Abstract

The aim of this review is to summarize and discuss recent findings and new insights in the etiology and phenotype of metabolic myopathies. The review relies on a systematic literature review of recent publications. Metabolic myopathies are a heterogeneous group of disorders characterized by mostly inherited defects of enzymatic pathways involved in muscle cell metabolism. Metabolic myopathies present with either permanent (fixed) or episodic abnormalities, such as weakness, wasting, exercise-intolerance, myalgia, or an increase of muscle breakdown products (creatine-kinase, myoglobin) during exercise. Though limb and respiratory muscles are most frequently affected, facial, extra-ocular, and axial muscles may be occasionally also involved. Age at onset and prognosis vary considerably. There are multiple disease mechanisms and the pathophysiology is complex. Genes most recently related to metabolic myopathy include PGM1, GYG1, RBCK1, VMA21, MTO1, KARS, and ISCA2. The number of metabolic myopathies is steadily increasing. There is limited evidence from the literature that could guide diagnosis and treatment of metabolic myopathies. Treatment is limited to mainly non-invasive or invasive symptomatic measures. In conclusion, the field of metabolic myopathies is evolving with the more widespread availability and application of next generation sequencing technologies worldwide. This will broaden the knowledge about pathophysiology and putative therapeutic strategies for this group of neuromuscular disorders.

Highlights

  • IntroductionMetabolic myopathies (MMs) are a heterogeneous group of metabolic disorders characterized by defects of enzymatic pathways involved in myocyte metabolism (inborn errors of metabolism) [1]

  • Metabolic myopathies (MMs) are a heterogeneous group of metabolic disorders characterized by defects of enzymatic pathways involved in myocyte metabolism [1].MMs can affect the skeletal muscle exclusively, or the muscle plus other organs or tissues (metabolic myopathy plus (MM+), collateral myopathy)

  • This review focuses on recently detected abnormal metabolic pathways associated with MM or MM+ and new insights into MMs due to impairment of known established metabolic pathways

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Summary

Introduction

Metabolic myopathies (MMs) are a heterogeneous group of metabolic disorders characterized by defects of enzymatic pathways involved in myocyte metabolism (inborn errors of metabolism) [1]. MMs can affect the skeletal muscle exclusively, or the muscle plus other organs or tissues (metabolic myopathy plus (MM+), collateral myopathy). The limb muscles are predominantly affected in MM, but facial, extraocular, axial, and respiratory muscles may be involved [1]. MMs/MMs+ are heterogeneous hereditary disorders resulting from multiple mechanisms of disease and complex pathophysiologies. A number of additional defective pathways have been detected, which may phenotypically manifest as MM/MM+. This review focuses on recently detected abnormal metabolic pathways associated with MM or MM+ and new insights into MMs due to impairment of known established metabolic pathways

Clinical Presentation
MM due to Impaired Carbohydrate Metabolism
MMs due to Impaired Lipid Metabolism
Coenzyme-Q Deficiency and Myopathy
Others
Carbohydrate Metabolism
Lipid Metabolism
Mitochondrial Disorders
Treatment
Lysosomal Storage Diseases
Findings
Conclusions
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