Table 4.

Genes encoding the neurotransmitter systems and their role in pain.

Encoding gene	Nature of pain	Site
GCH1 (gene encoding cyclohydrolase 1)	Decreased risk	Experimental and post-discectomy pain Decreased pain reporting and decreased specialized pain therapy following diagnosis of cancer
SLC6A4 (serotonin transporter gene)	Increased risk	Chronic widespread pain and emotional modulation of pain
ADRB2 (gene coding for β 2 adrenergic receptor)	Increased risk	Chronic widespread pain and self-reporting for the extent and duration of pain.
HTR2A (gene coding for serotonin receptor 2A)	Increased risk	Chronic widespread pain and post-surgical pain