Heritability of cephalometric variables of airway morphology in twins with completed active growth

BackgroundThe interplay between genetic and environmental impacts on dental and facial morphology has been widely analyzed, but little is known about their relative contributions to airway morphology. The aim of this study was to evaluate the genetic and environmental influences on the cephalometric variables of airway morphology in a group of postpubertal twins with completed craniofacial growth.Materials and methodsThe materials comprised lateral head cephalograms of 94 pairs of twins (50 monozygotic, 44 dizygotic) with completed craniofacial growth. Zygosity was determined using 15 specific DNA markers. The computerized cephalometric analysis included 22 craniofacial, hyoideal, pharyngeal structural linear and angular variables. Genetic analysis and heritability estimation were performed using maximum likelihood genetic structural equation modeling (GSEM). Principal component analysis (PCA) was used to assess the correlations between cephalometric measurement variables.ResultsUpper airway dimensions showed moderate to high genetic determination (SPPW-SPP and U-MPW: a(2) = 0.64 and 0.5, respectively). Lower airway parameters showed only common and specific environmental determination (PPW-TPP a(2) = 0.24, e(2) = 0.38; LPW-V c(2) = 0.2, e(2) = 0.63; PCV-AH c(2) = 0.47, e(2) = 0.28). The relationship between the maxilla and the hyoid bone (for variables PNS-AH, ANS-AH d(2) = 0.9, 0.92, respectively) showed very strong additive genetic determination. The size of the soft palate was affected by additive and dominant genes. Its length (SPL) was strongly influenced by dominant genes, while its width (SPW) showed a moderate additive genetic influence. Owing to correlations in the behavior of variables, the data could be expressed in 5 principal components that jointly explained 36.8% of the total variance.ConclusionsThe dimensions of the upper airway are strongly determined by genes, while the parameters of the lower airway depend mainly on environmental factors.