Faculty Bibliography

AIMS: The shRNA-mediated loss of expression of the desmosomal protein plakophilin-2 leads to sodium current (I(Na)) dysfunction. Whether pkp2 gene haploinsufficiency leads to I(Na) deficit in vivo remains undefined. Mutations in pkp2 are detected in arrhythmogenic right ventricular cardiomyopathy (ARVC). Ventricular fibrillation and sudden death often occur in the 'concealed phase' of the disease, prior to overt structural damage. The mechanisms responsible for these arrhythmias remain poorly understood. We sought to characterize the morphology, histology, and ultrastructural features of PKP2-heterozygous-null (PKP2-Hz) murine hearts and explore the relation between PKP2 abundance, I(Na) function, and cardiac electrical synchrony. METHODS AND RESULTS: Hearts of PKP2-Hz mice were characterized by multiple methods. We observed ultrastructural but not histological or gross anatomical differences in PKP2-Hz hearts compared with wild-type (WT) littermates. Yet, in myocytes, decreased amplitude and a shift in gating and kinetics of I(Na) were observed. To further unmask I(Na) deficiency, we exposed myocytes, Langendorff-perfused hearts, and anaesthetized animals to a pharmacological challenge (flecainide). In PKP2-Hz hearts, the extent of flecainide-induced I(Na) block, impaired ventricular conduction, and altered electrocardiographic parameters were larger than controls. Flecainide provoked ventricular arrhythmias and death in PKP2-Hz animals, but not in the WT. CONCLUSIONS: PKP2 haploinsufficiency leads to I(Na) deficit in murine hearts. Our data support the notion of a cross-talk between desmosome and sodium channel complex. They also suggest that I(Na) dysfunction may contribute to generation and/or maintenance of arrhythmias in PKP2-deficient hearts. Whether pharmacological challenges could help unveil arrhythmia risk in patients with mutations or variants in PKP2 remains undefined.

Since the discovery of the genetic bases of the long QT syndrome, several new genetically mediated arrhythmias have been described, defining a new group of syndromes, called inherited arrhythmogenic diseases. This allowed clarifying the substrate of several cases of juvenile sudden death, previously defined as 'idiopathic ventricular fibrillation'. Studies derived from this field also contributed to advance the field of electrophysiology, elucidating some of the mechanisms that regulate the cardiac electrical properties of the heart. Recently, new genes and new proteins have been called into play, expanding the knowledge on the complexity of the regulatory processes modulating the cardiac action potential. Moreover, the collaboration between clinicians and basic scientists opened new approaches in the management of patients affected by genetic arrhythmias. This body of knowledge has then moved into the realization that genetic variations may also influence the predisposition to acquired cardiac diseases. The new exciting challenges that investigators are now facing are connected to the possibility of expanding the field towards the use of these information to shape a newer vision in the management and cure of patients

Introduction: Mutations in the RyR2 cardiac ryanodine receptor are associated with Catecholaminergic POlymorphic Ventricular Tachycardia (CPVT). So far 155 different RyR2 mutations have been rePOrted in patients with clinical manifestations of the disease. Based on the localization of these mutations it has been suggested that screening of the RyR2 gene for diagnostic purPOses should be limited to the regions in which mutations have been rePOrted. In order to assess whether this approach is correct we screened 139 probands from our CPVT cohort and 131 affected family members (AFM) to define whether the limited screening is appropriate. Methods: Open reading frame/splice junction analysis of all the 105 exons of RyR2 was performed by PCR and DNA sequencing. New variants were defined pathogenetic if absent in 400 controls and when they co-segregated with the phenotype in AFM. Results: RyR2 mutations were found in 82/139 probands (59%); all were symptomatic (40/82 survived cardiac arrest). 12/82 (15%) carried mutations outside the regions conventionally screened. 6/82 (7%) probands (all symptomatic and 4 resuscitated from cardiac arrest) had mutations in the 39 exons not screened by a commercial panel of 66/105 exons. Screening of family members in these 6 families identified 3 silent mutation carriers among first degree relatives. Conclusions: Our data show that partial screening of RyR2 in CPVT patients misses a substantial proPOrtion of mutations. Such a partial screening prevents the identification of silent mutation carriers leaving them exPOsed to the risk of life threatening arrhythmias

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease characterized by a structurally normal heart and high lethality beginning in early childhood. The identification of its genetic bases made possible the discovery that arrhythmias are caused by intracellular calcium dysregulation. In the 9 years since the description of the genetic substrate of the disease, we have witnessed remarkable progress in the unraveling of the molecular mechanisms underlying its arrhythmogenesis. The impact of these discoveries extends beyond the field of inherited arrhythmias and sheds new light on the arrhythmogenic mechanisms in some more prevalent diseases characterized by abnormal calcium regulation, such as heart failure. Additionally, basic research studies led to the exploration of new therapeutic strategies with potential clinical impact in the near future in reducing the still high incidence of sudden death associated with these conditions. In the current review, the authors discuss the clinical and genetic features of CPVT, highlighting pathophysiologic insights derived from experimental research and future therapeutic targets.

Introduction: Brugada syndrome (BrS) is a heritable arrhythmogenic disease characterized by an augmented risk of sudden cardiac arrest (SCA). Studies on the pediatric population are few and on a limited number of patients. We describe the natural history of 90 children with BrS and on 48 genotyped patients with BrS, representing the largest series of child carriers of SCN5A mutations reported to date. Methods: 90 children (63 males) clinically and/or genetically affected by BrS, mean 10+/-6y, from 64 different families were studied using retrospective case review. Results: Type I or II ECG was observed in 40 patients (pts); 21 pts had ECG type I and 19 pts had ECG type II; 25 during protocol drug infusion and 5 with fever; 46 pts were studied because carriers of BrS mutations, despite normal ECG. Among the 21 patients with a spontaneous type I ECG, 4 were symptomatic (19%) and among the 19 patients with a spontaneous type II ECG, 5 were symptomatic (26%). 2/25, patients with a drug-induced phenotype were symptomatic (8%). Male predominance was observed in the symptomatic group (boys, 77%; girls, 30%). Family history of SCA was present in 35/90 pts. EP study, performed in 16 pts, was positive in only 1. ICD was implanted in 6 pts. During a mean follow-up of 50+/-34 months, 1 child experienced syncope; all other pts remained asymptomatic. Genetic screening for SCN5A was performed in 32 probands (pbs): 16 were carriers of a genetic defect. 57 pts were studied because of family history of BrS; 52 were carriers of the mutation found in their pbs, 5 belong to families with unknown genotype, but were clinically affected. Conclusions: In the pediatric population, ECG pattern and clinical manifestation of BrS are present in a small percentage of pts, suggesting a more subtle phenotype. Symptoms or ECG pattern can be precipitated by fever. Also, the role of EP study is not conclusive in pediatric BrS. In contrast to adults, some 50% of pediatric pbs are genetically affected, suggesting that a strict clinical selection of pts for SCN5A screening may lead to higher genotyping success