MAPT and Alzheimer disease: In the group of healthy elderly individuals, Stomrud et al. observed that the individuals with risk markers for possible future AD, that is, AD-supportive CSF biomarkers (tau and Aβ1-42) or presence of the APOE ε4 allele which is one gene shown to increase the risk of developing AD, have higher CSF MMP-3 and MMP-9 levels and a higher CSF MMP-3/TIMP-1 ratio compared with the individuals without risk markers [40].