The GEE analyses results did not change when limiting analyses to the pre‐diagnosis visits only, that is, excluding the third visits of 94 individuals who had already developed MCI or dementia at the second visit, with a rapid decrease in PCA2 comparing incident MCI/AD (β = −0.034 [95% CI: −0.06, −0.008], P = 0.010) to CU adjusted for age, sex, ethnicity, education, APOE status, and comorbidities (Model 2). The gene discussed is APOE; the disease is Alzheimer disease.