NRGN and Alzheimer disease: High CSF Ng levels were related to low hippocampal volumes in the MCI ε4− (β = −0.39, p = 0.007), the MCI ε4+ (β = −0.25, p = 0.036), and the AD ε4+ (β = −0.42, p = 0.003) (Figure 6C), but in the AD ε4− and other groups, no such associations were found (Figure 6C).