Abstract
BackgroundAlthough structural and functional changes of the striatum and hippocampus are present in familial Alzheimer’s disease, little is known about the effects of specific gene mutation or disease progression on their related neural circuits. This study was to evaluate the effects of known pathogenic gene mutation and disease progression on the striatum- and hippocampus-related neural circuits, including frontostriatal and hippocampus-posterior cingulate cortex (PCC) pathways.MethodsA total of 102 healthy mutation non-carriers, 40 presymptomatic mutation carriers (PMC), and 30 symptomatic mutation carriers (SMC) of amyloid precursor protein (APP), presenilin 1 (PS1), or presenilin 2 gene, with T1 structural MRI, diffusion tensor imaging, and resting-state functional MRI were included. Representative neural circuits and their key nodes were obtained, including bilateral caudate-rostral middle frontal gyrus (rMFG), putamen-rMFG, and hippocampus-PCC. Volumes, diffusion indices, and functional connectivity of circuits were compared between groups and correlated with neuropsychological and clinical measures.ResultsIn PMC, APP gene mutation carriers showed impaired diffusion indices of caudate-rMFG and putamen-rMFG circuits; PS1 gene mutation carriers showed increased fiber numbers of putamen-rMFG circuit. SMC showed increased diffusivity of the left hippocampus-PCC circuit and volume reduction of all regions as compared with PMC. Imaging measures especially axial diffusivity of the representative circuits were correlated with neuropsychological measures.ConclusionsAPP and PS1 gene mutations affect frontostriatal circuits in a different manner in familial Alzheimer’s disease; disease progression primarily affects the structure of hippocampus-PCC circuit. The structural connectivity of both frontostriatal and hippocampus-PCC circuits is associated with general cognitive function. Such findings may provide further information about the imaging biomarkers for early identification and prognosis of familial Alzheimer’s disease, and pave the way for early diagnosis, gene- or circuit-targeted treatment, and even prevention.
Highlights
Structural and functional changes of the striatum and hippocampus are present in familial Alzheimer’s disease, little is known about the effects of specific gene mutation or disease progression on their related neural circuits
The major findings were that amyloid precursor protein (APP) and presenilin 1 (PS1) gene mutations affected the structure and function of the frontostriatal pathway in a different manner in presymptomatic stage, where APP primarily impaired the structural connectivity; disease progression especially affected the structure of hippocampus-posterior cingulate cortex (PCC) pathway; and structural connectivity of both frontostriatal and hippocampus-PCC circuits were associated with general cognitive function in Familial Alzheimer’s disease (FAD)
For the effect of gene mutation on the structure and function of the representative neural circuits, our results indicate that APP mutation has early deleterious effect on the structural integrity of frontostriatal neural circuits, while PS1 mutation has little or even compensatory effect on it
Summary
Structural and functional changes of the striatum and hippocampus are present in familial Alzheimer’s disease, little is known about the effects of specific gene mutation or disease progression on their related neural circuits. This study was to evaluate the effects of known pathogenic gene mutation and disease progression on the striatum- and hippocampus-related neural circuits, including frontostriatal and hippocampusposterior cingulate cortex (PCC) pathways. Circuit or network level treatments for AD have shown some promising results [4], such as deep-brain stimulation [5,6,7]. FAD includes autosomal dominant Alzheimer’s disease (ADAD), carrying known causative gene mutation including the amyloid precursor protein (APP), presenilin 1 (PS1), or presenilin 2 (PS2) that are nearly 100% certain to show sequential pre-dementia and dementia stage clinical features and can be diagnosed before symptoms onset. Treatment could be initiated at a presymptomatic stage in FAD, which promotes the development of intervention and prevention trials [10, 11]
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