Although the SIDS-associated p.Ser530Pro mutation demonstrated a wild-type (WT) electrophysiological phenotype when heterologously expressed, the SUDS-associated p.Val392Ile and p.Gly600Arg mutations significantly increased peak current density at +40 mV in comparison with WT by 100.4% (P < 0.05) and 50.4% (P < 0.05), respectively. p.Val392Ile also slowed recovery from inactivation 3.6-fold, indicating a mixed electrophysiological phenotype.