Atrial Fibrillation via the GJA5 Gene

Atrial fibrillation is a disorder with an abnormal and often rapid heart rhythm. This condition is characterized by uncoordinated electrical activity in the atria, “irregularly irregular” pattern in ECG and supraventricular tachyarrhythmia, which deteriorates atrial mechanical function. If untreated, atrial fibrillation can lead to a reduction in cardiac output, atrial thrombus formation and increased risk for mortality. Patients with atrial fibrillation can present dizziness, chest pain, palpitations, shortness of breath, or even syncope (Fuster et al. 2011). Complications of atrial fibrillation can occur at any age and some people may never experience any health problems. The likelihood of developing arrhythmias increases with age. Atrial fibrillation can be prevented and treated (Van Wagoner et al. 2015).

Atrial fibrillation (AF) is the most common cardiac arrhythmia disorder, and currently affects nearly 3 million Americans (Naccarelli et al. 2009). Although the incidence of the familial form of atrial fibrillation is unknown, having a family member with AF is associated with a 40% increased risk for atrial fibrillation (Lubitz et al. 2010).

Familial atrial fibrillation is a highly heterogeneous disease and is transmitted in an autosomal dominant pattern. There are at least 15 genes associated with familial atrial fibrillation: ABCC9, GJA5, KCNA5, KCND3, KCNE1, KCNE1L, KCNE2, KCNH2, KCNJ2, KCNQ1, NPPA, SCN1B, SCN2B, SCN3B and SCN5A. The majority of genes associated with atrial fibrillation are components of two important ion channels: potassium and sodium. Both loss and gain of function variants in those genes can affect the current of ion channel and change the atrial action potential and refraction period (Tucker et al. 2014). A few non-ion channel genes instigate the atrial fibrillation by an alternative mechanism. GJA5 is one of them.

GJA5 encodes the gap junction protein, Connexin 40. Gap junctions are a specialized intercellular connection and provide direct intercellular communication. In the heart, gap junctions mediate electrical coupling between cells. Variants in GJA5 could disrupt the propagation of action potential between cardiomyocytes (Gollob et al. 2006).

Clinical sensitivity is not available because only a limited number of patients have been reported (Olesen et al. 2014; Lübkemeier et al. 2013). Gross deletions or duplications not detectable by Sanger sequencing have been reported in GJA5 as individual cases of Tetrology of Fallot, but no statistics are yet available (Human Gene Mutation Database).

This test provides full coverage of all coding exons of the GJA5 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).