HCN3 and epilepsy syndrome: In addition, a systematic review summarizing published HCN channelopathy cases reported two postmortem cases carrying rare HCN3 variants (K69R and P630L) that were classified as unclassified/unknown epileptic syndromes and died of SUDEP, raising the possibility of a link between HCN3 variation and SUDEP risk; however, evidence remains extremely limited and requires confirmation in large, well-phenotyped cohorts (37).