BACE1 and Alzheimer disease: CSF-based studies provide evidence that BACE1 biomarkers, both protein concentrations and enzymimatic activity, support further analytical and clinical investigations in patients with AD to investigate their potential as candidate biomarkers suitable for clinical practice (i.e., early diagnosis, prediction, and progression) and pharmacological trials targeting BACE1 (i.e., target engagement and efficacy response, among others).