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

Circ Res. 2017 May 12;120(10):e33-e44. doi: 10.1161/CIRCRESAHA.116.310112. Epub 2017 Feb 20.

Abstract

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 β2 subunit (Gβ2) 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 Gβ2 was coexpressed with Gγ2; this was in contrast to coexpression of mutant Gβ2-Gγ2 with other cardiac ion channels (HCN4, HCN2, and Cav1.2). Molecular dynamics simulations suggested a reduced binding property of mutant Gβ2 to cardiac GIRK channels when compared with native Gβ2.

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.

Keywords: atrial fibrillation; atrioventricular block; bradycardia; dizziness; sick sinus syndrome.

MeSH terms

  • Adult
  • Amino Acid Sequence
  • Atrioventricular Block / diagnosis
  • Atrioventricular Block / genetics*
  • Atrioventricular Block / physiopathology*
  • Female
  • GTP-Binding Proteins / genetics*
  • Gene Expression Profiling / methods
  • Genome-Wide Association Study / methods
  • HEK293 Cells
  • Heart Conduction System / physiopathology
  • Humans
  • Male
  • Middle Aged
  • Mutation / genetics*
  • Sick Sinus Syndrome / diagnosis
  • Sick Sinus Syndrome / genetics*
  • Sick Sinus Syndrome / physiopathology*
  • Sinoatrial Node / physiology
  • Young Adult

Substances

  • GNB2 protein, human
  • GTP-Binding Proteins