Accelerated clinical decline in well-educated patients with frontotemporal lobar degenerations

Lifelong experiences as a proxy of cognitive reserve moderate the association between connectivity and cognition in Alzheimer's disease

Alzheimer's disease (AD) is associated with alterations in functional connectivity (FC) of the brain. The FC underpinnings of CR, that is, lifelong experiences, are largely unknown. Resting-state FC and structural MRI were performed in 76 CSF amyloid-β (Aβ) negative healthy controls and 152 Aβ positive individuals as an AD spectrum cohort (ADS; 55 with subjective cognitive decline, SCD; 52 with mild cognitive impairment; 45 with AD dementia). Following a region-of-interest (ROI) FC analysis, intrinsic network connectivity within the default-mode network (INC-DMN) and anti-correlation in INC between the DMN and dorsal attention network (DMN:DAN) were obtained as composite scores. CR was estimated by education and Lifetime Experiences Questionnaire (LEQ). The association between INC-DMN and MEM was attenuated by higher LEQ scores in the entire ADS group, particularly in SCD. In ROI analyses, higher LEQ scores were associated with higher FC within the DMN in ADS group. INC-DMN remains relatively intact despite memory decline in individuals with higher lifetime activity estimates, supporting a role for functional networks in maintaining cognitive function in AD.

Age of Symptom Onset and Longitudinal Course of Sporadic Alzheimer's Disease, Frontotemporal Dementia, and Vascular Dementia: A Systematic Review and Meta-Analysis

BACKGROUND

Understanding how the age of dementia symptom onset affects the longitudinal course of dementia can assist with prognosis and care planning.

OBJECTIVE

To synthesize evidence regarding the relationship of age of symptom onset with the longitudinal course of sporadic Alzheimer's disease (AD), vascular dementia (VaD), and frontotemporal dementia (FTD).

METHODS

We searched Medline, CINAHL, Embase, PsycINFO, PubMed, and Scopus for longitudinal studies that examined the impact of sporadic AD, VaD, or FTD symptom onset age on measures of cognition, function, or behavioral symptoms. Studies that examined age at diagnosis only were excluded. Quantitative meta-analysis was conducted where studies reported sufficient data for pooling.

RESULTS

Thirty studies met all inclusion criteria (people with AD (n = 26), FTD (n = 4)) though no studies examined VaD. Earlier onset of AD was associated with more rapid annual cognitive decline (estimate = -0.07; 95% CI -0.14 to 0.00; p = 0.045). Most studies that stratified their sample reported that younger AD onset (usually <  65 years) was associated with more rapid cognitive decline. Other evidence was inconclusive.

CONCLUSION

Younger people with AD appear to have a poorer prognosis in terms of faster cognitive decline than older people with AD. More research is required to determine the impact of symptom onset age in VaD and FTD, and on functional decline in all dementias.

Impairments in Episodic-Autobiographical Memory and Emotional and Social Information Processing in CADASIL during Mid-Adulthood

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) - is the most common genetic source of vascular dementia in adults, being caused by a mutation in NOTCH3 gene. Spontaneous de novo mutations may occur, but their frequency is largely unknown. Ischemic strokes and cognitive impairments are the most frequent manifestations, but seizures affect up to 10% of the patients. Herein, we describe a 47-year-old male scholar with a genetically confirmed diagnosis of CADASIL (Arg133Cys mutation in the NOTCH3 gene) and a seemingly negative family history of CADASIL illness, who was investigated with a comprehensive neuropsychological testing battery and neuroimaging methods. The patient demonstrated on one hand severe and accelerated deteriorations in multiple cognitive domains such as concentration, long-term memory (including the episodic-autobiographical memory domain), problem solving, cognitive flexibility and planning, affect recognition, discrimination and matching, and social cognition (theory of mind). Some of these impairments were even captured by abbreviated instruments for investigating suspicion of dementia. On the other hand the patient still possessed high crystallized (verbal) intelligence and a capacity to put forth a façade of well-preserved intellectual functioning. Although no definite conclusions can be drawn from a single case study, our findings point to the presence of additional cognitive changes in CADASIL in middle adulthood, in particular to impairments in the episodic-autobiographical memory domain and social information processing (e.g., social cognition). Whether these identified impairments are related to the patient's specific phenotype or to an ascertainment bias (e.g., a paucity of studies investigating these cognitive functions) requires elucidation by larger scale research.

Brain size and the compensation of Alzheimer's disease symptoms: a longitudinal cohort study

BACKGROUND

Greater intracranial volume (ICV) has been associated with less severe Alzheimer's disease (AD) symptoms at a given level of cerebral pathology. In this study we examine whether ICV modulates the association between clinical disease progression on the one hand and brain atrophy or the apolipoprotein E genotype on the other.

METHODS

Six hundred seventy-four subjects were studied from the AD Neuroimaging Initiative (ADNI). Subjects included 204 controls, 144 patients with AD dementia, and 326 with amnestic mild cognitive impairment (aMCI). Longitudinal analyses were conducted applying generalized estimating equations to examine the influence of ICV on clinical deterioration and atrophy progression. Follow-up data were available for up to 60 months after the baseline visit (mean 31.42 months, SD 13.12 months).

RESULTS

ICV was not directly associated with clinical worsening or atrophy progression. However, ICV attenuated the impact of atrophy and the apolipoprotein E ε4 allele on clinical disease progression in aMCI.

CONCLUSION

Greater ICV, that is, premorbid brain size, seems to protect against clinical deterioration in the face of AD-related brain atrophy in aMCI. The results support the theory of a compensatory role of brain reserve in contrast to a neuroprotective role. The protective effects of morphologic reserve seem to be limited to early clinical AD; once a certain threshold of neurodegenerative burden is passed, a larger premorbid brain no longer offers an advantage in this context.

SORL1 genetic variants and cerebrospinal fluid biomarkers of Alzheimer’s disease

The neuronal sortilin-related receptor with A-type repeats (SORL1, also called LR11 or sorLA) is involved in amyloidogenesis, and the SORL1 gene is a major risk factor for Alzheimer’s disease (AD). We investigated AD-related CSF biomarkers for associations with SORL1 genetic variants in 105 German patients with mild cognitive impairment (MCI) and AD. The homozygous CC-allele of single nucleotide polymorphism (SNP) 4 was associated with increased Tau concentrations in AD, and the minor alleles of SNP8, SNP9, and SNP10 and the haplotype CGT of these SNPs were associated with increased SORL1 concentrations in MCI. SNP22 and SNP23, and the haplotypes TCT of SNP19-21-23, and TTC of SNP22-23-24 were correlated with decreased Ab42 levels in AD. These results strengthen the functional role of SORL1 in AD.

A visual [18F]FDG-PET rating scale for the differential diagnosis of frontotemporal lobar degeneration

This study presents a visual rating scale for the assessment of cerebral [(18)F]fluoro-2-deoxy-D: -glucose positron emission tomography (FDG-PET) scans to characterize typical findings in dementias associated with frontotemporal lobar degeneration (FTLD) and to differentiate individual patients with FTLD compared to Alzheimer's disease (AD) and mild cognitive impairment (MCI). A total of 43 cerebral PET scans from patients with FTLD (n = 16, mean age 58.4 years), AD (n = 16, 59.9 years) and MCI (n = 11, 57.9 years) were analysed. Every PET data set was visually rated for seven brain regions on each hemisphere (frontal lobe, temporal lobe, parietal lobe, occipital lobe, basal ganglia, thalamus and cerebellum). The extent of the impairment in metabolism was classified as absent, mild, medium or strong. Using this four-stage visual rating scale, characteristic profiles of metabolic impairment in FTLD, AD, MCI and the FTLD-subgroup FTD (n = 9) could be demonstrated. Patients with FTLD showed a significantly lower metabolism in the left frontal lobe and in the left basal ganglia when compared to AD and to MCI. Complementary analyses using statistical parametric mapping (SPM2) supported the findings of the visual analysis. In detecting FTLD with visual rating, sensitivity/specificity was 81/94% compared to AD and 81/64% compared to MCI. Patients with FTD were correctly attributed to a diagnosis of FTLD with a sensitivity of 89%. This visual rating scale may facilitate the differential diagnosis of FTLD in clinical routine.

[Cognitive reserve and its relevance for the prevention and diagnosis of dementia]

Progressive brain damage is undoubtedly the main cause of clinical symptoms of dementia in neurodegenerative disorders such as Alzheimer's disease. However, the association between brain damage and cognitive symptoms is not linear. Certain interindividual differences such as a good school education or a greater brain volume are associated with a higher resilience against brain damage that is usually referred to as cognitive reserve (CR). Individuals with high CR have a diminished risk for dementia and both active and passive concepts for this phenomenon are discussed. In the concept of passive CR, peculiarities of brain structure such as higher synapse or neuron counts are regarded as buffers against brain damage. Symptoms of dementia do not occur until a certain threshold of damage is passed. In addition to the passive concepts, active mechanisms are also discussed that are associated with the ability to maintain a certain level of cognitive performance in the face of progressive neurodegeneration for a longer period. In subjects with healthy cognitive function, these active mechanisms contribute to the adaptation of brain activity when task difficulty level is increased. Confronted with progressive neurodegeneration, these active mechanisms help to compensate for brain damage. Individuals with higher CR show more efficient activation for solving the same task, which helps them to preserve normal levels of cognitive performance for a longer period.

Education mediates microstructural changes in bilateral hippocampus

Education has been extensively considered an influential factor in the modulation of interindividual differences in cognitive performance and cerebral structure. Consequently, education has been linked to the concept of reserve, which refers to an unspecified aspect of brain structure or function that enables people with more education to cope better with brain pathology or age-related changes. Nevertheless, the education-related neural mechanisms involved in reserve are still not completely understood. In this study, 150 healthy subjects were submitted to a comprehensive sociodemographic, clinical and cognitive assessment, and a high-resolution structural MRI and diffusion tensor imaging scan protocol. Data of micro- (mean diffusivity, MD) and macro- (volume) structural changes of six bilateral deep gray matter structures (thalamus, caudate nucleus, putamen, hippocampus, amygdala, and globus pallidus) were analyzed with reference to years of formal education. Results show that decreased MD in both left and right hippocampi was the only structural parameter that, along with decreasing age, significantly correlated with higher education. The present findings suggest that the hippocampal formation might be one site where education-mediated microstructural changes occur, possibly compensating for cognitive decline.

Predicting functional decline in behavioural variant frontotemporal dementia

Behavioural variant frontotemporal dementia is characterized by a change in comportment. It is associated with considerable functional decline over the course of the illness albeit with sometimes dramatic variability among patients. It is unknown whether any baseline features, or combination of features, could predict rate of functional decline in behavioural variant frontotemporal dementia. The aim of this study was to investigate the effects of different baseline clinical, neuropsychological, neuropsychiatric, genetic and anatomic predictors on the rate of functional decline as measured by the Clinical Dementia Rating Sum of Boxes scale. We identified 86 subjects with behavioural variant frontotemporal dementia that had multiple serial Clinical Dementia Rating Sum of Boxes assessments (mean 4, range 2-18). Atlas-based parcellation was used to generate volumes for specific regions of interest at baseline. Volumes were utilized to classify subjects into different anatomical subtypes using the advanced statistical technique of cluster analysis and were assessed as predictor variables. Composite scores were generated for the neuropsychological domains of executive, language, memory and visuospatial function. Behaviours from the brief questionnaire form of the Neuropsychiatric Inventory were assessed. Linear mixed-effects regression modelling was used to determine which baseline features predict rate of future functional decline. Rates of functional decline differed across the anatomical subtypes of behavioural variant frontotemporal dementia, with faster rates observed in the frontal dominant and frontotemporal subtypes. In addition, subjects with poorer performance on neuropsychological tests of executive, language and visuospatial function, less disinhibition, agitation/aggression and night-time behaviours at presentation, and smaller medial, lateral and orbital frontal lobe volumes showed faster rates of decline. In many instances, the effect of the predictor variables observed across all subjects was also preserved within anatomical subtypes. Furthermore, some of the predictor variables improved our prediction of rate of functional decline after anatomical subtype was taken into account. In particular, age at onset was a highly significant predictor but only after adjusting for subtype. We also found that although some predictor variables, for example gender, Mini-Mental State Examination score, and apathy/indifference, did not affect the rate of functional decline; these variables were associated with the actual Clinical Dementia Rating Sum of Boxes score estimated for any given time-point. These findings suggest that in behavioural variant frontotemporal dementia, rate of functional decline is driven by the combination of anatomical pattern of atrophy, age at onset, and neuropsychiatric characteristics of the subject at baseline.