Although evidence shows that several dopamine neurotransmission pathway genes are associated with specific clinical pain syndromes, such as fibromyalgia, chronic headache, and postoperative pain, the exact role of dopamine in pain processing is not fully understood. [Note: Dopamine is a brain chemical responsible for stimulation and feelings of enjoyment. Some leading researchers believe dopamine dysregulation plays a key role in fibromyalgia - see "An Elephant Among Us: The Role of Dopamine in the Pathophysiology of Fibromyalgia."]
The aim of this study was to explore the relationship between functional polymorphisms [variants] in dopaminergic candidate genes and sensitivity to pain in healthy subjects.
Healthy subjects (n=192; 105 F, 87 M) were exposed to experimental tonic cold pain (1 degrees C) and phasic heat pain (47 degrees C) stimuli. DNA samples were obtained from both participants and their parents. The relationships between pain response (intensity in response to heat and cold; threshold and tolerance in response to cold only) and the functional Variable Number of Tandem Repeat (VNTR) polymorphisms of three dopamine-related genes were investigated using a Transmission Disequilibrium Test (TDT). Specifically, 30-bp repeat in the promoter region of the monoamine oxidase-A gene (MAO-A), 40-bp repeat in the 3'-untranslated region of the dopamine transporter gene (DAT-1), and 48-bp repeat in the exon 3 of the dopamine receptor 4 gene (DRD4) were examined.
Significant associations between cold pain tolerance and DAT-1 (p=0.008) and MAO-A (p=0.024) polymorphisms were found.
Specifically, tolerance was shorter for carriers of allele 10 and the rarer allele 11, as compared to homozygous for allele 9, and for carriers of allele 4 as compared to homozygous for allele 3, respectively.
These results, together with the known function of the investigated candidate gene polymorphisms, suggest that low dopaminergic activity can be associated with high pain sensitivity and vice versa.
Source: Pain, Sep 29, 2009. PMID: 19796878, by Treister R, Pud D, Ebstein RP, Laiba E, Gershon E, Haddad M, Eisenberg E. The Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel; Pain Research Group, Haifa; Faculty of Social Welfare and Health Sciences, University of Haifa; S. Herzog Memorial Hospital, Jerusalem; Pain Relief Unit, Rambam Medical Center, Haifa, Israel. [E-mail: email@example.com]