Background Mutations in the presenilin (PSEN1, PSEN2) and amyloid precursor protein (APP) genes cause familial Alzheimer's disease (FAD) in a nearly fully penetrant, autosomal dominant manner, providing a unique opportunity to study presymptomatic individuals who can be predicted to develop Alzheimer's disease (AD) with essentially 100% certainty. Using tensor-based morphometry (TBM), we examined brain volume differences between presymptomatic and symptomatic FAD mutation carriers and non-carrier (NC) relatives.
Methods Twenty-five mutation carriers and 10 NC relatives underwent brain MRI and clinical assessment. Four mutation carriers had dementia (MUT-Dem), 12 had amnestic mild cognitive impairment (MUT-aMCI) and nine were cognitively normal (MUT-Norm). TBM brain volume maps of MUT-Norm, MUT-aMCI and MUT-Dem subjects were compared to NC subjects.
Results MUT-Norm subjects exhibited significantly smaller volumes in the thalamus, caudate and putamen. MUT-aMCI subjects had smaller volumes in the thalamus, splenium and pons, but not in the caudate or putamen. MUT-Dem subjects demonstrated smaller volumes in temporal, parietal and left frontal regions. As non-demented carriers approached the expected age of dementia diagnosis, this was associated with larger ventricular and caudate volumes and a trend towards smaller temporal lobe volume.
Conclusions Cognitively intact FAD mutation carriers had lower thalamic, caudate and putamen volumes, and we found preliminary evidence for increasing caudate size during the predementia stage. These regions may be affected earliest during prodromal stages of FAD, while cortical atrophy may occur in later stages, when carriers show cognitive deficits. Further studies of this population will help us understand the progression of neurobiological changes in AD.
"On the other hand, emerging evidence from recent amyloid imaging studies indicates that subcortical areas, such as the striatum and thalamus, are more vulnerable to amyloid-b accumulation during early stages of familial Alzheimer's disease (Klunk et al., 2007; Koivunen et al., 2008; Remes et al., 2008; Villemagne et al., 2009; Knight et al., 2011). Though it is not yet clear whether such differences in region-specific amyloid-b accumulation impact neuropathological processes and clinical symptoms , recent functional MRI studies provide evidence of neurodegeneration in subcortical areas in presymptomatic stages of familial Alzheimer's disease due to PSEN1 mutations (Lee et al., 2013; Ryan et al., 2013). Of note, several case studies of familial Alzheimer's disease had noted frequent atypical clinical signs and symptoms, some of which could be associated with subcortical dysfunction (Rossor et al., 1993; Cabrejo et al., 2006; Larner and Doran, 2006, 2009). "
[Show abstract][Hide abstract] ABSTRACT: Recent studies suggest that subcortical structures, including striatum, are vulnerable to amyloid-β accumulation and other neuropathological features in familial Alzheimer's disease due to autosomal dominant mutations. We explored differences between familial and sporadic Alzheimer's disease that might shed light on their respective pathogenic mechanisms. To this end, we analysed 12 brain regions, including neocortical, limbic and subcortical areas, from post-mortem brains of familial Alzheimer's disease (n = 10; age at death: 50.0 ± 8.6 years) with mutations in amyloid precursor protein (APP) or presenilin 1 (PSEN1), sporadic Alzheimer's disease (n = 19; age at death: 84.7 ± 7.8 years), neurologically normal elderly without amyloid-β accumulation (normal ageing; n = 13, age at death: 82.9 ± 10.8 years) and neurologically normal elderly with extensive cortical amyloid-β deposits (pathological ageing; n = 15; age at death: 92.7 ± 5.9 years). The levels of amyloid-β40, amyloid-β42, APP, apolipoprotein E, the synaptic marker PSD95 (now known as DLG4), the astrocyte marker GFAP, other molecules related to amyloid-β metabolism, and tau were determined by enzyme-linked immunosorbent assays. We observed that familial Alzheimer's disease had disproportionate amyloid-β42 accumulation in subcortical areas compared with sporadic Alzheimer's disease, whereas sporadic Alzheimer's disease had disproportionate amyloid-β42 accumulation in cortical areas compared to familial Alzheimer's disease. Compared with normal ageing, the levels of several proteins involved in amyloid-β metabolism were significantly altered in both sporadic and familial Alzheimer's disease; however, such changes were not present in pathological ageing. Among molecules related to amyloid-β metabolism, the regional distribution of PSD95 strongly correlated with the regional pattern of amyloid-β42 accumulation in sporadic Alzheimer's disease and pathological ageing, whereas the regional distribution of APP as well as β-C-terminal fragment of APP were strongly associated with the regional pattern of amyloid-β42 accumulation in familial Alzheimer's disease. Apolipoprotein E and GFAP showed negative regional association with amyloid-β (especially amyloid-β40) accumulation in both sporadic and familial Alzheimer's disease. Familial Alzheimer's disease had greater striatal tau pathology than sporadic Alzheimer's disease. In a retrospective medical record review, atypical signs and symptoms were more frequent in familial Alzheimer's disease compared with sporadic Alzheimer's disease. These results suggest that disproportionate amyloid-β42 accumulation in cortical areas in sporadic Alzheimer's disease may be mediated by synaptic processes, whereas disproportionate amyloid-β42 accumulation in subcortical areas in familial Alzheimer's disease may be driven by APP and its processing. Region-specific amyloid-β42 accumulation might account for differences in the relative amounts of tau pathology and clinical symptoms in familial and sporadic Alzheimer's disease.
"They are known to be significantly atrophied in sporadic Alzheimer's disease but it is not known how early this atrophy occurs (de Jong et al., 2008). A recent familial Alzheimer's disease study reported decreased volumes of thalamus, caudate and putamen in presymptomatic mutation carriers who were on average 15 years younger than their family's median age at dementia diagnosis , with a trend towards increasing caudate size in those with memory deficits who were 10 years younger (Lee et al., 2013). Increased caudate volumes were reported in another cohort of presymptomatic mutation carriers who were approximately a decade younger than their expected age at symptom onset (Fortea et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: Amyloid imaging studies of presymptomatic familial Alzheimer's disease have revealed the striatum and thalamus to be the earliest sites of amyloid deposition. This study aimed to investigate whether there are associated volume and diffusivity changes in these subcortical structures during the presymptomatic and symptomatic stages of familial Alzheimer's disease. As the thalamus and striatum are involved in neural networks subserving complex cognitive and behavioural functions, we also examined the diffusion characteristics in connecting white matter tracts. A cohort of 20 presenilin 1 mutation carriers underwent volumetric and diffusion tensor magnetic resonance imaging, neuropsychological and clinical assessments; 10 were symptomatic, 10 were presymptomatic and on average 5.6 years younger than their expected age at onset; 20 healthy control subjects were also studied. We conducted region of interest analyses of volume and diffusivity changes in the thalamus, caudate, putamen and hippocampus and examined diffusion behaviour in the white matter tracts of interest (fornix, cingulum and corpus callosum). Voxel-based morphometry and tract-based spatial statistics were also used to provide unbiased whole-brain analyses of group differences in volume and diffusion indices, respectively. We found that reduced volumes of the left thalamus and bilateral caudate were evident at a presymptomatic stage, together with increased fractional anisotropy of bilateral thalamus and left caudate. Although no significant hippocampal volume loss was evident presymptomatically, reduced mean diffusivity was observed in the right hippocampus and reduced mean and axial diffusivity in the right cingulum. In contrast, symptomatic mutation carriers showed increased mean, axial and in particular radial diffusivity, with reduced fractional anisotropy, in all of the white matter tracts of interest. The symptomatic group also showed atrophy and increased mean diffusivity in all of the subcortical grey matter regions of interest, with increased fractional anisotropy in bilateral putamen. We propose that axonal injury may be an early event in presymptomatic Alzheimer's disease, causing an initial fall in axial and mean diffusivity, which then increases with loss of axonal density. The selective degeneration of long-coursing white matter tracts, with relative preservation of short interneurons, may account for the increase in fractional anisotropy that is seen in the thalamus and caudate presymptomatically. It may be owing to their dense connectivity that imaging changes are seen first in the thalamus and striatum, which then progress to involve other regions in a vulnerable neuronal network.
[Show abstract][Hide abstract] ABSTRACT: Dementias are the most common neurodegenerative diseases and they are increasingly becoming a major public health problem. The most common form of dementia, affecting over 20 million people worldwide, is Alzheimer’s disease (AD). AD is a neurodegenerative disease of the central nervous system mainly found in older adults, with an incidence that increases with age. With the development of newer technologies, including genetic screening technologies and PET/MRI scanning, the role of genetic studies and neuroimaging is being redefined; indeed, these approaches are able to provide support not only in the clinical diagnosis of dementia, but also in its presymptomatic evaluation. Many researchers agree that early identification of AD, before abnormal accumulation of amyloid and tau proteins, could provide an opportunity to hinder the progression of the disease. [18F]2-fluoro-2-deoxy-d-glucose (FDG) PET studies have shown that decreased glucose metabolism in AD precedes clinical diagnosis and that the degree of clinical disability in AD correlates closely with the magnitude of the reduction in brain glucose metabolism. Data on presymptomatic mutation carriers from families with known early-onset autosomal dominant AD (familial AD) show reductions in the cerebral metabolic rate of glucose (CMRglc), consistent with the expected AD PET pattern, in the absence of severe atrophy on MRI. These results suggest that PET CMRglc measures have the potential to serve as preclinical biomarkers of dementia, useful also for tracking disease progression. This review highlights the role of genetics and FDG PET in understanding the pathogenesis of dementia.
Shawn Kile, William Au, Carol Parise, Kimberley Rose, Tammy Donnel, Andrea Hankins, Matthew Chan, Azad Ghassemi
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