ADRB2 and Schnyder corneal dystrophy: For example, epinephrine, a neurotransmitter in pain signaling, has been shown to target the beta-2 adrenergic receptor (ADRB2) and polymorphisms in the ADRB2 gene have been linked to chronic and acute pain in SCD, along with other conditions such as functional gastrointestinal and temporomandibular disorders (28, 35, 41, 42).