SCN1Bb R214Q found in 3 patients: 1 with Brugada syndrome and 2 with lone atrial fibrillation

BACKGROUND: SCN1Bb encodes the β-subunit of the sodium channel. A mutation in SCN1Bb R214Q has recently been shown both to increase the Kv4.3 current and to decrease the sodium current. The variant was suggested to increase the susceptibility to Brugada syndrome (BrS). OBJECTIVE: To sequence a population of BrS and early-onset lone atrial fibrillation (AF) patients for the R214Q mutation in the SCN1Bb gene. METHODS: The coding sequence and splice junctions of SCN1Bb were bidirectionally sequenced by using Big Dye chemistry in 192 early-onset lone AF patients and 22 BrS patients. RESULTS: Three probands carrying the R214QC variant were identified. No mutations were identified in genes previously associated with BrS or AF in these patients. Case 1 was a BrS patient with a type 1 electrocardiogram and onset of disease at the age of 54 years. Case 2 was a lone AF case with onset at the age of 39 years and paroxysmal lone AF. Case 3 also had the onset of persistent lone AF at the age of 39 years. Both lone AF patients had electrocardiograms that raised the suspicion of BrS, but intravenous flecainide testing was, in both cases, negative. R214Q was not present in the control group (n = 216) and has not previously been reported in conjunction to AF. CONCLUSION: Three patients of 192 young lone AF and 22 BrS patients carried the nonsynonymous R214Q mutations in SCN1Bb, thereby indicating that this variant increases the susceptibility to both BrS and AF.