The best-studied biomarkers of Alzheimer’s disease (AD) are the pathologically linked CSF proteins β-amyloid 42 (Aβ1–42), total tau (t-tau), and tau phosphorylated on amino acid 181 (p-tau181). Many laboratories measure these proteins using Enzyme-Linked ImmunoSorbent Assay (ELISA). Multiplex xMAP Luminex is a semi-automated assay platform with reduced intra-sample variance, which could facilitate its use in CLIA-approved clinical laboratories. CSF concentrations of these three biomarkers reported using xMAP technology differ from those measured by the most commonly used ELISA, confounding attempts to compare results. To develop a model for converting between xMAP and ELISA levels of the three biomarkers, we analyzed CSF samples from 140 subjects (59 AD, 30 controls, 34 with mild cognitive impairment (MCI), and 17 with Parkinson Disease, including 1 with dementia). Log-transformation of ELISA and xMAP levels made the variance constant in all three biomarkers and improved the linear regression: t-tau concentrations were highly correlated (r=0.94); p-tau181 concentrations by ELISA can be better predicted using both the t-tau and p-tau181 xMAP values (r=0.96) as compared to p-tau181 concentrations alone (r=0.82); correlation of Aβ1–42 concentrations was relatively weaker but still high (r=0.77). Among all six protein/assay combinations, xMAP Aβ1–42 had the best accuracy for diagnostic classification (88%) between AD and control subjects. In conclusion, our study demonstrates that multiplex xMAP is an appropriate assay platform providing results that can be correlated with research-based ELISA values, facilitating the incorporation of this diagnostic biomarker into routine clinical practice.
Enzyme-Linked Immunosorbent Assay (ELISA); Cerebrospinal fluid (CSF); Alzheimer’s Disease
This study measured distortions of memory during short-term memory (STM) and long-term memory (LTM) versions of a semantically-associated word list learning paradigm. Performance of patients with mild-to-moderate Alzheimer’s disease (AD; MMSE ≥ 16) was compared to performance of age-matched, healthy older adult participants.
In a STM version of the Deese-Roediger-McDermott (DRM) task, participants viewed four-word lists and were prompted for recall after a brief interval. The LTM task tested recall memory for 12-word lists.
Compared to the healthy group, the AD participants show greater impairment on the LTM task than on the STM task, although veridical recall is significantly reduced on both tasks. Furthermore, on both memory tasks: a) Participants with AD generate more nonsemantic intrusions than healthy older adult participants; b) semantic intrusion rate, when computed as a proportion of total recall, does not differ between groups. Notably, nonsemantic intrusions are consistently high for AD participants across both STM and LTM despite a marked difference in recall accuracy (65% and 23%, respectively).
STM impairment with some preserved semantic processing is evident in AD. The extent and variety of intrusions reported by AD participants indicates a breakdown in their ability to monitor and constrain their recall responses, even within seconds of initial learning.
Alzheimer’s disease; false memory; short-term memory; long-term memory; semantic memory
To evaluate whether antioxidant supplements presumed to target specific cellular compartments affected cerebrospinal fluid (CSF) biomarkers.
Double-blind, placebo-controlled clinical trial.
Academic medical centers.
Subjects with mild to moderate Alzheimer disease.
Random assignment to treatment for 16 weeks with 800 IU/d of vitamin E (α-tocopherol) plus 500 mg/d of vitamin C plus 900 mg/d of α-lipoic acid (E/C/ALA); 400 mg of coenzyme Q 3 times/d; or placebo.
Main Outcome Measures
Changes from baseline to 16 weeks in CSF biomarkers related to Alzheimer disease and oxidative stress, cognition (Mini-Mental State Examination), and function (Alzheimer’s Disease Cooperative Study Activities of Daily Living Scale).
Seventy-eight subjects were randomized; 66 provided serial CSF specimens adequate for biochemical analyses. Study drugs were well tolerated, but accelerated decline in Mini-Mental State Examination scores occurred in the E/C/ALA group, a potential safety concern. Changes in CSF Aβ42, tau, and P-tau181 levels did not differ between the 3 groups. Cerebrospinal fluid F2-isoprostane levels, an oxidative stress biomarker, decreased on average by 19% from baseline to week 16 in the E/C/ALA group but were unchanged in the other groups.
Antioxidants did not influence CSF biomarkers related to amyloid or tau pathology. Lowering of CSF F2-isoprostane levels in the E/C/ALA group suggests reduction of oxidative stress in the brain. However, this treatment raised the caution of faster cognitive decline, which would need careful assessment if longer-term clinical trials are conducted.
clinicaltrials.gov Identifier: NCT00117403
Pathologic TAR-DNA-binding protein 43 (TDP-43) is a disease protein in frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis. We studied the presence, frequency, and distribution of TDP-43 pathology by immunohistochemistry and biochemistry in a series of clinically well-characterized tauopathy patient brains, including 182 Alzheimer disease (AD), 39 corticobasal degeneration, 77 progressive supranuclear palsy, and 12 Pick disease cases and investigated the clinical impact of concomitant TDP-43 pathology in these cases. TAR-DNA-binding protein 43 pathology was found in 25.8% of AD cases. It was restricted to the dentate gyrus and entorhinal cortex in approximately 75% of cases; approximately 25% showed more widespread TDP-43 pathology in frontal and temporal cortices, resembling the FTLD-U subtype associated with progranulin mutations. TAR-DNA-binding protein 43 pathology in AD was associated with significantly longer disease duration, but there was no association with the clinical presentation (148 cases diagnosed as AD and 34 cases diagnosed as frontotemporal lobar degeneration). Progressive supranuclear palsy and Pick disease cases showed no TDP-43 inclusions and no biochemical alterations of TDP-43. There was, however, a unique, predominantly glial TDP-43 pathology with staining of astrocytic plaque-like structures and coiled bodies in 15.4% of corticobasal degeneration cases; this was associated with biochemical TDP-43 changes similar to those in FTLD-U. These findings provide further insight into the burden and clinical significance of TDP-43 pathology in disorders other than FTLD-U and amyotrophic lateral sclerosis.
Alzheimer disease; Corticobasal degeneration; Frontotemporal dementia; Tauopathy; TDP-43
Florbetapir F 18 (18F-AV-45) is a positron emission tomography (PET) imaging ligand for the detection of amyloid aggregation associated with Alzheimer’s disease. Earlier data showed that florbetapir F 18 binds with high affinity to β-amyloid plaques in human brain homogenates (Kd = 3.7 nM) and has favorable imaging pharmacokinetic properties, including rapid brain penetration and washout. The present study used human autopsy brain tissue to evaluate the correlation between in vitro florbetapir F 18 binding and β-amyloid density measured by established neuropathological methods.
The localization and density of florbetapir F 18 binding in frozen and formalin-fixed paraffin-embedded sections of postmortem brain tissue from 40 subjects with a varying degree of neurodegenerative pathology was assessed by standard florbetapir F 18 autoradiography and correlated with the localization and density of β-amyloid identified by silver staining, thioflavin S staining, and immunohistochemistry.
There were strong quantitative correlations between florbetapir F 18 tissue binding and both β-amyloid plaques identified by light microscopy (sliver staining and thioflavin S fluorescence) and by immunohistochemical measurements of β-amyloid using three antibodies recognizing different epitopes of the β-amyloid peptide (Aβ). Florbetapir F 18 did not bind to neurofibrillary tangles.
Florbetapir F 18 selectively binds β-amyloid in human brain tissue. The binding intensity was quantitatively correlated with the density of β-amyloid plaques identified by standard neuropathological techniques and correlated with the density of Aβ measured by immunohistochemistry. Since β-amyloid plaques are a defining neuropathological feature for Alzheimer’s disease, these results support the use of florbetapir F 18 as an amyloid PET ligand to identify the presence of AD pathology in patients with signs and symptoms of progressive late-life cognitive impairment.
PET imaging; Alzheimer’s disease; β-amyloid plaque; autoradiography; β-amyloid; amyloid PET imaging; florbetapir F 18; 18F-AV-45; postmortem
Research suggests overlap in brain regions undergoing neurodegeneration in Parkinson's and Alzheimer's disease. To assess the clinical significance of this, we applied a validated Alzheimer's disease-spatial pattern of brain atrophy to patients with Parkinson's disease with a range of cognitive abilities to determine its association with cognitive performance and decline. At baseline, 84 subjects received structural magnetic resonance imaging brain scans and completed the Dementia Rating Scale-2, and new robust and expanded Dementia Rating Scale-2 norms were applied to cognitively classify participants. Fifty-nine non-demented subjects were assessed annually with the Dementia Rating Scale-2 for two additional years. Magnetic resonance imaging scans were quantified using both a region of interest approach and voxel-based morphometry analysis, and a method for quantifying the presence of an Alzheimer's disease spatial pattern of brain atrophy was applied to each scan. In multivariate models, higher Alzheimer's disease pattern of atrophy score was associated with worse global cognitive performance (β = −0.31, P = 0.007), including in non-demented patients (β = −0.28, P = 0.05). In linear mixed model analyses, higher baseline Alzheimer's disease pattern of atrophy score predicted long-term global cognitive decline in non-demented patients [F(1, 110) = 9.72, P = 0.002], remarkably even in those with normal cognition at baseline [F(1, 80) = 4.71, P = 0.03]. In contrast, in cross-sectional and longitudinal analyses there was no association between region of interest brain volumes and cognitive performance in patients with Parkinson's disease with normal cognition. These findings support involvement of the hippocampus and parietal–temporal cortex with cognitive impairment and long-term decline in Parkinson's disease. In addition, an Alzheimer's disease pattern of brain atrophy may be a preclinical biomarker of cognitive decline in Parkinson's disease.
Alzheimer's disease; dementia; mild cognitive impairment; Parkinson's disease; neurodegeneration
The functional diversity of a community can influence ecosystem functioning and reflects assembly processes. The large number of disparate metrics used to quantify functional diversity reflects the range of attributes underlying this concept, generally summarized as functional richness, functional evenness, and functional divergence. However, in practice, we know very little about which attributes drive which ecosystem functions, due to a lack of field-based tests. Here we test the association between eight leading functional diversity metrics (Rao’s Q, FD, FDis, FEve, FDiv, convex hull volume, and species and functional group richness) that emphasize different attributes of functional diversity, plus 11 extensions of these existing metrics that incorporate heterogeneous species abundances and trait variation. We assess the relationships among these metrics and compare their performances for predicting three key ecosystem functions (above- and belowground biomass and light capture) within a long-term grassland biodiversity experiment. Many metrics were highly correlated, although unique information was captured in FEve, FDiv, and dendrogram-based measures (FD) that were adjusted by abundance. FD adjusted by abundance outperformed all other metrics in predicting both above- and belowground biomass, although several others also performed well (e.g. Rao’s Q, FDis, FDiv). More generally, trait-based richness metrics and hybrid metrics incorporating multiple diversity attributes outperformed evenness metrics and single-attribute metrics, results that were not changed when combinations of metrics were explored. For light capture, species richness alone was the best predictor, suggesting that traits for canopy architecture would be necessary to improve predictions. Our study provides a comprehensive test linking different attributes of functional diversity with ecosystem function for a grassland system.
To evaluate the feasibility of longitudinal assessment and the psychometric properties of both established and new outcome measures used in clinical trials of patients with dementia in a cohort of Spanish-speaking elders in the United States.
This is a prospectively collected multicenter study comparing patients with Alzheimer disease (AD) (N = 77) and elderly controls (N = 17) who are primary Spanish speakers. Spanish-speaking individuals with AD (SSI AD) were selected to represent predefined categories of impairment as determined by a Mini-Mental State Examination score. Controls were selected to approximately match by age and education (SSI C). Subjects were administered a series of Spanish translations of established outcome measures (Mini-Mental State Examination, Clinical Dementia Rating, Geriatric Dementia Scale), and Functional Assessment Staging (FAST)] and new outcome measures developed for United States in clinical trials to assess cognition, function, behavioral disturbance, and clinical global change. Half of the subjects were assessed at 1 and 2 months to evaluate reliability; all subjects were assessed at 6 and 12 months. Comparisons were made between patients and controls and between the Spanish-speaking cohort and a similar English-speaking cohort.
The 12-month completion rate was 77%, with a trend toward greater impairment in those with full retention. Both established and new measures demonstrated good internal consistency and test-retest reliability in this cohort. All but one measure of cognition demonstrated excellent discriminability between AD subjects and controls. The SSI AD cohort declined significantly on measures of cognition, function, and clinical global change over the 12-month assessment period. The SSI AD and English AD (ESI AD) cohorts declined equivalently on the most common outcomes in clinical trials of AD (delayed recall, clinical global change). Likewise, the most common behavioral changes were also similar in the ESI and SSI groups. However, the annual change was lower in SSI AD than in the ESI AD on several other measures of cognition and function.
These results support the recruitment of Spanish-speaking patients and the use of Spanish language translations for use in the clinical trials for AD.
Alzheimer disease; Spanish language assessment; outcome measures; clinical trials
To assess regions and patterns of brain atrophy in patients with Parkinson disease (PD) with normal cognition (PD-NC), mild cognitive impairment (PD-MCI), and dementia-level cognitive deficits (PDD).
Images were quantified using a region-of-interest approach and voxel-based morphometry analysis. We used a high-dimensional pattern classification approach to delineate brain regions that collectively formed the Spatial Pattern of Abnormalities for Recognition of PDD.
The Parkinson’s Disease and Movement Disorders Center at the University of Pennsylvania.
Eighty-four PD patients (61 PD-NC, 12 PD-MCI, and 11 PDD) and 23 healthy control subjects (HCs) underwent magnetic resonance imaging of the brain.
The PD-NC patients did not demonstrate significant brain atrophy compared with HCs. Compared with PD-NC patients, PD-MCI patients had hippocampal atrophy (β=−0.37; P=.001), and PDD patients demonstrated hippocampal (β=−0.32; P=.004) and additional medial temporal lobe atrophy (β=−0.36; P=.003). The PD-MCI patients had a different pattern of atrophy compared with PD-NC patients (P=.04) and a similar pattern to that of PDD patients (P=.81), characterized by hippocampal, prefrontal cortex gray and white matter, occipital lobe gray and white matter, and parietal lobe white matter atrophy. In nondemented PD patients, there was a correlation between memory-encoding performance and hippocampal volume.
Hippocampal atrophy is a biomarker of initial cognitive decline in PD, including impaired memory encoding and storage, suggesting heterogeneity in the neural substrate of memory impairment. Use of a pattern classification approach may allow identification of diffuse regions of cortical gray and white matter atrophy early in the course of cognitive decline.
Predator-prey interactions are vital determinants in the natural selection of behavioral traits. However, we have few insights into both the neural mechanisms and the selective advantage of specific behavioral traits. Gentle touch to the anterior half of the body of Caenorhabditis elegans elicits an escape response in which the animal quickly reverses and suppresses exploratory head movements . Even though the C. elegans touch response has provided one of the rare examples of how neural networks translate sensory input to a coordinated motor output , the ecological significance of the escape response is unclear. We investigate predator-prey relationships between C. elegans and predacious fungi that catch nematodes using constricting rings as trapping devices. We show that the constricting rings of Drechslerella doedycoides catch early larval stages with a diameter similar to the trap opening. There is a delay between the ring entry and ring closure, which allows the animal to withdraw from the trap before getting caught. Mutants that fail to suppress head movements in response to touch are caught more efficiently than the wild type in constricting fungal rings. Direct competition experiments show that the suppression of head movements in response to touch is an ecologically relevant behavior that allows the C. elegans to smoothly retract from a fungal noose and evade capture. These results suggest that selective pressures imposed by predacious fungi have shaped the evolution of C. elegans escape behavior.
Most people with Parkinson's disease (PD) eventually develop cognitive impairment (CI). However, neither the timing of onset nor the severity of cognitive symptoms can be accurately predicted. We sought plasma-based biomarkers for CI in PD.
A discovery cohort of 70 PD patients was recruited. Cognitive status was evaluated with the Mattis Dementia Rating Scale-2 (DRS) at baseline and on annual follow-up visits, and baseline plasma levels of 102 proteins were determined with a bead-based immunoassay. Using linear regression, we identified biomarkers of CI in PD, i.e. proteins whose levels correlated with cognitive performance at baseline and/or cognitive decline at follow-up. We then replicated the association between cognitive performance and levels of the top biomarker, using a different technical platform, with a separate cohort of 113 PD patients.
Eleven proteins exhibited plasma levels correlating with baseline cognitive performance in the discovery cohort. The best candidate was epidermal growth factor (EGF, p<0.001); many of the other 10 analytes co-varied with EGF across samples. Low levels of EGF not only correlated with poor cognitive test scores at baseline, but also predicted an eightfold greater risk of cognitive decline to dementia-range DRS scores at follow-up for those with intact baseline cognition. A weaker, but still significant, relationship between plasma EGF levels and cognitive performance was found in an independent replication cohort of 113 PD patients.
Our data suggest that plasma EGF may be a biomarker for progression to CI in PD.
Epidermal growth factor; EGF; Parkinson's Disease; Parkinson's Disease with Dementia; Biomarker; Plasma
To evaluate the cause of diagnostic errors in the visual interpretation of positron emission tomography scans with 18F-fluorodeoxyglucose (FDG-PET) in patients with frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD).
Twelve trained raters unaware of clinical and autopsy information independently reviewed FDG-PET scans and provided their diagnostic impression and confidence of either FTLD or AD. Six of these raters also recorded whether metabolism appeared normal or abnormal in 5 predefined brain regions in each hemisphere – frontal cortex, anterior cingulate cortex, anterior temporal cortex, temporoparietal cortex and posterior cingulate cortex. Results were compared to neuropathological diagnoses.
Academic medical centers
45 patients with pathologically confirmed FTLD (n=14) or AD (n=31)
Raters had a high degree of diagnostic accuracy in the interpretation of FDG-PET scans; however, raters consistently found some scans more difficult to interpret than others. Unanimity of diagnosis among the raters was more frequent in patients with AD (27/31, 87%) than in patients with FTLD (7/14, 50%) (p = 0.02). Disagreements in interpretation of scans in patients with FTLD largely occurred when there was temporoparietal hypometabolism, which was present in 7 of the 14 FTLD scans and 6 of the 7 lacking unanimity. Hypometabolism of anterior cingulate and anterior temporal regions had higher specificities and positive likelihood ratios for FTLD than temporoparietal hypometabolism had for AD.
Temporoparietal hypometabolism in FTLD is common and may cause inaccurate interpretation of FDG-PET scans. An interpretation paradigm that focuses on the absence of hypometabolism in regions typically affected in AD before considering FTLD is likely to misclassify a significant portion of FTLD scans. Anterior cingulate and/or anterior temporal hypometabolism indicates a high likelihood of FTLD, even when temporoparietal hypometabolism is present. Ultimately, the accurate interpretation of FDG-PET scans in patients with dementia cannot rest on the presence or absence of a single region of hypometabolism, but must take into account the relative hypometabolism of all brain regions.
Disease-modifying therapies for Alzheimer’s disease (AD) would be most beneficial if applied during the ‘preclinical’ stage (pathology present with cognition intact) before significant neuronal loss occurs. Therefore, biomarkers that can detect AD pathology in its early stages and predict dementia onset and progression will be invaluable for patient care and efficient clinical trial design.
2D–difference gel electrophoresis and liquid chromatography tandem mass spectrometry were used to measure AD-associated changes in cerebrospinal fluid (CSF). Concentrations of CSF YKL-40 were further evaluated by enzyme-linked immunosorbent assay in the discovery cohort (N=47), an independent sample set (N=292) with paired plasma samples (N=237), frontotemporal lobar degeneration (N=9), and progressive supranuclear palsy (PSP, N=6). Human AD brain was studied immunohistochemically to identify potential source(s) of YKL-40.
In the discovery and validation cohorts, mean CSF YKL-40 was higher in very mild and mild AD-type dementia (Clinical Dementia Rating [CDR] 0.5 and 1) vs. controls (CDR 0) and PSP. Importantly, CSF YKL-40/Aβ42 ratio predicted risk of developing cognitive impairment (CDR 0 to CDR>0 conversion) as well as the best CSF biomarkers identified to date, tau/Aβ42 and p-tau181/Aβ42. Mean plasma YKL-40 was higher in CDR 0.5 and 1 vs. CDR 0 groups, and correlated with CSF levels. YKL-40 immunoreactivity was observed within astrocytes near a subset of amyloid plaques, implicating YKL-40 in the neuroinflammatory response to Aβ deposition.
These data demonstrate that YKL-40, a putative indicator of neuroinflammation, is elevated in AD, and that, together with Aβ42, has potential prognostic utility as a biomarker for preclinical AD.
YKL-40; Alzheimer’s disease; biomarkers; cerebrospinal fluid; chitinase-3 like-1; inflammation
Quantitation of isoprostanes such as 8-iso-PGF2α and 8,12-iso-iPF2α-VI in biological fluids has been proposed as a reliable test of oxidant stress and inflammation in a variety of disorders. This paper presents a liquid chromatography method with tandem mass spectrometry detection for the simultaneous analysis of these two isoprostanes in human CSF and brain tissue samples. An API 5000 triple quadrupole instrument (AB Sciex, Foster City, CA, USA) with an APCI ion source was used in this study. Aliquots of CSF samples (0.25mL) were treated with a methanol:zinc sulfate mixture followed by on-line cleanup on an extraction column (Validated-C18) with 0.1% formic acid. The brain tissue samples were homogenized and lipids were extracted using Folch solution. Solid phase extraction columns (C18) were used for the purification of the brain isoprostane fraction. Chromatographic separation was achieved using an analytical column (Synergi C18 HydroRP) with 0.1% formic acid in water and a mixture of methanol:acetonitrile under isocratic conditions. The mass spectrometer was operated in the MRM scan and negative ion mode. The quadrupoles were set to detect the molecular ions [M-H]− and high mass fragments of isoprostanes: m/z 353→193 amu (8-iso-PGF2α) and m/z 353→115 amu (8,12-iso-iPF2α-VI) and their deuterated internal standards: m/z 357→197 amu (8-iso-PGF2α-d4) and m/z 364 → 115 amu (8,12-iso-iPF2α -VI-d11). The lower limit of quantification was 2.5 pg/mL for 8-iso-PGF2α and 5.0 pg/mL for 8,12-iso-PF2α-VI for the CSF method and 10.0 pg/0.1 g of tissue and 30.0 pg/0.1 g of tissue for 8-iso-PGF2α and 8,12-iso-iPF2α -VI, respectively, for the brain tissue method. No ion suppression or enhancement of the detection of 8-isoPGF2α, 8,12-isoPF2α-VI or both internal standards was found.
8-iso-PGF2α; 8, 12-iso-iPF2α-VI; HPLC-MS/MS; on-line cleanup; CSF; brain tissue samples
Florbetapir F 18 PET can image amyloid-β (Aβ) aggregates in the brains of living subjects. We prospectively evaluated the prognostic utility of detecting Aβ pathology using florbetapir PET in subjects at risk for progressive cognitive decline.
A total of 151 subjects who previously participated in a multicenter florbetapir PET imaging study were recruited for longitudinal assessment. Subjects included 51 with recently diagnosed mild cognitive impairment (MCI), 69 cognitively normal controls (CN), and 31 with clinically diagnosed Alzheimer disease dementia (AD). PET images were visually scored as positive (Aβ+) or negative (Aβ−) for pathologic levels of β-amyloid aggregation, blind to diagnostic classification. Cerebral to cerebellar standardized uptake value ratios (SUVr) were determined from the baseline PET images. Subjects were followed for 18 months to evaluate changes in cognition and diagnostic status. Analysis of covariance and correlation analyses were conducted to evaluate the association between baseline PET amyloid status and subsequent cognitive decline.
In both MCI and CN, baseline Aβ+ scans were associated with greater clinical worsening on the Alzheimer's Disease Assessment Scale–Cognitive subscale (ADAS-Cog (p < 0.01) and Clinical Dementia Rating–sum of boxes (CDR-SB) (p < 0.02). In MCI Aβ+ scans were also associated with greater decline in memory, Digit Symbol Substitution (DSS), and Mini-Mental State Examination (MMSE) (p < 0.05). In MCI, higher baseline SUVr similarly correlated with greater subsequent decline on the ADAS-Cog (p < 0.01), CDR-SB (p < 0.03), a memory measure, DSS, and MMSE (p < 0.05). Aβ+ MCI tended to convert to AD dementia at a higher rate than Aβ− subjects (p < 0.10).
Florbetapir PET may help identify individuals at increased risk for progressive cognitive decline.
Here we review progress by the Penn Biomarker Core in the Alzheimer's disease Neuroimaging Initiative (ADNI) towards developing a pathological cerebrospinal fluid (CSF) and plasma biomarker signature for mild Alzheimer's disease (AD) as well as a biomarker profile that predicts conversion of mild cognitive impairment (MCI) and/or normal control (NC) subjects to AD. The Penn Biomarker Core also collaborated with other ADNI Cores to integrate data across ADNI to temporally order changes in clinical measures, imaging data and chemical biomarkers that serve as mileposts and predictors of the conversion of NC to MCI as well as MCI to AD, and the progression of AD.
Initial CSF studies by the ADNI Biomarker Core revealed a pathological CSF biomarker signature of AD defined by the combination of Aβ1-42 and total tau (T-tau) that effectively delineates mild AD in the large multisite prospective clinical investigation conducted in ADNI. This signature appears to predict conversion from MCI to AD. Data fusion efforts across ADNI Cores generated a model for the temporal ordering of AD biomarkers which suggests that Aβ amyloid biomarkers become abnormal first, followed by changes in neurodegenerative biomarkers (CSF tau, FDG-PET, MRI) and the onset of clinical symptoms. The timing of these changes varies in individual patients due to genetic and environmental factors that increase or decrease an individual's resilience in response to progressive accumulations of AD pathologies. Further studies in ADNI will refine this model and render the biomarkers studied in ADNI more applicable to routine diagnosis and to clinical trials of disease modifying therapies.
Alzheimer's disease; cerebrospinal fluid; plasma; biomarkers; mild cognitive impairment
To compare presentation of Alzheimer disease (AD) at the time of initial evaluation at a university specialty clinic across three ethnoracial groups in order to understand similarities and differences in the demographic, clinical, cognitive, psychiatric, and biologic features.
A total of 1,341 self-identified African American, Latino (primarily of Caribbean origin), and white non-Hispanic (“WNH”) subjects were recruited from primary care sites or by referral by primary care physicians.
Demographic variables and age of onset of AD, as well as cognitive, functional, and mood impairments at the time of initial presentation and frequencies of apolipoprotein E genotypes, were compared across groups.
Differences among ethnoracial groups were found for nearly all variables of interest. In particular, the largely immigrant Puerto Rican Latino group had an earlier age of onset of AD, more cognitive impairment, and greater severity of cognitive impairment at the time of initial evaluation in the setting of low average education and socioeconomic status. There was more depression in the Latinos compared with African Americans and WNHs. Greater severity of symptoms was not accounted for by a difference in lag time between onset of symptoms and initial evaluation. The apolipoprotein E-4 genotype was not associated with AD in the Latino cohort.
Minority groups in Philadelphia, especially Latinos, exhibit a more severe profile of AD at the time of presentation than WNHs. Important potential confounds need to be considered and future research comparing immigrant and nonimmigrant Latino groups will be necessary to elucidate the highly significant differences reported.
Alzheimer disease; APOE; dementia; ethnoracial differences
The need of an early and noninvasive diagnosis of AD requires the development of imaging-based techniques. As an alternative, the magnetic resonance image (MRI) relaxation time constant (T1ρ ) was measured in brains of Alzheimer’s disease (AD), mild-cognitive impairment (MCI), and age-matched controls in order to determine whether T1ρ values correlated with the neurological diagnosis.
MRI was performed on AD (n = 48), MCI (n = 45), and age-matched control (n = 41), on a 1.5 Tesla Siemens clinical MRI scanner. T1ρ maps were generated by fitting each pixel’s intensity as a function of the duration of the spin-lock pulse. T1ρ values were calculated from the gray matter (GM) and white matter (WM) of medial temporal lobe (MTL).
GM and WM T1ρ values were 87.5 ± 1.2 ms and 80.5 ± 1.4 ms, respectively, in controls, 90.9 ± 1.3 ms and 84.1 ± 1.7 ms in MCI, and 91.9 ±.8 ms and 88.3 ± 1.3 ms in AD cohorts. Compared to control, AD patients showed 9% increased WM T1ρ and 5% increased GM T1ρ. Compared to control, MCI individuals showed 4% increased T1ρ both in WM and GM. A 5% increased T1ρ was found in WM of AD over MCI.
The increased T1ρ in WM and GM of MTL in AD may be associated with the pathological changes that are not evident on conventional MRI.
Alzheimer’s disease; medial temporal lobe; MRI; T1ρ
Ante-mortem diagnosis of neurodegenerative disorders based on clinical features alone is associated with variable sensitivity and specificity, and biomarkers can potentially improve the accuracy of clinical diagnosis. In patients suspected of having Alzheimer’s disease (AD), alterations in cerebrospinal fluid (CSF) biomarkers that reflect the neuropathologic changes of AD strongly support the diagnosis, although there is a trade-off between sensitivity and specificity due to similar changes in cognitively healthy subjects. Here we review the current approaches in using CSF AD biomarkers (total tau, p-tau181, and Aβ42) to predict the presence of AD pathology, and our recent work using multi-analyte profiling to derive novel biomarkers for biofluid-based AD diagnosis. We also review our use of the multi-analyte profiling strategy to identify novel biomarkers that can distinguish between subtypes of frontotemporal lobar degeneration, and those at risk of developing cognitive impairment in Parkinson’s disease. Multi-analyte profiling is a powerful tool for biomarker discovery in complex neurodegenerative disorders, and analytes associated with one or more diseases may shed light on relevant biological pathways and potential targets for intervention.
Biomarker; diagnosis; Alzheimer’s disease; frontotemporal dementia; Lewy bodie; tau; tauopathy; TDP-43
To measure clinically relevant change in Alzheimer's disease (AD) using a family member completed dementia severity rating scale (DSRS) questionnaire.
Measuring rate of change provides important clinical information. Most neuropsychological scores change nonlinearly, complicating their use as a predictor of change throughout the illness.
DSRS and Mini Mental State (MMS) scores were prospectively collected on 702 patients with AD from first evaluation until they became too impaired to return to clinic.
DSRS score increased an average of 4.48 points per year (95% CI 4.14 - 4.82) throughout the entire range of severity. In contrast, the MMS declined an average of 2.15 points per year (95% CI 1.85-2.46) during the first two years, accelerated to 3.83 points per year (95% CI 3.28-4.38) during the subsequent three years and then slowed to an annual decline of 1.63 points during the last two years (95% CI 0.21-3.05). A younger age of symptom onset was associated with an increased rate of DSRS change (p=0.03).
The DSRS provides a clinical measure of functional impairment in AD that increases about 4.48 points per year from the earliest symptomatic stage until patients become too severely impaired to return to clinic.
Dementia severity rating scale; Alzheimer's disease; Rate of decline
To determine the impact of cortical Alzheimer disease pathology on shunt responsiveness in individuals treated for idiopathic normal pressure hydrocephalus (iNPH), 37 patients clinically diagnosed with iNPH participated in a prospective study in which performance on neurologic, psychometric, and gait measures before and 4 months after shunting was correlated with amyloid β plaques, neuritic plaques, and neurofibrillary tangles observed in cortical biopsies obtained during shunt insertion. No complications resulted from biopsy acquisition. Moderate to severe pathology was associated with worse baseline cognitive performance and diminished postoperative improvement on NPH symptom severity scales, gait measures, and cognitive instruments compared to patients lacking pathology.
Mutation in the progranulin gene (GRN) can cause frontotemporal dementia (FTD). However, it is unclear whether some rare FTD-related GRN variants are pathogenic and whether neurodegenerative disorders other than FTD can also be caused by GRN mutations.
To delineate the range of clinical presentations associated with GRN mutations and to define pathogenic candidacy of rare GRN variants.
Clinical and neuropathology dementia research studies at 8 academic centers.
Four hundred thirty-four patients with FTD, including primary progressive aphasia, semantic dementia, FTD/amyotrophic lateral sclerosis (ALS), FTD/motor neuron disease, corticobasal syndrome/corticobasal degeneration, progressive supranuclear palsy, Pick disease, dementia lacking distinctive histopathology, and pathologically confirmed cases of frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U); and 111 non-FTD cases (controls) in which TDP-43 deposits were a prominent neuropathological feature, including subjects with ALS, Guam ALS and/or parkinsonism dementia complex, Guam dementia, Alzheimer disease, multiple system atrophy, and argyrophilic grain disease.
Main Outcome Measures
Variants detected on sequencing of all 13 GRN exons and at least 80 base pairs of flanking introns, and their pathogenic candidacy determined by in silico and ex vivo splicing assays.
We identified 58 genetic variants that included 26 previously unknown changes. Twenty-four variants appeared to be pathogenic, including 8 novel mutations. The frequency of GRN mutations was 6.9% (30 of 434) of all FTD-spectrum cases, 21.4% (9 of 42) of cases with a pathological diagnosis of FTLD-U, 16.0% (28 of 175) of FTD-spectrum cases with a family history of a similar neurodegenerative disease, and 56.2% (9 of 16) of cases of FTLD-U with a family history.
Pathogenic mutations were found only in FTD-spectrum cases and not in other related neurodegenerative diseases. Haploinsufficiency of GRN is the predominant mechanism leading to FTD.
The Alzheimer's Disease Cooperative Study - Clinical Global Impression of Change (ADCS-CGIC) was modified for use in mild cognitive impairment (MCI) trials and tested in the ADCS MCI randomized clinical trial of donepezil, vitamin E and placebo. We assessed feasibility for its use by determining whether or not: (1) it distinguished a medication effect at 6- and 12- months, (2) baseline demographic or clinical characteristics predicted change, (3) there was an association between MCI-CGIC and change in other clinical measures in order to evaluate external or concurrent validity.
We used a generalized estimating equations approach for ordinal outcome data to test the effects of treatment, baseline characteristics and change in clinical measures on the MCI-CGIC over 12 months, and ordinal logistic regression to assess the association between MCI-CGIC and change in clinical measures at 6 months and 12 months.
On the MCI-CGIC overall, 12.9% and 10.6% were rated as having improved, and 31.6% and 39.8% as having worsened over 6- and 12-months, respectively. The MCI-CGIC did not distinguish the donepezil or vitamin E groups from placebo at 6 and 12 months treatment. Variables at screening or baseline that were associated with worse CGIC scores over 6 and 12 months included white race, greater years of education, worse depression, dementia severity rating, cognitive, and daily activities scores, and lower memory domain scores on a neuropsychological battery. Rate of worsening on the MCI-CGIC over 12 months was associated with change on the AD Assessment Scale-cognitive (ADAS-cog) and on executive function. Worsening at 6 months and 12 months, separately, were associated with the corresponding change in ADAS-cog, ADL, BDI, MMSE, CDR-sb, memory, and executive function.
Change detected by the MCI-CGIC was associated with baseline clinical severity and with change in clinical ratings over 6 and 12 months, supporting the validity of a CGIC approach in MCI. The effect size of the donepezil-placebo difference was similar to that of other outcomes at 12 months. About 40% of MCI patients were judged worse and about 11% improved, consistent with clinical experience and other ratings.
Mild cognitive impairment; Alzheimer's disease; dementia; global impression of change; rating scales; donepezil; vitamin E; clinical trials
Alzheimer’s disease (AD) patients have been reported to have shorter telomeres in peripheral blood leukocytes (PBLs) than age-matched control subjects. However, it is unclear if PBL telomere length reflects brain telomere length, which might play a more direct role in AD pathogenesis. We examined the correlation between PBL and cerebellum telomere length in AD patients, and compared telomere lengths in cerebella from individuals with AD versus age-matched control subjects.
Mean telomere lengths were measured using quantitative telomere polymerase chain reaction of genomic DNA prepared from matched PBL and cerebellum samples from 29 individuals with pathologically confirmed sporadic AD. Telomere length was also measured in cerebellum samples of 30 AD patients versus 22 unaffected age-matched control subjects.
The PBL and cerebellum telomere lengths were directly correlated in individuals with AD (r = 0.42, P = 0.023). Nonetheless, cerebellum telomere lengths were not significantly different in AD patients and age-matched control subjects.
Reduced PBL telomere length in AD might not reflect reduced telomere length in bulk brain tissue, but may be a marker of changes in a subset of brain tissues or other tissues that affect the pathogenesis of AD.
Alzheimer’s disease; Telomere; Cerebellum; Aging
To evaluate the T1rho (T1ρ) MRI relaxation time in hippocampus in the brain of Alzheimer’s disease (AD), mild cognitive impairment (MCI), and control, and to determine whether the T1ρ shows any significant difference between these cohorts.
Materials and Methods
With informed consent, AD (n = 49), MCI (n = 48), and age-matched control (n = 31) underwent T1ρ MRI on a Siemens 1.5T Scanner. T1ρ values were automatically calculated from the left and right hippocampus region using in-house developed software. Bonferroni post-hoc multiple comparisons was performed to compare the T1ρ value among the different cohorts.
Significantly higher T1ρ values were observed both in AD (P = 0.000) and MCI (P = 0.037) cohorts compared to control; also, the T1ρ in AD was significantly high over (P = 0.032) MCI. Hippocampus T1ρ was 13% greater in the AD patients than control, while in MCI it was 7% greater than control. Hippocampus T1ρ in AD patients was 6% greater than MCI.
Higher hippocampus T1ρ values in the AD patients might be associated with the increased plaques burden. A follow-up study would help to determine the efficacy of T1ρ values as a predictor of developing AD in the control and MCI individuals.
Alzheimer’s disease; hippocampus; MRI; T1rho