The role of sodium channels in sudden unexpected death in pediatrics
Authors: Rochtus Anne M. , Goldstein Richard D. , Holm Ingrid A. , Brownstein Catherine A. , Pérez-Palma Eduardo , Lal Dennis , Poduri Annapurna H. 
Published: August 2018

Sudden Unexpected Death in Pediatrics (SUDP) is a tragic condition with hypothesized multifactorial etiology. While there is recent evidence implicating genes related to cardiac arrhythmia and epilepsy as genetic risk factors contributing to some cases of SUDP, the underlying mechanisms of SUDP remain under active investigation. SUDP encompasses Sudden Infant Death Syndrome (SIDS) and Sudden Unexplained Death in Childhood (SUDC), affecting children under and over 1 year of age, respectively. The presence of developmental hippocampal malformations in many children with SIDS and SUDC suggests that a subset of patients may share epilepsy-related mechanisms with Sudden Unexplained Death in Epilepsy Patients (SUDEP). Pathogenic variants in both epilepsy- and arrhythmia-related sodium channel genes have recently been identified in patients with SIDS, SUDC, and SUDEP.

We performed a candidate gene analysis for genes encoding sodium channel subunits in whole exome sequencing (WES) data from 73 SUDP patients. After a thorough literature review, we mapped all reported SUDP-associated sodium channel variants alongside variants from the population on a structural protein model to evaluate whether patient variants clustered in important protein domains compared to controls.

In our cohort, 13 variants met criteria for pathogenicity or potential pathogenicity. While SCN1A, SCN1B, and SCN5A have established disease associations, we also considered variants in the paralogs SCN3A, SCN4A and SCN9A. Overall, the patient-associated variants clustered at conserved amino acid sites across the sodium channel gene family that do not tolerate variation in these genes.

This study provides a molecular overview of sodium channel variants present in cases with SUDP and reveals key amino acid sites that do not tolerate variation across the SCN paralog family. Further research will lead to an improved understanding of the contribution of sodium channels to SUDP, with a goal of one day implementing prevention strategies to avoid untimely deaths in at-risk children.

Author Summary

The sudden unexplained death of an infant or a child is a tragic event, which is likely caused by the complex interaction of multiple factors. Besides environmental factors, genes related to epilepsy and cardiac arrhythmia have been identified as risk factors. The sodium channel family encompasses genes, related to both cardiac arrhythmia as well as epilepsy, whose proteins share structural homology. We evaluated sodium channel gene variants in our cohort, examined all known variants in sodium genes in SUDP patients from the literature, and mapped patient variants alongside variants from the population on a 3D protein model. The patient variants clustered at conserved amino acid sites with low rates of variation in the general population, not only in the particular gene involved but also in the gene family. This study illustrates that sodium channel variants contribute to the complex phenotype of sudden death in pediatrics, suggesting complex mechanisms of neurologic and/or cardiac dysfunction contributing to death.