Identification of a KCNE2 Gain-of-Function Mutation in Patients with Familial Atrial Fibrillation

Abstract

Atrial fibrillation (AF) is the most common cardiac arrhythmia encountered in clinical practice. We first reported an S140G mutation of KCNQ1, an alpha subunit of potassium channels, in one Chinese kindred with AF. However, the molecular defects and cellular mechanisms in most patients with AF remain to be identified. We evaluated 28 unrelated Chinese kindreds with AF and sequenced eight genes of potassium channels (KCNQ1, HERG, KCNE1, KCNE2, KCNE3, KCNE4, KCNE5, and KCNJ2). An arginine-to-cysteine mutation at position 27 (R27C) of KCNE2, the beta subunit of the KCNQ1-KCNE2 channel responsible for a background potassium current, was found in 2 of the 28 probands. The mutation was present in all affected members in the two kindreds and was absent in 462 healthy unrelated Chinese subjects. Similar to KCNQ1 S140G, the mutation had a gain-of-function effect on the KCNQ1-KCNE2 channel; unlike long QT syndrome-associated KCNE2 mutations, it did not alter HERG-KCNE2 current. The mutation did not alter the functions of the HCN channel family either. Thus, KCNE2 R27C is a gain-of-function mutation associated with the initiation and/or maintenance of AF.

Novel KCNA5 loss-of-function mutations responsible for atrial fibrillation

“…In the other 11 investigated genes, no more mutations were identified in the 120 probands, except those that were reported earlier. 12,17,21 Multiple alignment of the Kv1.5 protein sequences across species A cross-species alignment of Kv1.5 protein sequences showed that the altered amino acids, except for Ala576, are completely conserved evolutionarily (Figure 3). in the net outward current compared with that generated by the expression of wild-type KCNA5 alone (Figure 4).…”

“…Specific variations in several genes associated with AF were identified and characterized. These AF-related genes are mainly as follows: KCNQ1, which encodes the a-subunit of slowly activating delayed rectifier potassium channel (IKs); 12 HERG, which encodes the a-subunit of the rapidly activating delayed rectifier potassium channel (IKr); 13 SCN5A, which encodes the a-subunit of the sodium channel; 14,15 Ankyrin-B, which encodes a member of a family of versatile membrane adapters, which is required for coordinated assembly of the Na/Ca exchanger, Na/K ATPase and inositol trisphosphate receptor at transverse tubule/sarcoplasmic reticulum sites in cardiomyocytes; 16 KCNJ2, which encodes the a-subunit of inward rectifier potassium channel (IK1); 17 KCNA5, which encodes the a-subunit of the ultrarapidly activating delayed rectifier potassium channel (Kv1.5); 18 Connexin 40, which is expressed selectively in atrial myocytes and mediates the coordinated electrical activation of the atria; 19 KCNE1, which encodes the b-subunit of IKs; 20 KCNE2 encoding b-subunit of IKr; 21 and KCNE3, 22 KCNE4 23 and KCNE5, 24 which encode the b-subunits of potassium channels interacting with KCNQ1, HERG and others. In addition, inheritable defects also confer substantial disease susceptibility on patients with secondary AF.…”

Genetic Discoveries in Atrial Fibrillation and Implications for Clinical Practice

“…Both gain-of-function and loss-of-function mutations in genes encoding potassium and sodium channel subunits have been reported to underlie familial AF. [2][3][4][5][6][7][8][9][11][12][13]25,26,[29][30][31]43 Gain-offunction potassium channel mutations are predicted to influence AF by shortening the atrial effective refractory period, an effect that would be predicted to promote atrial re-entry. 44 Loss-of-function potassium channel mutations are predicted to promote triggered activity in the atrium, which is also an important contributor to the genesis of AF.…”

Differentiation of Human Atrial Myocytes From Endothelial Progenitor Cell-Derived Induced Pluripotent Stem Cells

“…In recent years, familial forms of atrial fibrillation have been explored using sophisticated molecular approaches. One such study demonstrated a causative role mutation in the potassium channels responsible for the slow re-polarization of atrial myocytes (KCNQ1, KCNE2, KCNJ2) [320][321][322]. However, the vast majority of atrial fibrillation is sporadic and non-familial.…”