CHD2 and Angelman syndrome: In a retrospective analysis of 510 individuals with genetic DEE, including pathogenic variants in SCN1A, SCN2A, SCN8A, SYNGAP1, NEXMIF, CHD2, PCDH19, STXBP1, GRIN2A, KCNT1 and KCNQ2, and Angelman syndrome, Donnan et al reported 8% of deaths, producing a mortality rate of 6.1 per 1000 person-years (95% CI 4.4 to 8.3).3