- Chromosome 4q25 variants are genetic modifiers of rare ion channel mutations associated with familial atrial fibrillation. Marylyn D. Ritchie, Shane Rowan, Gayle Kucera, Tanya Stubblefield, Marcia Blair, Shannon Carter, Dan M. Roden, Dawood Darbar, Copyright (c) 2012 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved., 60, 13, 1173-1181, of the American College of Cardiology, 2012 Sep 25, PMID: 22818067 PMCID: PMC3448817,