Among DEEs, the highest incidence was for infantile spasms syndrome, 30.7 per 100 000 live births (95% CI 22.9 to 40.2) [genetic aetiologies identified in 22/52 (42%), including trisomy 21 (n=6), and pathogenic variants in CDKL5 (n=2), TSC1 (n=2), TSC2 (n=3)], followed by early infantile DEE (<3 months), 10 per 100 000 live births (95% CI 5.8 to 16.0) [genetic aetiologies identified in 12/17 (70.5%), including pathogenic variants in CDKL5 (n=2)], and Dravet syndrome, 6.5 per 100 000 live births (95% CI 3.2 to 10.0), caused by SCN1A pathogenic variants in all individuals (n=11). The gene discussed is SCN1A; the disease is encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.