Both types contain C-terminal FH1 and FH2 domains, which are evolutionarily conserved [23,24]: the FH1 domain promotes AF elongation by binding to profilin–actin monomers via its polyproline domains [25,26], while the FH2 domain is essential for AF nucleation [3,27]. The gene discussed is FLNB; the disease is atrial fibrillation.