The interaction of APOE genotype by age in amnestic mild cognitive impairment: a voxel-based morphometric study.

The apolipoprotein E (APOE) gene has been confirmed as the major genetic risk factor for the conversion of amnestic mild cognitive impairment (aMCI) to Alzheimer's disease (AD). The present study was to assess whether there was a specific interaction of APOE by the aging process on brain morphology in aMCI. The analysis of gray matter (GM) voxel-based morphometry was performed in 85 aMCI and 100 healthy controls (HC). A significant interaction of APOE genotype by age on GM volume was found in the left calcarine, the left insula, and the left medial frontal gyrus in aMCI. GM volume in aMCI decreased significantly with ε 2-carriers < ε3/ε3 < ε4-carriers in above brain regions (except the left insula) while there was only a reduced tendency in HC. The multivariate regression analysis showed the well-known negative relationship for ε4-carriers and the positive relationship for ε2-carriers (except the left insula), while no correlations were found for ε3/ε3 between age and GM volumes on above brain regions. Moreover, the reduced GM volumes in the left calcarine and insula correlated with the impairment of visuo-spatial cognition and episodic memory in ε4- and ε2-carriers but not ε3/ε3, respectively. These results suggest that the APOE ε4 and ε2 alleles have the opposing effects on brain morphology across the spectrum of cognitive aging. Moreover, the interaction of APOE by age on brain morphology may accelerate the pathological progression of late-life cognitive decline in aMCI with ε4-carriers and delay the possible conversion from aMCI with ε2-carriers to AD.