Among the pattern of autoantibodies to β1-AR isolated from the blood of patients with dilated cardiomyopathy, antibodies designated as “P4” predominate, which suppress the internalization of receptors, cause a β1-AR-mediated increase in intracellular cAMP levels in the absence of an agonist, and inhibit the stimulating effect of isoproterenol on AC activity [439]. The gene discussed is ADRB1; the disease is dilated cardiomyopathy.