ADRB2 and Aganglionic megacolon: Indeed, others have reported a predominance of β1-adrenergic receptor (AR) and muscarinergic 2 (M2) receptor autoantibodies in Chagas cardiomyopathy patients and of β2-AR with M2 autoantibodies in megacolon patients, and have suggested their utility for risk assessment of clinical disease [49].