SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: With onset in the first year of life, de novo heterozygous missense mutations in SCN1A, which encodes the pore-forming α1 subunit of the sodium channel, are found in about 95% of patients with Dravet syndrome (Vadlamudi et al., 2010).