The incidence of amyloid-related image abnormality of edema or effusion (ARIA-E) or amyloid-related imaging abnormalities-hemosiderin (ARIA-H) was 17% in lecanemab-treated subjects and 9% in the placebo group, especially in those who carried the homozygous ApoE4 allele. The gene discussed is APOE; the disease is amyloidosis.