Moreover, in these patients, low levels of physical activity or immobility are common and might lead to overweight or obesity that can also interfere with bone strength features. Also, vitamin D deficiency could play a critical role both in the pathogenesis and in the clinical scenario of many NMDs, suggesting that its correction could be useful in maintaining or enhancing bone health, especially in the early phases of NMDs. Last but not least, specific disease-modifying drugs, available for some NMDs, are frequently burdened with adverse effects on bone tissue. For example, glucocorticoid therapy, standard of care for many muscular dystrophies, prolongs long-term survival in treated patients; nevertheless, high dose and/or chronic use of these drugs are a common cause of secondary osteoporosis. This review addresses the current state of knowledge about the factors that play a role in determining bone alterations reported in NMDs, how these factors can modify the biological pathways underlying bone health, and which are the available interventions to manage bone involvement in patients affected by NMDs. Considering the complexity of care of these patients, an interdisciplinary and multimodal management strategy based on both pharmacological and non-pharmacological interventions is recommended, particularly targeting musculoskeletal issues that are closely related to functional independence as well as social implications.

Effects of alendronate and alfacalcidol on bone in patients with myasthenia gravis initiating glucocorticoids treatment

OBJECTIVE

Glucocorticoids (GCs) are the first-line treatment for myasthenia gravis (MG) and act as long-term immunosuppressants. However, GCs can induce osteoporosis and bone fractures. In this study, we evaluate the effects of oral alendronate and alfacalcidol, or alfacalcidol alone on the bone of Chinese patients with MG who will initiate treatment with GCs.

DESIGN AND METHODS

A total of 75 patients were included in this 12-month prospective, open-label, single-centre study. Patients with bone mineral density (BMD) T-score less than -1.0 at baseline were treated with 70 mg of alendronate per week. Patients with BMD T-score greater than -1.0 at baseline were included in the alfacalcidol-alone group. Patients in two groups were treated with 0.25 μg of alfacalcidol every other day and 600 mg of calcium daily.

RESULTS

After 12 months of treatment, the mean BMD of lumbar spine, femoral neck and total hip increased by 3.4% (P = .002), 1.8% (P = .21) and 2.6% (P = .02), respectively, in alendronate group. In alfacalcidol-alone group, the mean BMD of lumbar spine, femoral neck and total hip decreased by 6.1%, 3.2% and 3.3%, respectively (all P < .001 vs baseline).

CONCLUSIONS

We demonstrated for the first time that treatment with alendronate combined with alfacalcidol significantly increased BMD, decreased bone turnover biomarker levels and reduced the occurrence of hypercalciuria in a large cohort of Chinese patients with MG who initiated treatment with glucocorticoids. However, treatment with alfacalcidol alone failed to prevent bone loss in patients with MG receiving glucocorticoid therapy.