Apolipoprotein E (APOE) is the primary brain apolipoprotein which has been found to be lower in AD patient when compared to healthy controls. In addition, the APOE gene isoform, APOE e4, also has been found to be associated with an increased risk of AD. Both APOE and APOE e4 have been studied as possible biomarkers for the assessment of AD. CSF testing for APOE and the APOE e4 isoform is available commercially.
- Soluble AB Precursor Protein (sAPP):
As previously discussed, APP is an integral membrane protein whose proteolysis produces AB peptides. APP may play a role during neuroregeneration and regulation of neural activity. Recent research has shown that large soluble APP (sAPP) present in CSF may serve as a potential biomarker of AD. Although many research studies have found that the CSF levels of sAPP tend to increase in AD patients, there are some reports that there may not be any significant change or even a slight decrease. It appears that more clinical studies are needed to confirm the validity of using sAPP as a biomarker for AD.