SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: Despite considerable effort, no phenotype-genotype correlation has been shown for the hundreds of SCN1A mutations identified, with the majority associated with Dravet syndrome and a small proportion with GEFS+.4 Here, we show a phenotype-genotype correlation for SCN1A describing a distinct SCN1A phenotype, early infantile SCN1A encephalopathy, that is far more severe than Dravet syndrome.