# The Heritability of Upper Airway Dimensions Using MRI Scans in Twins
## 3 Results
### ACE Model  
The ACE statistical model of the measurements is summarized in Table 2, with the best fitting sub-model for each parameter. We found a strong heritable component determining subcutan fat-tissue thickness of the neck and tongue anteroposterior diameter. On the other hand, we found a strong environmental contribution to the parapharyngeal adipose tissue area and the pharyngeal wall thickness. The PAS diameter was determined mostly by _heritable_ factors in the nasal region; however, the occlusal thickness of the PAS, which is the narrowest point of the upper airway, was mainly affected by environmental factors. The PAS area had to be eliminated due to distributional problems. The SNA and SNB angles showed both genetic and environmental contributions, with a slightly larger _heritable_ impact regarding the SNB angle. Most parameters of the uvula were also both affected by _hereditary_ and environmental factors except for the area that showed a higher environmental determination. To better visualize the ACE differences between the traits, we demonstrate the distribution of each model from the highest A values to the highest E values in Figure 7.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Total** & **MZ** & **DZ** & \(p\)**-Values** \\ \hline Number of participants, N & 110 & 66 & 44 & \\ \hline Age, (years) median (Q1–Q3) & 53 (44–64) & 50 (42–56) & 59 (48–69) & 0.002 \\ \hline \multirow{4}{*}{Sex, N (\%)} & Males: 34 & Males: 24 & Males: 10 & \\  & (30.9) & (36.4) & (22.7) & \\ \cline{1-1}  & Females: 76 & Females: 42 & Females: 34 & \\ \cline{1-1}  & (69.1) & (63.6) & (77.3) & \\ \hline BMI, median (Q1–Q3) & 24.8 & 24.3 & 25.2 & \\ \cline{1-1}  & (22.4–27.3) & (22.2–27.2) & (23.1–27.7) & 0.803 \\ \hline Smoking, N (\%) & 16 (14.5) & 13 (19.7) & 3 (6.8) & 0.096 \\ \hline Hypertension, N (\%) & 24 (21.8) & 12 (18.2) & 12 (27.3) & 0.346 \\ \hline Diabetes Mellitus, N (\%) & 7 (6.4) & 3 (4.5) & 4 (9.1) & 0.434 \\ \hline Dyslipidemia, N (\%) & 20 (18.2) & 9 (13.6) & 11 (25) & 0.140 \\ \hline BMI, body mass index & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Demographics and descriptive clinical characteristics of the study subjects. The continuous variables are expressed as the median (Q1–Q3) deviation. \(p\)-values of the Fisher’ exact test and the Mann–Whitney U tests for each parameter are shown.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Measurements** & **A** & **C** & **E** \\ \hline SNA angle & A: 0.485 (0.142, 0.713) & C: 0 & E: 0.515 (0.287, 0.858) \\ \hline SNB angle & A: 0.702 (0.422, 0.849) & C: 0 & E: 0.298 (0.151, 0.578) \\ \hline Mandibular–hyoid distance & A: 0 & C: 0.569 (0.312, 0.746) & E: 0.431 (0.254, 0.688) \\ \hline Hyoid–cervical tangent distance & A: 0 & C: 0.685 (0.510, 0.805) & E: 0.315 (0.195, 0.490) \\ \hline Soft palate length & A: 0 & C: 0.629 (0.437, 0.765) & E: 0.371 (0.235, 0.563) \\ \hline Soft palate thickness & A: 0.666 (0.442, 0.804) & C: 0 & E: 0.334 (0.196, 0.558) \\ \hline Soft palate area & A: 0 & C: 0.633 (0.444, 0.768) & E: 0.367 (0.232, 0.556) \\ \hline Uvula sagittal thickness & A: 0.707 (0.507, 0.829) & C: 0 & E: 0.293 (0.171, 0.493) \\ \hline Uvula axial anteroposterior width & A: 0.651 (0.308, 0.827) & C: 0 & E: 0.349 (0.173, 0.692) \\ \hline Uvula axial width & A: 0.732 (0.469, 0.863) & C: 0 & E: 0.268 (0.137, 0.531) \\ \hline \hline \end{tabular}
\end{table}
Table 2: ACE models of the measured anatomical markers with 95% confidence interval after defining the best fitting sub-model. A: additive genetics, C: common environment, E: unique environment.