Author Contributions: Drs Zetterberg, Andreasson, and Blennow had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Wu, Sankaranarayanan, and Simon developed the BACE1 assay. Study conception and design: Zetterberg, Wu, Sankaranarayanan, Londos, Umek, Minthon, Simon, and Blennow. Acquisition of data: Zetterberg, Hansson, Buchhave, and Londos. Analysis and interpretation of data: Zetterberg, Andreasson, Andersson, Simon, and Blennow. Drafting of the manuscript: Zetterberg. Critical revision of the manuscript for important intellectual content: Andreasson, Hansson, Wu, Sankaranarayanan, Andersson, Buchhave, Londos, Umek, Minthon, Simon, and Blennow. Statistical analysis: Zetterberg and Simon. Administrative, technical, or material support: Zetterberg, Andreasson, Hansson, Wu, Sankaranarayanan, Londos, Umek, Minthon, and Simon. Study supervision: Zetterberg, Londos, and Blennow.