SCN5A and long QT syndrome 3: Mutations in the α subunit encoding gene, SCN5A, are found in 5.2% of the SIDS victims (Table 6, Figure 8(a)), in accordance with the severe symptoms in children with LQT3 [118] and the observation in adults that LQT3 has the most severe clinical events [117] and that these events tend to occur during sleep [243], as in SIDS.