Subsequent sequencing of the SCN1A gene (Swiss-Prot P35498) known to cause Dravet syndrome uncovered a heterozygous frameshift mutation (c.2675delA, p.N892fsX2) in the intracellular loop between DIIS4 and DIIS5 (Figure 6, Table 1). Here, SCN1A is linked to encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.