Truncation of Caveolin-3 causes autosomal-recessive Rippling Muscle Disease

Population-based genetic effects for developmental stuttering

Despite a lifetime prevalence of at least 5%, developmental stuttering, characterized by prolongations, blocks, and repetitions of speech sounds, remains a largely idiopathic speech disorder. Family, twin, and segregation studies overwhelmingly support a strong genetic influence on stuttering risk; however, its complex mode of inheritance combined with thus-far underpowered genetic studies contribute to the challenge of identifying and reproducing genes implicated in developmental stuttering susceptibility. We conducted a trans-ancestry genome-wide association study (GWAS) and meta-analysis of developmental stuttering in two primary datasets: The International Stuttering Project comprising 1,345 clinically ascertained cases from multiple global sites and 6,759 matched population controls from the biobank at Vanderbilt University Medical Center (VUMC), and 785 self-reported stuttering cases and 7,572 controls ascertained from The National Longitudinal Study of Adolescent to Adult Health (Add Health). Meta-analysis of these genome-wide association studies identified a genome-wide significant (GWS) signal for clinically reported developmental stuttering in the general population: a protective variant in the intronic or genic upstream region of SSUH2 (rs113284510, protective allele frequency = 7.49%, Z = -5.576, p = 2.46 × 10^-8) that acts as an expression quantitative trait locus (eQTL) in esophagus-muscularis tissue by reducing its gene expression. In addition, we identified 15 loci reaching suggestive significance (p < 5 × 10^-6). This foundational population-based genetic study of a common speech disorder reports the findings of a clinically ascertained study of developmental stuttering and highlights the need for further research.

Role of aquaglyceroporins and caveolins in energy and metabolic homeostasis

Aquaglyceroporins and caveolins are submicroscopic integral membrane proteins that are particularly abundant in many mammalian cells. Aquaglyceroporins (AQP3, AQP7, AQP9 and AQP10) encompass a subfamily of aquaporins that allow the movement of water, but also of small solutes, such as glycerol, across cell membranes. Glycerol constitutes an important metabolite as a substrate for de novo synthesis of triacylglycerols and glucose as well as an energy substrate to produce ATP via the mitochondrial oxidative phosphorylation. In this sense, the control of glycerol influx/efflux in metabolic organs by aquaglyceroporins plays a crucial role with the dysregulation of these glycerol channels being associated with metabolic diseases, such as obesity, insulin resistance, non-alcoholic fatty liver disease and cardiac hypertrophy. On the other hand, caveolae have emerged as relevant plasma membrane sensors implicated in a wide range of cellular functions, including endocytosis, apoptosis, cholesterol homeostasis, proliferation and signal transduction. Caveolae-coating proteins, namely caveolins and cavins, can act as scaffolding proteins within caveolae by concentrating signaling molecules involved in free fatty acid and cholesterol uptake, proliferation, insulin signaling or vasorelaxation, among others. The importance of caveolae in whole-body homeostasis is highlighted by the link between homozygous mutations in genes encoding caveolins and cavins with metabolic diseases, such as lipodystrophy, dyslipidemia, muscular dystrophy and insulin resistance in rodents and humans. The present review focuses on the role of aquaglyceroporins and caveolins on lipid and glucose metabolism, insulin secretion and signaling, energy production and cardiovascular homeostasis, outlining their potential relevance in the development and treatment of metabolic diseases.

The role of CAV3 in long-QT syndrome: clinical and functional assessment of a caveolin-3/Kv11.1 double heterozygote versus caveolin-3 single heterozygote

BACKGROUND

Mutations in CAV3, coding for caveolin-3, the major constituent scaffolding protein of cardiac caveolae, have been associated with skeletal muscle disease, cardiomyopathy, and most recently long-QT syndrome (LQTS) and sudden infant death syndrome. We examined the occurrence of CAV3 mutations in a large cohort of patients with LQTS.

METHODS AND RESULTS

Probands with LQTS (n=167) were screened for mutations in CAV3 using direct DNA sequencing. A single proband (0.6%) was found to be a heterozygous carrier of a previously described missense mutation, caveolin-3:p.T78M. The proband was also a heterozygous carrier of the trafficking-deficient Kv11.1:p.I400N mutation. The caveolin-3:p.T78M mutation was found isolated in 3 family members, none of whom had a prolonged QTc interval. Coimmunoprecipitations of caveolin-3 and the voltage-gated potassium channel subunit (Kv11.1) were performed, and the electrophysiological classification of the Kv11.1 mutant was carried out by patch-clamp technique in human embryonic kidney 293 cells. Furthermore, the T-wave morphology was assessed in mutation carriers, double mutation carriers, and nonmutation carriers by applying a morphology combination score. The morphology combination score was normal for isolated caveolin-3:p.T78M carriers and of LQT2 type in double heterozygotes.

CONCLUSIONS

Mutations in CAV3 are rare in LQTS. Furthermore, caveolin-3:p.T78M did not exhibit a LQTS phenotype. Because no association has ever been found between LQTS and isolated CAV3 mutations, we suggest that LQTS9 is considered a provisional entity.

Rippling muscle disease and cardiomyopathy associated with a mutation in the CAV3 gene

Caveolin-3, the myocyte-specific isoform of caveolins, is preferentially expressed in skeletal, cardiac and smooth muscles. Mutations in the CAV3 gene cause clinically heterogeneous neuromuscular disorders, including rippling muscle disease, or cardiopathies. The same mutation may lead to different phenotypes, but cardiac and muscle involvement rarely coexists suggesting that the molecular network acting with caveolin-3 in skeletal muscle and heart may differ. Here we describe an Italian family (a father and his two sons) with clinical and neurophysiological features of rippling muscle disease and heart involvement characterized by atrio-ventricular conduction defects and dilated cardiomyopathy. Muscle biopsy showed loss of caveolin-3 immunosignal. Molecular studies identified the p.A46V mutation in CAV3 previously reported in a German family with autosomal dominant rippling muscle disease and sudden death in few individuals. We suggest that cardiac dysfunction in myopathic patients with CAV3 mutations may be underestimated and recommend a more thorough evaluation for the presence of cardiomyopathy and potentially lethal arrhythmias.

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.