There were no significant differences in the mRNA expression of NRTN, ARTN, PSPN, GFRA2, GFRA3, and GFRA4 between the AF and NP cells (relative expression (AF vs. NP): NRTN, 1.30 ± 1.13 vs. 0.65 ± 0.07; ARTN, 0.43 ± 0.79 vs. 0.11 ± 0.09; PSPN, 0.35 ± 0.37 vs. 0.98 ± 1.60; GFRA2, 0.18 ± 0.21 vs. 0.10 ± 0.11; GFRA3, 1.98 ± 2.54 vs. 1.03 ± 0.05; and GFRA4, 13.8 ± 14.6 vs. 2.11 ± 2.64). The gene discussed is GFRA4; the disease is atrial fibrillation.