## 2 Results
### Characterization of IDRs within IDLs in the NaV1.5 Channel  
To characterize IDL domains in the NaV1.5 channel, we compared cryoEM data of the NaV1.5 protein with the in silico prediction of disordered protein regions using three programs: PONDR-VLXT, PONDR-VSL2B, and PONDR-VL3 (Figure 1B,C). This analysis predicted 25 putative IDRs, including four fragments with more than 30 amino acids that have a consistent pattern across all members of the NaV channel family (amino acid positions IDR1 20-66, IDR2 441-532, IDR3 993-1111, 1125-1162, and IDR4 1932-1980) (Supplementary Figures S1 and S2), and phased in the IDL domains. The family of voltage-gated sodium channels includes nine members (NaV1.1-NaV1.9), with NaV1.5 being the longest. We calculated the disorder propensity degree for each family member and found that NaV1.5 had the highest average prediction score (0.328), the highest number of disordered amino acids (637), and the highest percentage of IDRs in the total protein length (31.6%) (Table 2). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Protein**} & **Length** & \multirow{2}{*}{**N.of IDR**} & **Average** & **N.of Disordered** & **Percentage** \\  & **(AA)** & & **Prediction Score** & **AA** & **of IDR** \\ \hline
**NaV1.1** & 2009 & 29 & 0.275 & 517 & 25.73 \\
**NaV1.2** & 2005 & 25 & 0.276 & 538 & 26.83 \\
**NaV1.3** & 2000 & 23 & 0.268 & 520 & 26 \\
**NaV1.4** & 1836 & 19 & 0.253 & 437 & 23.80 \\
**NaV1.5** & 2016 & 25 & 0.328 & 637 & 31.60 \\
**NaV1.6** & 1980 & 24 & 0.268 & 504 & 25.45 \\
**NaV1.7** & 1988 & 29 & 0.282 & 538 & 27.08 \\
**NaV1.8** & 1956 & 25 & 0.272 & 498 & 25.46 \\
**NaV1.9** & 1791 & 21 & 0.219 & 330 & 18.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: IDR enrichment in the voltage-gated sodium channel family. Characteristics of nine voltage-gated sodium channel family members: length of the protein, number of IDR regions, average prediction score, number of total disordered amino acids considering the TOP-IDP score, percentage of IDRs. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Protein**} & **Length** & \multirow{2}{*}{**N.of IDR**} & **Average** & **N.of Disordered** & **Percentage** \\  & **(AA)** & & **Prediction Score** & **AA** & **of IDR** \\ \hline
**NaV1.1** & 2009 & 29 & 0.275 & 517 & 25.73 \\
**NaV1.2** & 2005 & 25 & 0.276 & 538 & 26.83 \\
**NaV1.3** & 2000 & 23 & 0.268 & 520 & 26 \\
**NaV1.4** & 1836 & 19 & 0.253 & 437 & 23.80 \\
**NaV1.5** & 2016 & 25 & 0.328 & 637 & 31.60 \\
**NaV1.6** & 1980 & 24 & 0.268 & 504 & 25.45 \\
**NaV1.7** & 1988 & 29 & 0.282 & 538 & 27.08 \\
**NaV1.8** & 1956 & 25 & 0.272 & 498 & 25.46 \\
**NaV1.9** & 1791 & 21 & 0.219 & 330 & 18.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Study population of patients with mutations in transmembrane domains (TDs) and intra-domain loops (IDLs). Clinical, anatomical, and electrophysiological characteristics of the 36 probands at high risk for sudden cardiac death. The average overall sequence homology of NaV1.5 with the other eight members is 71.41%. Comparison of a conserved transmembrane domain (e.g., D2) increases the homology percentage to 80.82%, whereas comparison of the four longest IDRs yields mean homology values of 43.18%, 52.00%, 51.46%, and 35.71% for IDR1, IDR2, IDR3, and IDR4, respectively (Table 3 and Supplementary Figure S2). Figure 1: NaV1.5 is the most disordered member of the voltage-gated sodium channel family. (**A**) Localization of mutations in NaV1.5 in BrS cohort. (**B**) Disorder analysis of NaV1.5: PONDR-VLXT, PONDR-VSL2B, and PONDR-VL3 prediction tools were used to determine the disorder score of NaV1.5. Any value above 0.5 indicates intrinsic disorder. (**C**) Graphical illustration of NaV1.5 structure with TDs and IDL domains.