The cleaved, soluble form of SEZ6 (sSEZ6) is released from neurons and is found in CSF, where it is increased in depressed, bipolar, and schizophrenic patients as well as in inflammatory pain and may be a biomarker for monitoring BACE1 activity in clinical trials for AD (Maccarrone et al, 2013; Pigoni et al, 2016; Roitman et al, 2019). Here, BACE1 is linked to Alzheimer disease.