The Many Faces of the Genetics

Oakley M, Vieira AR: The many faces of the genetics contribution to temporomandibular joint disorder Orthod Craniofac Res 2008;11:125–135.

M. Oakley, Department of Restorative Dentistry ⁄ Comprehensive Care, School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA, USA, A.R. Vieira, Departments of Oral Biology and Pediatric Dentistry and Center for Dental and Craniofacial Genetics, School of Dental Medicine, and Department of Human Genetics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA.

Abstract
Chronic pain disorders are estimated to cost approximately $80 billion per year in health care costs and lost productivity in the United
States (1, 2).
 
Pain in the facial region, including orofacial pain and craniofacial pain (excluding the traditional headache), accounts fora significant proportion of the approximately 10% of the Americans that suffer from chronic pain conditions. Sources of orofacial pain include caries, periodontal diseases, and neuropathic and musculoskeletal conditions (8). Orofacial pain is a major symptom of temporomandibular joint disorders (TMD) (9) and among the orofacial pain disorders, TMD comprise a relevant proportion of the total cases. The current treatments for these conditions could benefit from new approaches (10, 11) however, persistent pain among patients constitutes a public health concern that inflicts especially women between 20 and 40 years of age (2, 11–18). Studies concerning TMD have been limited because of the heterogeneous nature of symptoms leading to difficulties in diagnosis (19–21).

As reported by the National Institute of Dental Craniofacial Research (NIDCR) of the National Institutes of Health (NIH), TMD is known to affect over 10 million people in the USA at any given time. This disorder afflicts both men and women, however, women in their childbearing years constitute approximately 90% of those seeking treatment.

Objectives – Review the literature on candidate genes for temporomandibular joint disorder (TMD).

Setting and Sample Population – Literature review.

Materials and Methods – Two basic approaches were used to obtain literature in any language regarding genes and TMD. First, Medline, Embase, and Science Citation Index databases were searched using the keywords temporomandibular joint disorder and temporomandibular joint dysfunction for studies published from 1966 to 2007. Then, the references list of the studies obtained in the database was also considered.

Results – Candidate genes for TMD include genes for individual variations in pain perception, gender and ethnicity, proinflammatory cytokines, female hormones, breakdown of extracellular matrix, and syndromic forms of TMD.

Conclusion – Most of the studies on genetic variation contributing to TMD are approaching the disease mainly from an immune-inflammatory perspective. Recent investigations of the genetic variables which may predict identifiable levels of pain perception may uncover new approaches to our traditional treatment modalities for the chronic pain patient.

Temporomandibular joint disorder is a collection of symptoms related to the muscles and joints of the masticatory system. They likely comprise a number of etiologically distinct conditions that lead to similar symptoms. As individuals are not equally susceptible to TMD, this condition appears to be the result of the person s unique genetic makeup. For that reason, it has been suggested that a better understanding of the genetics modulating TMD is a necessary step that will lead to innovative therapies related to these conditions.