COMT and irritable bowel syndrome: Further supporting the role of catecholamine signaling in determining IBS symptom severity, SNP ADRA1D or Alpha-1A adrenergic receptor (ADRA1A) [28] rs1556832 has been proposed as having interactions with COMT and alpha-adrenergic-β2 (ADRAβ2) to worsen the severity of IBS gastrointestinal symptoms [24].