ABSTRACT
Objective@#To explore the effects of ApoE epsilon4 (ApoE-ε4) alleles on cognitive function and resting-state functional MRI (rs-fMRI) in patients with amnestic mild cognitive impairment(aMCI) based on a prospective cohort study.@*Methods@#An average of 20 months of prospective observations were conducted on 16 ApoE-ε4-carriers and 24 non-carriers of aMCI. Neuropsychological assessments and rs-fMRI data were collected at both baseline and follow-up. All participants were assessed by a battery of neuropsychological tests and underwent rs-fMRI. Two core regions of the default mode network (DMN), the left posterior cingulate cortex (PCC) and the medial prefrontal cortex (mPFC), were selected as seeds to calculate the functional connectivity. Two-way repeated measures analysis of variance was used to assess the effects of ApoE genotype(ε4-carriers, nonε4-carriers), interval and the interaction between these two factors for functional connectivity extracted from changed region found by t-test.Conversion rates of dementia were compared between ApoE-ε4-carriers and nonε4-carriers at follow-up using Chi-square test. For the comparison of functional connectivity and clinical data between ApoE-ε4-carriers and nonsε4-carriers in baseline and follow-up, the normal distribution test was carried out first. If the normal distribution was fitted, the two-sample t test was used, otherwise, the Mann-Whitney rank sum test was used. Finally, the general linear model was used to assess the relationships between alterations in functional connectivity and in neuropsychological assessments as well as the interaction effect.@*Results@#(1)Significant decline in memory domains were found in ApoE-ε4-carriers as compared to non-carriers at both baseline and follow-up. The ApoE-ε4-carriers (14/16) presented a higher conversation rate than non-carriers(13/24, χ2=4.862, P=0.027) at follow-up. (2)Functional imaging analysis revealed that ApoE-ε4-carriers exhibited significantly higher functional connectivity between the left PCC and the left angular (ApoE-ε4-carriers: 0.23±0.11, non-carriers: -0.03±0.13, t=4.800, cluster size: 1 944 mm3, P=0.004), and between the left mPFC and the left angular (ApoE-ε4-carriers: 0.33±0.21, non-carriers: 0.08±0.18, t=5.040, cluster size:1 836 mm3, P=0.006) as compared to non-carriers at follow-up. We detected significant effect for the interaction interval by ApoE-ε4 on functional connectivity between the left angular and the left PCC (F=10.833, P=0.002)as well as the left mPFC (F=7.280, P=0.010). (3)The alteration of functional connectivity value between the left mPFC and the left angular in ApoE-ε4-carriers was positively correlated with the changes ofimmediate memory (r=0.692, P=0.018). The correlation was not statistically significant in ApoE-ε4-noncarriers (r=-0.198, P=0.417) and the integration effect was significant (F=8.632, P=0.006).@*Conclusions@#The ApoE-ε4 actually accelerates the deterioration of cognitive function in aMCI patients and carriers presented relatively reserved functional connectivity between the left angular and other core regions within DMN, which indicated the disruption of functional connectivity may be one of the underline mechanisms of ApoE-ε4 during AD process.
ABSTRACT
Objective:To explore the effects of ApoE epsilon4 (ApoE-ε4) alleles on cognitive function and resting-state functional MRI (rs-fMRI) in patients with amnestic mild cognitive impairment(aMCI) based on a prospective cohort study.Methods:An average of 20 months of prospective observations were conducted on 16 ApoE-ε4-carriers and 24 non-carriers of aMCI. Neuropsychological assessments and rs-fMRI data were collected at both baseline and follow-up. All participants were assessed by a battery of neuropsychological tests and underwent rs-fMRI. Two core regions of the default mode network (DMN), the left posterior cingulate cortex (PCC) and the medial prefrontal cortex (mPFC), were selected as seeds to calculate the functional connectivity. Two-way repeated measures analysis of variance was used to assess the effects of ApoE genotype(ε4-carriers, nonε4-carriers), interval and the interaction between these two factors for functional connectivity extracted from changed region found by t-test.Conversion rates of dementia were compared between ApoE-ε4-carriers and nonε4-carriers at follow-up using Chi-square test. For the comparison of functional connectivity and clinical data between ApoE-ε4-carriers and nonsε4-carriers in baseline and follow-up, the normal distribution test was carried out first. If the normal distribution was fitted, the two-sample t test was used, otherwise, the Mann-Whitney rank sum test was used. Finally, the general linear model was used to assess the relationships between alterations in functional connectivity and in neuropsychological assessments as well as the interaction effect. Results:(1)Significant decline in memory domains were found in ApoE-ε4-carriers as compared to non-carriers at both baseline and follow-up. The ApoE-ε4-carriers (14/16) presented a higher conversation rate than non-carriers(13/24, χ 2=4.862, P=0.027) at follow-up. (2)Functional imaging analysis revealed that ApoE-ε4-carriers exhibited significantly higher functional connectivity between the left PCC and the left angular (ApoE-ε4-carriers: 0.23±0.11, non-carriers: -0.03±0.13, t=4.800, cluster size: 1 944 mm 3, P=0.004), and between the left mPFC and the left angular (ApoE-ε4-carriers: 0.33±0.21, non-carriers: 0.08±0.18, t=5.040, cluster size:1 836 mm 3, P=0.006) as compared to non-carriers at follow-up. We detected significant effect for the interaction interval by ApoE-ε4 on functional connectivity between the left angular and the left PCC ( F=10.833, P=0.002)as well as the left mPFC ( F=7.280, P=0.010). (3)The alteration of functional connectivity value between the left mPFC and the left angular in ApoE-ε4-carriers was positively correlated with the changes ofimmediate memory ( r=0.692, P=0.018). The correlation was not statistically significant in ApoE-ε4-noncarriers ( r=-0.198, P=0.417) and the integration effect was significant ( F=8.632, P=0.006). Conclusions:The ApoE-ε4 actually accelerates the deterioration of cognitive function in aMCI patients and carriers presented relatively reserved functional connectivity between the left angular and other core regions within DMN, which indicated the disruption of functional connectivity may be one of the underline mechanisms of ApoE-ε4 during AD process.
ABSTRACT
Objective To explore a new index for reflecting the topological information of brain functional networks in patients at high risk of Alzheimer disease using characteristics of resting-state functional connectivity strengths(FCS) in patients with amnestic mild cognitive impairment(aMCI). Methods Thirty-one aMCI patients and 42 age, gender and years of education matched normal controls were enrolled between September 2009 and April 2011 in this study. The resting-state functional MRI (rs-fMRI) data of all participants were acquired and preprocessed. Then the whole-brain functional connectivities were constructed for exploring the distribution characteristics of hub regions which had higher FCS values. Using two-sample t test to compare group differences in age, years of education and each neuropsychological assessment. In addition, using Chi-squared test to compare group differences in gender. Group differences in FCS values were analyzed by general linear model. Finally, correlation analyses were used to evaluate the relationships between the FCS values of the brain regions with group differences and behavioral scores in aMCI patients. Results The hub regions of the functional networks in the aMCI patients were mainly located in the association cortices such as the precuneuses, posterior cingulate cortices, medial prefrontal cortices, angular gyri, superior occipital gyri, fusiform gyri and lingual gyri. The distribution models in the aMCI patients were consistent with those in the normal controls. However, the FCS values of these brain regions were significantly lower in the aMCI patients than those in the normal controls. In comparison to the normal controls, the aMCI patients had significantly decreased FCS values in the bilateral fusiform gyri, lingual gyri, superior occipital gyri, left middle occipital gyrus and postcentral gyrus (the cluster was 389, 230, 187 and 107 voxels, respectively;P<0.05, respectively), and they had decreased trends of FCS values in the bilateral posterior cingulate cortices and right insulas. The correlation analysis with uncorrected conditions showed that the FCS values of the left postcentral gyri were correlatid with the clock drawing test (CDT) scores (r=0.436, P=0.026). Conclusions aMCI mainly attacks the hub regions of brain functional networks. The changes of functional connectivities in aMCI may reflect the early pathophysiologic alterations of AD.