A novel missense mutation in the caveolin-3 gene in rippling muscle disease

The spectrum of rippling muscle disease

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.

Caveolinopathies: translational implications of caveolin-3 in skeletal and cardiac muscle disorders

Caveolae are specialized lipid rafts localized on the cytoplasmic surface of the sarcolemmal membrane. Caveolae contribute to the maintenance of plasma membrane integrity, constitute specific macromolecular complexes that provide highly localized regulation of ion channels, and regulate vesicular trafficking and signal transduction. In skeletal muscle, the main structural assembly of caveolae is mediated by caveolin-3. Another family of adapter proteins, the cavins, is involved in the regulation of caveolae function and in the trafficking of caveolin-derived structures. Caveolin-3 defects lead to four distinct skeletal muscle disease phenotypes: limb-girdle muscular dystrophy, rippling muscle disease, distal myopathy, and hyperCKemia. Many patients show an overlap of these symptoms, and the same mutation can be linked to different clinical phenotypes. An ever-growing interest is also focused on the association between caveolin-3 mutations and heart disorders. Indeed, caveolin-3 mutants have been described in a patient with hypertrophic cardiomyopathy and two patients with dilated cardiomyopathy, and mutations in the caveolin-3 gene (CAV3) have been identified in patients affected by congenital long QT syndrome. Although caveolin-3 deficiency represents the primary event, multiple secondary molecular mechanisms lead to muscle tissue damage. Among these, sarcolemmal membrane alterations, disorganization of skeletal muscle T-tubule network, and disruption of distinct cell signaling pathways have been determined.

Caveolinopathies: from the biology of caveolin-3 to human diseases

In muscle tissue the protein caveolin-3 forms caveolae--flask-shaped invaginations localized on the cytoplasmic surface of the sarcolemmal membrane. Caveolae have a key role in the maintenance of plasma membrane integrity and in the processes of vesicular trafficking and signal transduction. Mutations in the caveolin-3 gene lead to skeletal muscle pathology through multiple pathogenetic mechanisms. Indeed, caveolin-3 deficiency is associated to sarcolemmal membrane alterations, disorganization of skeletal muscle T-tubule network and disruption of distinct cell-signaling pathways. To date, there have been 30 caveolin-3 mutations identified in the human population. Caveolin-3 defects lead to four distinct skeletal muscle disease phenotypes: limb girdle muscular dystrophy, rippling muscle disease, distal myopathy, and hyperCKemia. In addition, one caveolin-3 mutant has been described in a case of hypertrophic cardiomyopathy. Many patients show an overlap of these symptoms and the same mutation can be linked to different clinical phenotypes. This variability can be related to additional genetic or environmental factors. This review will address caveolin-3 biological functions in muscle cells and will describe the muscle and heart disease phenotypes associated with caveolin-3 mutations.