A Mutation in the G-Protein Gene GNB2 Causes Familial Sinus Node and Atrioventricular Conduction Dysfunction.

RATIONALE: Familial sinus node and atrioventricular conduction dysfunction is a rare disorder that leads to paroxysmal dizziness, fatigue, and syncope because of a temporarily or permanently reduced heart rate. To date, only a few genes for familial sinus and atrioventricular conduction dysfunction are known, and the majority of cases remain pathogenically unresolved. OBJECTIVE: We aim to identify the disease gene in a large 3-generation family (n=25) with autosomal dominant sinus node dysfunction (SND) and atrioventricular block (AVB) and to characterize the mutation-related pathomechanisms in familial SND+AVB. METHODS AND RESULTS: Genome-wide linkage analysis mapped the SND+AVB disease locus to chromosome 7q21.1-q31.1 (2-point logarithm of the odds score: 4.64; θ=0); in this region, targeted exome sequencing identified a novel heterozygous mutation (p.Arg52Leu) in the GNB2 gene that strictly cosegregated with the SND+AVB phenotype. GNB2 encodes the ß2 subunit (Gß2) of the heterotrimeric G-protein complex that is being released from G-protein-coupled receptors on vagal stimulation. In 2 heterologous expression systems (HEK-293T cells and Xenopus laevis oocytes), an enhanced activation of the G-protein-activated K+ channel (GIRK; Kir3.1/Kir3.4) was shown when mutant Gß2 was coexpressed with Gγ2; this was in contrast to coexpression of mutant Gß2-Gγ2 with other cardiac ion channels (HCN4, HCN2, and Cav1.2). Molecular dynamics simulations suggested a reduced binding property of mutant Gß2 to cardiac GIRK channels when compared with native Gß2. CONCLUSIONS: A GNB2 gene mutation is associated with familial SND+AVB and leads to a sustained activation of cardiac GIRK channels, which is likely to hyperpolarize the myocellular membrane potential and thus reduces their spontaneous activity. Our findings describe for the first time a role of a mutant G-protein in the nonsyndromic pacemaker disease because of GIRK channel activation.

Exome sequencing identifies a novel heterozygous TGFB3 mutation in a disorder overlapping with Marfan and Loeys-Dietz syndrome.

Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS) are clinically related autosomal dominant systemic connective tissue disorders. Although mutations in several genes of the TGF-beta signalling and related pathways have been identified in the past (e.g. FBN1, TGFBR1, TGFBR2, SMAD3, TGFB2), there are still many individuals with "marfanoid" phenotypes in whom no causative mutations are identified. We performed whole exome sequencing in two of three affected individuals from a family with phenotypic features overlapping MFS and LDS. The two affected children and their affected father had tall stature, arachnodactyly, hyperextensible joints, hypertelorism, bifid uvula, but no cardiac involvement, aortic dilation or eye involvement. We detected a novel heterozygous mutation in TGFB3, c.898C>G, predicting the missense substitution p.Arg300Gly. Sanger sequencing confirmed the mutation and its segregation with the phenotype. The first two TGFB3 mutations were reported previously in two unrelated individuals with marfanoid features: one individual with growth retardation carried a heterozygous loss-of-function mutation (c.1226G>A; p.Cys409Tyr; Rienhoff et al., 2013), whereas a child with overgrowth carried a mutation in the same codon as the mutation identified in the three affected individuals reported here (c.899G>A; p.Arg300Gln; Matyas et al., 2014). The mutations at codon Arg300 presumably lead to increased TGF-beta signalling, suggesting that the short or tall stature seen in patients with TGFB3 mutations may result from opposing effects of mutations on TGF-beta signalling. Thus, we add a novel human TGFB3 mutation, contribute to the clinical delineation of the emerging connective tissue disorder tentatively called Rienhoff syndrome and compare the data with a very recent report (Bertoli-Avella et al., 2015) on TGFB3 mutations associated with aortic aneurysms or dissections.

Severe eczema and Hyper-IgE in Loeys-Dietz-syndrome - contribution to new findings of immune dysregulation in connective tissue disorders.

Loeys-Dietz syndrome (LDS) is a connective tissue disorder caused by monoallelic mutations in TGFBR1 and TGFBR2, which encode for subunits of the transforming growth factor beta (TGFß) receptor. Affected patients are identified by vascular aneurysms with tortuosity and distinct morphological presentations similar to Marfan syndrome; however, an additional predisposition towards asthma and allergy has recently been found. We describe two patients with a novel missense mutation in TGFBR1 presenting with highly elevated levels of IgE and severe eczema similar to autosomal-dominant Hyper-IgE syndrome (HIES). Mild allergic manifestations with normal up to moderately increased IgE were observed in 3 out of 6 additional LDS patients. A comparison of this cohort with 4 HIES patients illustrates the significant overlap of both syndromes including eczema and elevated IgE as well as skeletal and connective tissue manifestations.

Successful treatment of catecholaminergic polymorphic ventricular tachycardia with flecainide: a case report and review of the current literature.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease that can cause sudden cardiac death due to ventricular fibrillation (VF). While pharmacological therapy with beta-blockers and/or Ca(2)(+) antagonists is often unreliable, a recent study has demonstrated that flecainide can effectively suppress arrhythmia in a murine model of CPVT as well as clinically in two human subjects suffering from CPVT. We here present the case of an 11-year-old boy suffering from CPVT-1 as well as a review of the current relevant literature. After resuscitation due to VF at age 9, an automated implantable cardioverter-defibrillator (ICD) was implanted in 2007. Under beta-blocker therapy, repeated shocks were delivered due to either fast ventricular tachycardia (VT) or VF. This persisted under additional therapy with verapamil. Implantable cardioverter-defibrillator routine interrogations showed frequent non-sustained VT with an average of 8.8 per day. Additionally, the patient suffered from impaired physical performance due to decreased chronotropic competence. In July 2009, flecainide was added to the beta-blocker/verapamil regimen, resulting in a plasma level of 0.20 mg/L. No ICD shock or sustained VT occurred until December 2010. Genetic testing revealed an RyR2 receptor mutation. The case demonstrates the challenge of diagnosis and management of CPVT. It furthermore supports recent experimental evidence that the class 1 antiarrhythmic drug flecainide can suppress CPVT. The presented case supports a novel strategy in treating CPVT with the class I antiarrhythmic agent flecainide.

Late valvular and other cardiac diseases after different doses of mediastinal radiotherapy for Hodgkin disease in children and adolescents: report from the longitudinal GPOH follow-up project of the German-Austrian DAL-HD studies.

BACKGROUND: To analyze the impact of mediastinal irradiation on the incidence of cardiac late effects in long-term survivors of pediatric Hodgkin disease (HD). METHODS: The study cohort comprised 1,132 survivors of HD who received treatment before 18 years of age in consecutive trials between 1978 and 1995. They had maintained remission without secondary malignancy for 3.1-29.4 years. The cumulative doxorubicin dose was uniformly 160 mg/m(2), the mediastinal radiation dose (MedRD) was 36, 30, 25, 20, or 0 Gy. Follow-up questionnaires complemented by additional contacts served to collect information on late effects from patients and physicians. A central expert panel reviewed all reported cardiac abnormalities. RESULTS: By October 2008, cardiac diseases (CD) had been diagnosed in 50 of 1,132 patients aged 15.0-41.7 (median 32.2) years. The interval since HD therapy was 3.0-28.2 (median 19.5) years. Valvular defects were diagnosed most frequently, followed by coronary artery diseases, cardiomyopathies, conduction disorders, and pericardial abnormalities. The cumulative incidence of CD after 25 years was highest in the MedRD-36 group (21%) decreasing to 10%, 6%, 5%, and 3% in the lower MedRD groups (P < 0.001). Multivariate Cox analysis of several putative risk factors showed MedRD to be the only significant variable predicting for CD-free survival (P = 0.0025). CONCLUSIONS: Our results indicate that lower MedRDs are less cardiotoxic. Consequently, reduction of cardiac late effects may be expected with the lower radiation doses used in current HD protocols. Longer follow-up is needed to confirm the present results.

Late coil displacement after interventional closure of a perimembranous ventricular septal defect: a case report.

Muscular and perimembranous ventricular septal defects can be closed with nitinol plugs or spiral coils. Displacement and embolization of the device are well known complications that usually occur during or early after the procedure. We present the case of a 12-year-old boy with asymptomatic coil displacement detected at a routine examination 5 months after closure of a perimembranous ventricular septal defect.