PITX2 and ESR1 Expression in Craniofacial Asymmetry Subclassifications and TMD

Objectives: In previous studies, we found differences in gene expression of PITX2 between left and right masseter in adults with facial asymmetry. We also identified SNPs associating ESR1 as a risk factor for dysfunctional worsening of TMD after orthognathic surgery and ENPP1 as a protective factor against TMD in patients with dentofacial deformities. This study investigates how PITX2, ENPP1 and ESR1 gene expression associates given different prevalence of TMD in four subclassifications of facial asymmetry.

Methods: 174 orthognathic surgery subjects were diagnosed as symmetric or subdivided into four morphologically distinct asymmetric classifications as determined by PA cephalometric analysis. Jaw Pain and Function (JPF) questionnaires assessed presence and severity of TMD. Right and left masseter samples were collected during mandibular osteotomies. Total RNA was isolated to assay PITX2, ENPP1 and ESR1 quantities by TaqMan® RT-PCR. The difference in expression between facial sides and mean expression of facial sides were compared between symmetric controls and asymmetric subclassifications.
Results: Average JPF scores for asymmetric subjects (JPF=7) were significantly greater (p<0.001) than symmetric subjects (JPF=2). Asymmetric subclassifications showed significant differences (p=0.009), with Group-3 having the highest average score (JPF=9). Expression of PITX2 between left and right sides differed significantly (p<0.05) in asymmetry Group-3 compared to symmetry controls. Average expression of ESR1 differed significantly (p<0.02) in asymmetry Group-2 subjects compared to symmetric controls. Expression differences between right and left sides for ENPP1 and ESR1 and average expression of PITX2 and ENPP1 were not significant between groups.

Conclusions: PITX2 expression differs between left and right masseter muscles in asymmetry Group-3 and ESR1 had greater average expression in asymmetry Group-2. These findings suggest that both genes should be considered risk factors in development of craniofacial asymmetry and TMD.