Sudden unexplained death in childhood associated with febrile seizures (SUDC-FS) is the sudden unexplained death of a child that has a personal and family history of fever-related (febrile) seizures. These children have many features in common with individuals dying of SUDEP and SIDS, including sleep-related death and discovery in the prone position. We believe that these diseases have similar causes including gene mutations that cause seizures. There is a clear pattern of genetic inheritance in some SUDC-FS families. Genetic analysis of these families, as proposed in this study, provides an excellent opportunity to identify the genes responsible for SUDC-FS and therefore also SUDEP and SIDS. This study has the potential, therefore, to uncover novel information that could be used to diagnose and treat all individuals at risk from sudden unexpected death associated with seizure.