## 4 Discussion  
In the current study on discordant twins, we demonstrated that accumulated parapharyngeal fat tissue, independently of genetic background and common environmental factors, is associated with elevated body weight and waist circumference and higher metabolism which may further prove the role of central type obesity and upper airway narrowing. Higherumental fat tissue thickness was also associated with lower muscle percentage. We also found an interesting correlation between anatomic markers and decreased IMT values. The narrowest width of the posterior airway space showed a correlation with IMT and EMT thickness as well as elevated BMI values. To our knowledge, this is the first study on discordant monozygotic twins investigating the background of anatomic markers associated with upper airway narrowing. Obesity is evidently a highly heritable condition which further leads to a higher genetic determination of upper airway narrowing and possible OSA development itself. The accumulation of parapharyngeal fat tissue induces the narrowing of the upper airways in obese subjects. During a weight reduction program, a decrease in parapharyngeal fatty \begin{table}
\begin{tabular}{c c c c} \hline
**Discordant Parameter** & **Investigated Parameter** & **Mean Difference** & \(p\)**Value** \\ \hline \multirow{3}{*}{Submental neck fat thickness} & Muscle percentage (\%) & \(-1.067\) & \(<\)0.05 \\  & Right CCA mean CIMT (mm) & \(-0.066\) & \(<\)0.05 \\ \hline \multirow{4}{*}{Parapharyngeal fat area} & Weight (kg) & 5.986 & \(<\)0.05 \\  & Waist circumference (cm) & 6.589 & \(<\)0.05 \\  & Metabolism (kcal) & 91.244 & \(<\)0.05 \\  & Left CCA mean CIMT (mm) & \(-0.008\) & \(<\)0.05 \\  & Right CCA mean CIMT (mm) & \(-0.067\) & \(<\)0.05 \\  & Right CFA mean IMT (mm) & \(-0.026\) & \(<\)0.05 \\ \hline \multirow{2}{*}{Tongue volume} & Left ICA mean CIMT (mm) & \(-0.012\) & \(<\)0.01 \\  & Left CFA mean IMT (mm) & \(-0.044\) & \(<\)0.05 \\ \hline \multirow{4}{*}{Posterior airway space occlusal width} & Left ICA mean CIMT (mm) & \(-0.059\) & \(<\)0.05 \\  & Left CFA mean IMT (mm) & \(-0.035\) & \(<\)0.05 \\ \cline{1-1}  & Left CCA EMT (mm) & \(-0.12\) & \(<\)0.05 \\ \cline{1-1}  & BMI (kg/m\({}^{2}\)) & \(-0.764\) & \(<\)0.05 \\ \hline \end{tabular}
\begin{tabular}{c c c} \hline
**IMT: intima-media thickness, CIMT: carotid intima-media thickness, CCA: common carotid artery, ICA: internal carotid artery, CFA: common femoral artery, EMT: extra-medial thickness, BMI: body-mass index.** \\ \end{tabular}
\end{table} 
Table 4: Significant associations between discordant anatomic parameters and individual parameters determined by paired permutation tests. \begin{table}
\begin{tabular}{c c c} \hline
**Measured Parameter** & **Number of Discordant Pairs** & **Significant Association (\(p<0.05\))** \\ \hline \multirow{4}{*}{Tongue thickness} & \multirow{2}{*}{2} & none \\  & Tongue volume & 10 & \(-\): mean IMT left ICA and CFA \\ \cline{1-1}  & & Left: 11, Right: 9 & none \\ \cline{1-1}  & & & \\ \cline{1-1}  & & Left: 5, Right: 2 & none \\ \cline{1-1}  & & & \\ \cline{1-1  
tissue and improved OSA symptoms were reported [21]. Our study results suggested that patients with higher BMI had significantly narrower posterior airway space which further proves the effect of obesity on upper airway obstruction. BMI is a widely accepted rough screening method of body weight categorization; however, it does not take into consideration excess weight caused by increased muscularity and also does not provide information regarding obesity types. Whole body composition analysis scales, however, combined with hip and waist circumference registration give more detailed insight into the composition of the body thus providing additional information on overweight subjects' risk for OSA. Central-type obese patients have a higher risk of developing diseases associated with obesity compared to peripheral obesity [22]. The body type of the patient could easily be determined by the waist-to-hip ratio.