ADRB2 and postural orthostatic tachycardia syndrome: Hall et al, in their study with 116 POTS patients and 81 controls, documented that autoantibody concentrations (AT1R, ETAR (endothelin type A receptor), ADRA1, ADRA2, ADRB1, ADRB2, and M1R through M5R) were not different in POTS patients and healthy controls.