Similar to propranolol, butoxamine increased paw withdrawal threshold in SMA mice in a dose-dependent manner, whereas atenolol and SR 59230 A had no effects (Fig. 6c–e), indicating that the β2 adrenergic receptor (ADRB2) mediates adrenergic signaling involved in SMA-associated pain hypersensitivity. The gene discussed is ADRB2; the disease is proximal spinal muscular atrophy.