APOE ε4 allele frequency was greater in sEOAD and sLOAD compared to APPdup, missense APP mutations, DS and controls, and varied between each of the CAA phenotypes with APOE ε4 homozygosity being more commonly associated with type 3 CAA than types 1 and 2 CAA in sLOAD and sEOAD. This evidence concerns the gene APOE and Dravet syndrome.