Cortical microstructural changes along the Alzheimer's disease continuum.

INTRODUCTION: Cortical mean diffusivity (MD) and free water fraction (FW) changes are proposed biomarkers for Alzheimer's disease (AD). METHODS: We included healthy control subjects (N = 254), mild cognitive impairment (N = 41), and AD dementia (N = 31) patients. Participants underwent a lumbar puncture and a 3 T magnetic resonance imaging. Healthy control subjects were classified following National Institute on Aging-Alzheimer's Association stages (stage 0, N = 220; stage 1, N = 25; and stage 2/3, N = 9). We assessed the cortical MD, cortical FW, and cortical thickness (CTh) changes along the AD continuum. RESULTS: Microstructural and macrostructural changes show a biphasic trajectory. Stage 1 subjects showed increased CTh and decreased MD and FW with respect the stage 0 subjects. Stage 2/3 subjects showed decreased CTh and increased cortical MD and FW, changes that were more widespread in symptomatic stages. DISCUSSION: These results support a biphasic model of changes in AD, which could affect the selection of patients for clinical trials and the use of magnetic resonance imaging as a surrogate marker of disease modification.

Cerebral amyloid angiopathy in Down syndrome and sporadic and autosomal-dominant Alzheimer's disease.

INTRODUCTION: We aimed to investigate if cerebral amyloid angiopathy (CAA) is more frequent in genetically determined than in sporadic early-onset forms of Alzheimer's disease (AD) (early-onset AD [EOAD]). METHODS: Neuroimaging features of CAA, apolipoprotein (APOE), and cerebrospinal fluid amyloid ß (Aß) 40 levels were studied in subjects with Down syndrome (DS, n = 117), autosomal-dominant AD (ADAD, n = 29), sporadic EOAD (n = 42), and healthy controls (n = 68). RESULTS: CAA was present in 31%, 38%, and 12% of cognitively impaired DS, symptomatic ADAD, and sporadic EOAD subjects and in 13% and 4% of cognitively unimpaired DS individuals and healthy controls, respectively. APOE ε4 genotype was borderline significantly associated with CAA in sporadic EOAD (P = .06) but not with DS or ADAD. There were no differences in Aß040 levels between groups or between subjects with and without CAA. DISCUSSION: CAA is more frequently found in genetically determined AD than in sporadic EOAD. Cerebrospinal fluid Aß40 levels are not a useful biomarker for CAA in AD.

Cerebrospinal fluid ß-amyloid and phospho-tau biomarker interactions affecting brain structure in preclinical Alzheimer disease.

OBJECTIVE: To assess the relationships between core cerebrospinal fluid (CSF) biomarkers and cortical thickness (CTh) in preclinical Alzheimer disease (AD). METHODS: In this cross-sectional study, normal controls (n = 145) from the Alzheimer's Disease Neuroimaging Initiative underwent structural 3T magnetic resonance imaging (MRI) and lumbar puncture. CSF ß-amyloid1-42 (Aß) and phospho-tau181p (p-tau) levels were measured by Luminex assays. Samples were dichotomized using published cutoffs (Aß(+) /Aß(-) and p-tau(+) /ptau(-)). CTh was measured by Freesurfer. CTh difference maps were derived from interaction and correlation analyses. Clusters from the interaction analysis were isolated to analyze the directionality of the interaction by analysis of covariance. RESULTS: We found a significant biomarker interaction between CSF Aß and CSF p-tau levels affecting brain structure. Cortical atrophy only occurs in subjects with both Aß(+) and p-tau(+). The stratified correlation analyses showed that the relationship between p-tau and CTh is modified by Aß status and the relationship between Aß and CTh is modified by p-tau status. p-Tau-dependent thinning was found in different cortical regions in Aß(+) subjects but not in Aß(-) subjects. Cortical thickening was related to decreasing CSF Aß values in the absence of abnormal p-tau, but no correlations were found in p-tau(+) subjects. INTERPRETATION: Our data suggest that interactions between biomarkers in AD result in a 2-phase phenomenon of pathological cortical thickening associated with low CSF Aß, followed by atrophy once CSF p-tau becomes abnormal. These interactions should be considered in clinical trials in preclinical AD, both when selecting patients and when using MRI as a surrogate marker of efficacy.

Rapidly progressive dementia: experience in a tertiary care medical center.

Diagnosis of rapidly progressive dementia (RPD) poses a complex medical challenge that requires an exhaustive evaluation. Although prion diseases, in particular Creutzfeldt-Jakob disease (CJD), are often suspected, many other nonprion diseases may present as RPD. Our aim was to review the causes of RPD in our center to better understand the underlying conditions. We reviewed clinical, neuroimaging, and cerebrospinal fluid data from patients with RPD admitted to our hospital from 1994 to 2009. Forty-nine patients (mean age at onset 72.4 y) with RPD were admitted to our center during the study period. The mean interval between the onset of symptoms and admission was 4.6 months. The final clinical diagnoses were as follows: nonprion neurodegenerative diseases (36.8%), CJD (30.6%), vascular dementia (8.2%), toxic-metabolic conditions (8.2%), and other disorders (16.2%). Among cases with informed death (n = 19), the average survival time was 8.6 ± 9.5 months. Survival was shorter among patients with prion disease (n = 10) than in those with other diagnoses (n = 9, P = 0.004). In conclusion, nonprion neurodegenerative diseases are the most common cause of RPD in our center. Our results suggest that although CJD is often suspected as a cause of RPD, its frequency depends on the referral differences across specialized centers.

Defective involuntary attention to novelty in type 1 diabetes and impaired awareness of hypoglycaemia.

AIM: To determine if there are differences in terms of neurophysiology and neurocognitive functioning in a group of type 1 diabetes (T1D) patients regarding hypoglycaemia awareness. METHODS: 27 patients with T1D were classified according to Clarke score as having impaired awareness of hypoglycaemia (IAH; n = 11) or normal awareness to hypoglycaemia (NAH; n = 16). We measured several clinical and sociodemographic variables and cognitive performance using neuropsychological tests. Electroencephalography was assessed during an auditory oddball task. We compared the groups in terms of clinical/sociodemographic variables as well as two event-related brain potentials (ERPs): The P3a which is associated with automatic orientation of attention to novelty, and the P3b which is associated with target detection and processing. RESULTS: The IAH group performed significantly worse on the Trail Making Test part A (TMT-A) (p = 0.05). Compared to the NAH group, P3a and P3b amplitudes in the frontal-central sites were significantly lower in the IAH group (p < 0.05). The P3a was strongly associated with worse performance on the TMT-A in the IAH group (r = 0.540; p < 0.005) CONCLUSION: IAH is accompanied by decreased neurophysiological activity in ERPs associated with information processing and with the automatic orientation of attention to novelty and environmental changes. These findings suggest a possible framework to better understand the cognitive origin of IAH in this patient population.

Plasma glial fibrillary acidic protein and neurofilament light chain for the diagnostic and prognostic evaluation of frontotemporal dementia.

BACKGROUND: Astrocytes play an essential role in neuroinflammation and are involved in the pathogenesis of neurodenegerative diseases. Studies of glial fibrillary acidic protein (GFAP), an astrocytic damage marker, may help advance our understanding of different neurodegenerative diseases. In this study, we investigated the diagnostic performance of plasma GFAP (pGFAP), plasma neurofilament light chain (pNfL) and their combination for frontotemporal dementia (FTD) and Alzheimer's disease (AD) and their clinical utility in predicting disease progression. METHODS: pGFAP and pNfL concentrations were measured in 72 FTD, 56 AD and 83 cognitively normal (CN) participants using the Single Molecule Array technology. Of the 211 participants, 199 underwent cerebrospinal (CSF) analysis and 122 had magnetic resonance imaging. We compared cross-sectional biomarker levels between groups, studied their diagnostic performance and assessed correlation between CSF biomarkers, cognitive performance and cortical thickness. The prognostic performance was investigated, analyzing cognitive decline  through group comparisons by tertile. RESULTS: Unlike pNfL, which was increased similarly in both clinical groups, pGFAP was increased in FTD but lower than in AD (all P < 0.01). Combination of both plasma markers improved the diagnostic performance to discriminate FTD from AD (area under the curve [AUC]: combination 0.78; pGFAP 0.7; pNfL 0.61, all P < 0.05). In FTD, pGFAP correlated with cognition, CSF and plasma NfL, and cortical thickness (all P < 0.05). The higher tertile of pGFAP was associated with greater change in MMSE score and poor cognitive outcome during follow-up both in FTD (1.40 points annually, hazard ratio [HR] 3.82, P < 0.005) and in AD (1.20 points annually, HR 2.26, P < 0.005). CONCLUSIONS: pGFAP and pNfL levels differ in FTD and AD, and their combination is useful for distinguishing between the two diseases. pGFAP could also be used to track disease severity and predict greater cognitive decline during follow-up in patients with FTD.

Cortical microstructure in the amyotrophic lateral sclerosis-frontotemporal dementia continuum.

OBJECTIVE: To characterize the cortical macrostructure and microstructure of behavioral and cognitive changes along the amyotrophic lateral sclerosis (ALS)-frontotemporal dementia (FTD) continuum. METHODS: We prospectively recruited 88 participants with a 3T MRI structural and diffusion-weighted imaging sequences: 31 with ALS, 20 with the behavioral variant of FTD (bvFTD), and 37 cognitively normal controls. Participants with ALS underwent a comprehensive cognitive and behavioral assessment and were dichotomized into ALS without cognitive or behavioral impairment (ALSno-cbi; n = 12) and ALS with cognitive or behavioral impairment (ALScbi; n = 19). We computed cortical thickness and cortical mean diffusivity using a surface-based approach and explored the cortical correlates of cognitive impairment with the Edinburgh Cognitive and Behavioral ALS Screen. RESULTS: The ALSno-cbi and ALScbi groups showed different patterns of reduced cortical thickness and increased cortical mean diffusivity. In the ALSno-cbi group, cortical thinning was restricted mainly to the dorsal motor cortex. In contrast, in the ALScbi group, cortical thinning was observed primarily on frontoinsular and temporal regions bilaterally. There were progressive cortical mean diffusivity changes along the ALSno-cbi, ALScbi, and bvFTD clinical continuum. Participants with ALS with either cognitive or behavioral impairment showed increased cortical mean diffusivity in the prefrontal cortex in the absence of cortical thickness. CONCLUSIONS: Cortical mean diffusivity might be a useful biomarker for the study of extramotor cortical neurodegeneration in the ALS-FTD clinical spectrum. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that the cortical microstructure correlates with cognitive impairment in the ALS-FTD continuum.

APP-derived peptides reflect neurodegeneration in frontotemporal dementia.

OBJECTIVE: We aimed to investigate the relationship between cerebrospinal fluid levels (CSF) of amyloid precursor protein (APP)-derived peptides related to the amyloidogenic pathway, cortical thickness, neuropsychological performance, and cortical gene expression profiles in frontotemporal lobar degeneration (FTLD)-related syndromes, Alzheimer's disease (AD), and healthy controls. METHODS: We included 214 participants with CSF available recruited at two centers: 93 with FTLD-related syndromes, 57 patients with AD, and 64 healthy controls. CSF levels of amyloid ß (Aß)1-42, Aß1-40, Aß1-38, and soluble ß fragment of APP (sAPPß) were centrally analyzed. We compared CSF levels of APP-derived peptides between groups and, we studied the correlation between CSF biomarkers, cortical thickness, and domain-specific cognitive composites in each group. Then, we explored the relationship between cortical thickness, CSF levels of APP-derived peptides, and regional gene expression profile using a brain-wide regional gene expression data in combination with gene set enrichment analysis. RESULTS: The CSF levels of Aß1-40, Aß1-38, and sAPPß were lower in the FTLD-related syndromes group than in the AD and healthy controls group. CSF levels of all APP-derived peptides showed a positive correlation with cortical thickness and the executive cognitive composite in the FTLD-related syndromes group but not in the healthy control or AD groups. In the cortical regions where we observed a significant association between cortical thickness and CSF levels of APP-derived peptides, we found a reduced expression of genes related to synaptic function. INTERPRETATION: APP-derived peptides in CSF may reflect FTLD-related neurodegeneration. This observation has important implications as Aß1-42 levels are considered an indirect biomarker of cerebral amyloidosis.

APOE-by-sex interactions on brain structure and metabolism in healthy elderly controls.

BACKGROUND: The APOE effect on Alzheimer Disease (AD) risk is stronger in women than in men but its mechanisms have not been established. We assessed the APOE-by-sex interaction on core CSF biomarkers, brain metabolism and structure in healthy elderly control individuals (HC). METHODS: Cross-sectional study. HC from the Alzheimer's Disease Neuroimaging Initiative with available CSF (n = 274) and/or 3T-MRI (n = 168) and/or a FDG-PET analyses (n = 328) were selected. CSF amyloid-ß1-42 (Aß1-42), total-tau (t-tau) and phospho-tau (p-tau181p) levels were measured by Luminex assays. We analyzed the APOE-by-sex interaction on the CSF biomarkers in an analysis of covariance (ANCOVA). FDG uptake was analyzed by SPM8 and cortical thickness (CTh) was measured by FreeSurfer. FDG and CTh difference maps were derived from interaction and group analyses. RESULTS: APOE4 carriers had lower CSF Aß1-42 and higher CSF p-tau181p values than non-carriers, but there was no APOE-by-sex interaction on CSF biomarkers. The APOE-by-sex interaction on brain metabolism and brain structure was significant. Sex stratification showed that female APOE4 carriers presented widespread brain hypometabolism and cortical thinning compared to female non-carriers whereas male APOE4 carriers showed only a small cluster of hypometabolism and regions of cortical thickening compared to male non-carriers. CONCLUSIONS: The impact of APOE4 on brain metabolism and structure is modified by sex. Female APOE4 carriers show greater hypometabolism and atrophy than male carriers. This APOE-by-sex interaction should be considered in clinical trials in preclinical AD where APOE4 status is a selection criterion.