Cellular pathway analysis from a human genetic association study identified a serotonergic receptor 2 pathway that contributed to localized manifestations of facial pain.
Human association studies of common genetic polymorphisms have identified many loci that are associated with risk of complex diseases, although individual loci typically have small effects. However, by envisaging genetic associations in terms of cellular pathways, rather than any specific polymorphism, combined effects of many biologically relevant alleles can be detected. The effects are likely to be most apparent in investigations of phenotypically homogenous subtypes of complex diseases. We report findings from a case-control, genetic association study of relationships between 2925 single nucleotide polymorphisms (SNPs) and 2 subtypes of a commonly occurring chronic facial pain condition, temporomandibular disorder (TMD): 1) localized TMD and 2) TMD with widespread pain. When compared to healthy controls, cases with localized TMD differed in allelic frequency of SNPs that mapped to a serotonergic receptor pathway (P = 0.0012), while cases of TMD with widespread pain differed in allelic frequency of SNPs that mapped to a T-cell receptor pathway (P = 0.0014). A risk index representing combined effects of 6 SNPs from the serotonergic pathway was associated with greater odds of localized TMD (odds ratio 2.7, P = 1.3 E-09), and the result was reproduced in a replication case-control cohort study of 639 people (odds ratio 1.6, P = 0.014). A risk index representing combined effects of 8 SNPs from the T-cell receptor pathway was associated with greater odds of TMD with widespread pain (P = 1.9 E-08), although the result was not significant in the replication cohort. These findings illustrate potential for clinical classification of chronic pain based on distinct molecular profiles and genetic background.
aRegional Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
bDepartment of Dental Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
cDepartment of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
dNational Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
eAriadne Diagnostics LLC, Rockville, MD, USA
fDepartment of Community Dentistry & Behavioral Science, University of Florida, Gainesville, FL, USA
gDepartment of Oral Diagnostic Sciences, University at Buffalo, Buffalo, NY, USA
hUniversity of Maryland School of Dentistry, Baltimore, MD, USA
*Corresponding authors. Address: Regional Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. Tel.: +1 919 537 3273; fax: +1 919 966 5339.
Submitted November 1, 2012; revised June 24, 2013; accepted July 9, 2013.