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Rippling Muscle Disease (RMD) is a rare skeletal myopathy characterized by abnormal muscular excitability manifesting with wave-like muscle contractions and percussion-induced muscle mounding. Hereditary RMD is associated with caveolin-3 or cavin-1 mutations. Recently, we identified cavin 4 autoantibodies as a biomarker of immune-mediated RMD (iRMD), though the underlying disease-mechanisms remain poorly understood. Transcriptomic studies were performed on muscle biopsies of 8 patients (5 males; 3 females; ages 26-to-80) with iRMD. Subsequent pathway analysis compared iRMD to human non-disease control and disease control (dermatomyositis) muscle samples. Transcriptomic studies demonstrated changes in key pathways of muscle contraction and development. All iRMD samples had significantly upregulated cavin-4 expression compared to controls, likely compensatory for autoantibody-mediated protein degradation. Proteins involved in muscle relaxation (including SERCA1, PMCA and PLN) were significantly increased in iRMD compared to controls. Comparison of iRMD to dermatomyositis transcriptomics demonstrated significant overlap in immune pathways, and the IL-6 signaling pathway was markedly increased in all iRMD patient muscle biopsies and increased in the majority of iRMD patients’ serum. This study represents the first muscle transcriptomic analysis of iRMD patients and dissects underlying disease mechanisms. Increase of sarcolemmal and cellular calcium channels as well as PLN, an inhibitor of the SERCA pump for calcium into the sarcoplasm, likely alters the calcium dynamics in iRMD. These changes in crucial components of muscle relaxation may underlie rippling by altering calcium flux. Our findings provide crucial insights into the differential expression of genes regulating muscle relaxation and highlight potential disease pathomechanisms. [ABSTRACT FROM AUTHOR]

Rippling muscle disease (RMD) is a rare disorder of muscle hyperexcitability. It is characterized by rippling wave‐like muscle contractions induced by mechanical stretch or voluntary contraction followed by sudden stretch, painful muscle stiffness, percussion‐induced rapid muscle contraction (PIRC), and percussion‐induced muscle mounding (PIMM). RMD can be hereditary (hRMD) or immune‐mediated (iRMD). hRMD is caused by pathogenic variants in caveolin‐3 (CAV3) or caveolae‐associated protein 1/ polymerase I and transcript release factor (CAVIN1/PTRF). CAV3 pathogenic variants are autosomal dominant or less frequently recessive while CAVIN1/PTRF pathogenic variants are autosomal recessive. CAV3‐RMD manifests with a wide spectrum of clinical phenotypes, ranging from asymptomatic creatine kinase elevation to severe muscle weakness. Overlapping phenotypes are common. Muscle caveolin‐3 immunoreactivity is often absent or diffusely reduced in CAV3‐RMD. CAVIN1/PTRF‐RMD is characterized by congenital generalized lipodystrophy (CGL, type 4) and often accompanied by several extra‐skeletal muscle manifestations. Muscle cavin‐1/PTRF immunoreactivity is absent or reduced while caveolin‐3 immunoreactivity is reduced, often in a patchy way, in CAVIN1/PTRF‐RMD. iRMD is often accompanied by other autoimmune disorders, including myasthenia gravis. Anti‐cavin‐4 antibodies are the serological marker while the mosaic expression of caveolin‐3 and cavin‐4 is the pathological feature of iRMD. Most patients with iRMD respond to immunotherapy. Rippling, PIRC, and PIMM are usually electrically silent. Different pathogenic mechanisms have been postulated to explain the disease mechanisms. In this article, we review the spectrum of hRMD and iRMD, including clinical phenotypes, electrophysiological characteristics, myopathological findings, and pathogenesis. [ABSTRACT FROM AUTHOR]