# The Heritability of Upper Airway Dimensions Using MRI Scans in Twins
## 4 Discussion  
The present study investigated the heritability of the anatomical markers of OSA on MRI scans. Our main results showed that in our study population, the anteroposterior diameter of the tongue and the neck subcutaneous fat tissue were strongly determined by hereditary influences. The pharyngeal wall thickness and parapharyngeal fat tissue areas were mainly determined by environmental factors. The collapse of the upper airways during OSA can occur at numerous levels of the nose, nasopharyngeal, oropharynx, epiglottis, or hypopharynx [38]. There have been several studies investigating the relationship between anatomic features and OSA. Facial skeleton abnormalities of the maxilla and mandibula have been associated with the development of OSA. These bony structure malformations could lead to soft tissue redistribution and pharyngeal airway space reduction [39; 40; 41]. An inferior and posterior replacement of the hyoid bone has been detected in OSA patients, which could be explained by the mobility of the bone and the caudal expansion of the soft tissue. This leads to instability and the posterior replacement of the tongue, causing airway narrowing [42; 43; 41]. We found a similar hereditary and environmental determination of the cephalometric parameters. Anatomical abnormalities of the surrounding soft tissues such as lateral pharyngeal walls, tonsils, and tongue are also associated with an increased risk for OSA [44]. Based on \begin{table}
\begin{tabular}{c c c} \hline
**Measurements** & **RMZ** & **RDZ** \\ \hline SNA angle & 0.511 (0.120, 0.764) & 0.297 (\(-\)0.267, 0.710) \\ \hline SNB angle & 0.716 (0.445, 0.866) & 0.129 (\(-\)0.433, 0.616) \\ \hline Mandibular–hyoid distance & 0.538 (0.156, 0.782) & 0.623 (0.181, 0.856) \\ \hline Hyoid–corvical tangent distance & 0.550 (0.236, 0.760) & 0.811 (0.595, 0.918) \\ \hline Soft palate length & 0.724 (0.504 0.854) & 0.429 (0.017, 0.715) \\ \hline Soft palate thickness & 0.640 (0.376, 0.809) & 0.465 (0.060, 0.740) \\ \hline Soft palate area & 0.673 (0.431, 0.825) & 0.614 (0.271, 0.819) \\ \hline Uvula sagittal thickness & 0.707 (0.484, 0.843) & 0.412 (0.01, 0.699) \\ \hline Uvula axial anteroposterior width & 0.568 (0.179, 0.799) & 0.428 (\(-\)0.186, 0.781) \\ \hline Uvula axial width & 0.612 (0.270, 0.815) & 0.521 (0.018, 0.811) \\ \hline Uvula area & 0.602 (0.263, 0.81) & 0.577 (0.078, 0.843) \\ \hline PAS nasal & 0.489 (0.181, 0.709) & 0.283 (\(-\)0.145, 0.620) \\ \hline PAS occlusal & 0.595 (0.313, 0.782) & 0.569 (0.196, 0.8000) \\ \hline Tongue anteroposterior diameter & 0.856 (0.694, 0.934) & 0.079 (\(-\)0.416, 0.536) \\ \hline Tongue thickness & 0.793 (0.563, 0.905) & 0.446 (\(-\)0.120, 0.782) \\ \hline Tongue axial width & 0.639 (0.315, 0.825) & 0.515 (\(-\)0.055, 0.818) \\ \hline Tongue volume & 0.666 (0.36 0.84) & 0.525 (\(-\)0.008, 0.815) \\ \hline Tongue area & 0.588 (0.282, 0.761) & 0.45 (\(-\)0.015, 0.721) \\ \hline Subcutaneous neck fat thickness & 0.834 (0.681, 0.917) & 0.598 (0.238, 0.815) \\ \hline Parapharyngeal fat area (right) & 0.603 (0.269, 0.805) & 0.624 (0.174, 0.853) \\ \hline Parapharyngeal fat area (left) & 0.656 (0.343, 0.836) & 0.597 (0.101, 0.846) \\ \hline Pharyngeal wall-parapharyngeal fat (right) & 0.510 (0.128, 0.757) & 0.616 (0.168, 0.85) \\ \hline Pharyngeal wall-parapharyngeal fat (left) & 0.510 (0.135, 0.756) & 0.561 (0.099, 0.823) \\ \hline Pharyngeal wall-internal carotid artery (right) & 0.493 (0.115, 0.746) & 0.568 (0.102, 0.827) \\ \hline Pharyngeal wall-internal carotid artery (left) & 0.493 (0.120, 0.744) & 0.518 (0.036, 0.802) \\ \hline \end{tabular} SNA, sella-nasion-A point (subspinal), SNB, sella-nasion-B point (supramental), PAS, posterior airway space.  
\end{table} 
Table 3: Intraclass correlations of MZ and DZ groups RMZ: MZ correlation, RDZ: DZ correlation. our results, the pharyngeal wall thickness was mainly affected by environmental factors. Similarly to us, [PERSON] et al.