Genome-wide association reveals contribution of MRAS to painful temporomandibular disorder in males.

Painful temporomandibular disorders (TMD) is the leading cause of chronic orofacial pain, but its underlying molecular mechanisms remain obscure. While many environmental factors have been associated with higher risk of developing painful TMD, family and twin studies support a heritable genetic component as well. We performed a GWAS assuming an additive genetic model of TMD in a discovery cohort of 999 cases and 2031 TMD-free controls from the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study. Using logistic models adjusted for sex, age, enrollment site, and race, we identified three distinct loci that were significant in combined or sex-segregated analyses. A single nucleotide polymorphism (SNP) on chromosome 3 (rs13078961) was significantly associated with TMD in males only (odds ratio [OR]=2.9, 95% CI: 2.02-4.27, P=2.2x10). This association was nominally replicated in a meta-analysis of seven independent orofacial pain cohorts including 160,194 participants (OR=1.16, 95% CI: 1.0-1.35, P = 2.3x10). Functional analysis in human dorsal root ganglia (DRG) and blood indicated this variant is an expression quantitative trait locus (eQTL), with the minor allele associated with decreased expression of the nearby muscle RAS oncogene homolog (MRAS) gene (beta = -0.51, P = 2.43x10). Male mice, but not female mice, with a null mutation of Mras displayed persistent mechanical allodynia in a model of inflammatory pain. Genetic and behavioral evidence support a novel mechanism by which genetically-determined MRAS expression moderates the resiliency to chronic pain. This effect is male-specific and may contribute to the lower rates of painful TMD in men.Written work prepared by employees of the Federal Government as part of their official duties is, under the U.S. Copyright Act, a "work of the United States Government" for which copyright protection under Title 17 of the United States Code is not available. As such, copyright does not extend to the contributions of employees of the Federal Government.