For the AD, preclinical AD, and PD findings, we had the opportunity to test for observational differences between diagnostic groups in CSF biomarker levels for the proteins implicated in the MR analysis (AD: APOE, CD33 and GRN; Preclinical AD: MMP‐10; PD: CD38, GPNMB, ADAM15). Here, CD38 is linked to Parkinson disease.