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Biomedical subjects

Steven T DeKosky

Publications and source records attributed to Steven T DeKosky.

At least 19 recordsLinked to original sources
PubMed2011

Common variants at MS4A4/MS4A6E, CD2AP, CD33 and EPHA1 are associated with late-onset Alzheimer's disease.

The Alzheimer Disease Genetics Consortium (ADGC) performed a genome-wide association study of late-onset Alzheimer disease using a three-stage design consisting of a discovery stage (stage 1) and two replication stages (stages 2 and 3). Both joint analysis and meta-analysis approaches were used. We obtained genome-wide significant results at MS4A4A (rs4938933; stages 1 and 2, meta-analysis P (P(M)) = 1.7 × 10(-9), joint analysis P (P(J)) = 1.7 × 10(-9); stages 1, 2 and 3, P(M) = 8.2 × 10(-12)), CD2AP (rs9349407; stages 1, 2 and 3, P(M) = 8.6 × 10(-9)), EPHA1 (rs11767557; stages 1, 2 and 3, P(M) = 6.0 × 10(-10)) and CD33 (rs3865444; stages 1, 2 and 3, P(M) = 1.6 × 10(-9)). We also replicated previous associations at CR1 (rs6701713; P(M) = 4.6 × 10(-10), P(J) = 5.2 × 10(-11)), CLU (rs1532278; P(M) = 8.3 × 10(-8), P(J) = 1.9 × 10(-8)), BIN1 (rs7561528; P(M) = 4.0 × 10(-14), P(J) = 5.2 × 10(-14)) and PICALM (rs561655; P(M) = 7.0 × 10(-11), P(J) = 1.0 × 10(-10)), but not at EXOC3L2, to late-onset Alzheimer's disease susceptibility.

Adaptor Proteins, Signal Transducing↗
PubMed2008

Frequent amyloid deposition without significant cognitive impairment among the elderly.

OBJECTIVE: To characterize the prevalence of amyloid deposition in a clinically unimpaired elderly population, as assessed by Pittsburgh Compound B (PiB) positron emission tomography (PET) imaging, and its relationship to cognitive function, measured with a battery of neuropsychological tests. DESIGN: Subjects underwent cognitive testing and PiB PET imaging (15 mCi for 90 minutes with an ECAT HR+ scanner). Logan graphical analysis was applied to estimate regional PiB retention distribution volume, normalized to a cerebellar reference region volume, to yield distribution volume ratios (DVRs). SETTING: University medical center. PARTICIPANTS: From a community-based sample of volunteers, 43 participants aged 65 to 88 years who did not meet diagnostic criteria for Alzheimer disease or mild cognitive impairment were included. MAIN OUTCOME MEASURES: Regional PiB retention and cognitive test performance. RESULTS: Of 43 clinically unimpaired elderly persons imaged, 9 (21%) showed evidence of early amyloid deposition in at least 1 brain area using an objectively determined DVR cutoff. Demographic characteristics did not differ significantly between amyloid-positive and amyloid-negative participants, and neurocognitive performance was not significantly worse among amyloid-positive compared with amyloid-negative participants. CONCLUSIONS: Amyloid deposition can be identified among cognitively normal elderly persons during life, and the prevalence of asymptomatic amyloid deposition may be similar to that of symptomatic amyloid deposition. In this group of participants without clinically significant impairment, amyloid deposition was not associated with worse cognitive function, suggesting that an elderly person with a significant amyloid burden can remain cognitively normal. However, this finding is based on relatively small numbers and needs to be replicated in larger cohorts. Longitudinal follow-up of these subjects will be required to support the potential of PiB imaging to identify preclinical Alzheimer disease, or, alternatively, to show that amyloid deposition is not sufficient to cause Alzheimer disease within some specified period.

Aged↗
PubMed2007

Association of tagSNPs in the urokinase-plasminogen activator (PLAU) gene with Alzheimer's disease and associated quantitative traits.

The gene coding for urokinase-plasminogen activator (PLAU) is a strong biological and positional candidate gene for Alzheimer's disease (AD). Previously some studies have examined the role of common variation in the PLAU gene with AD risk but the results have been inconsistent and this inconsistency could have been due to the use of relatively small sample sizes. In this study we evaluated the distribution of four tagSNPs (rs2227562 in intron 5, rs2227564 in exon 6, rs2227571 in intron 9, and rs4065 in 3'UTR) in the PLAU gene in a large case-control study consisting of up to 1,000 AD patients and 697 white control subjects. We examined the role of these tagSNPs with AD risk and quantitative traits of AD, including age-at-onset (AAO), disease duration, and mini-mental state examination (MMSE) scores. The 3'UTR SNP revealed modest significant association with risk (OR = 0.71, 95% CI: 0.53-0.95; P = 0.02), AAO (P = 0.036) and disease duration (P = 0.04) of AD. In addition, the intron 9 SNP also revealed a significant association with AAO (P = 0.01) and disease duration (P = 0.006). Our data on a large number of AD cases and controls suggest that genetic variation in PLAU may affect the risk and AAO of AD.

3' Untranslated Regions↗
PubMed2006

Maintaining adherence and retention in dementia prevention trials.

Incidence and prevalence of Alzheimer Disease (AD) will rise in a accelerating fashion through the middle of the 21st century. Increased understanding of the pathological cascades in AD, and the knowledge that the initial brain changes begin years prior to clinical manifestations, have led to initiation of trials to prevent AD. With many of the designs being used or contemplated, prevention trials will involve repeated cognitive and functional assessments over years, require cooperation and collaboration of both the subject and a partner or proxy, and represent a substantial time and resource investment by the research team. Compliance with the study regimen and adherence to the protocol are thus major foci for study efficiency and success. In this section methods by which compliance and adherence can be optimized are discussed. Research on the effectiveness of these and other evolving methods will be of help in assuring success of such large scale studies in the future.

Alzheimer Disease↗
PubMed2006

Primary prevention trials in Alzheimer disease.

Many new treatments under development for Alzheimer disease (AD) will be disease-modifying rather than symptomatic. Clinical evaluation of these treatments will require primary and secondary prevention trials. We describe some of the methodologic challenges in designing primary prevention trials for AD and illustrate these with examples from the ADAPT (Alzheimer Disease Anti-Inflammatory Prevention Trial) Study and GEM (Ginkgo in Evaluation of Memory) Study. Primary prevention trials for AD present many design challenges. In most situations, secondary prevention trials provide the most feasible first step toward primary prevention.

Alzheimer Disease↗
PubMed2006

Lack of association of two chromosome 10q24 SNPs with Alzheimer's disease.

Several groups have reported evidence of linkage on chromosome 10 to late-onset Alzheimer's disease (LOAD). In a recent scan of single nucleotide polymorphisms (SNPs) on chromosome 10, significant associations between the rs498055 and rs4417206 SNPs and risk of LOAD were observed. We examined the association of these two SNPs with LOAD risk in a large Caucasian American cohort comprising about 2000 cases and controls. Neither SNP revealed significant association with LOAD risk or age-at-onset.

Alzheimer Disease↗
PubMed2006

Lack of association of 5 SNPs in the vicinity of the insulin-degrading enzyme (IDE) gene with late-onset Alzheimer's disease.

Insulin-degrading enzyme (IDE) is a strong biological and positional candidate gene for Alzheimer's disease (AD). Previously some studies have examined the role of common variation in the IDE gene with AD risk but the results have been inconsistent. In this study we examined the role of 5 SNPs that define a linkage disequilibrium (LD) block spanning 276kb around IDE. Our sample comprised up to 1012 late-onset AD (LOAD) cases and 771 older white controls. In addition, we also examined the association of these SNPs with quantitative measures of AD progression, namely age-at-onset (AAO), disease duration and Mini-Mental State Examination (MMSE) score. None of the SNPs examined in this fairly large case-control sample revealed significant association with AD risk. These SNPs also showed no significant association with AD quantitative traits.

Aged↗
PubMed2006

Evaluation of voxel-based methods for the statistical analysis of PIB PET amyloid imaging studies in Alzheimer's disease.

Deposition of amyloid plaques is believed to be a central event in the development of Alzheimer's disease (AD). The present study was undertaken to evaluate statistical methods for the assessment of group differences in retention of an amyloid imaging agent, PIB, throughout the brain and to compare these results to FDG studies of glucose metabolism performed in the same subjects on the same day. PET studies were performed in 10 mild to moderate AD and 11 control subjects. Parametric images of PIB retention (over 90 min post-injection) were generated using the Logan graphical analysis with cerebellar (CER, reference region) data as input. FDG parametric images were created by summing the uptake over 40-60 min post-injection and normalizing that to the CER to give a standardized uptake value ratio. Data were compared using parametric (SPM) and non-parametric (SnPM) statistical methods with familywise error (FWE) and false discovery rate (FDR) corrections. PIB results were consistent with previous regional results as AD subjects showed highly significant retention in frontal, parietal, temporal, and posterior cingulate cortices (FDR-corrected p<1.4e-10). FDG results showed regions of marginally significant decreases in uptake in AD subjects (frontal, parietal, temporal, posterior cingulate cortices: FDR-corrected p<0.1) consistent with previous studies. Relative to FDG, the PIB analyses were of greater statistical significance and larger spatial extent. Additionally, the PIB analyses retained significance after both FWE and FDR corrections. These results indicate that voxel-based methods will be useful for future larger longitudinal studies of amyloid deposition that could improve AD diagnosis and anti-amyloid therapy assessment.

Aged↗
PubMed2006

Recruitment of the elderly into a pharmacologic prevention trial: the Ginkgo Evaluation of Memory Study experience.

The difficulty involved in recruiting healthy older adults into clinical trials, especially those involving pharmacologic agents, is an important issue in research. The Ginkgo Evaluation of Memory (GEM) Study, a double-blind, placebo-controlled randomized clinical trial evaluating Ginkgo biloba to prevent dementia, successfully recruited 3072 participants age 75 years and older at four U.S. sites from September 2000 through June 2002. Using targeted mailing lists, an estimated 243,400 study brochures were mailed out to potential participants. Subsequent attempts were made to reach 14,603 households by telephone, from which 12,186 (83.4%) successful contacts were made. Overall, telephone or in-person evaluations identified 2149 (17.6%) ineligible persons for cognitive (20.6%), medical (49.4%), or other (30.0%) reasons. A total of 6944 (57.0%) refused participation resulting in 3072 enrolled into the study, a recruitment rate of 25.2% based on telephone contacts made or 1.3% of all mailed brochures. Recruitment rates were stable over the 21-month enrollment period but were higher for the two urban centers than the two rural ones. Recruitment was dependent most on mailing lists available, density of older adults in the catchment areas, and Institutional Review Board restrictions. Men and persons under age 85 were more likely to enroll. Primary reason for refusals involved lack of interest (48.4%) or self-perceived poor health (16.2%). Over 9% were unwilling to give up current Ginkgo supplementation or would not accept assignment to placebo. An additional 7% did not want another medication and almost 4% had care-giving responsibilities which prevented involvement. Mass mailings were the most successful approach for recruitment at all four sites and the method through which the vast majority of interviewees had learned about the study. Information on the experience of the GEM Study recruitment may be helpful to other clinical trials attempting to randomize older adults into prevention trials.

Aged↗
PubMed2006

Gender-specific association of ATP-binding cassette transporter 1 (ABCA1) polymorphisms with the risk of late-onset Alzheimer's disease.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder caused by a complex interaction of genetic and environmental factors. Increasing evidence highlights a potential role for cholesterol in the pathophysiology of AD. The ABCA1 gene, located in close vicinity to the 9q linkage peaks identified by genome-wide AD linkage studies, plays an important role in cellular cholesterol efflux, and is likely a good candidate gene. However, results from published genetic association studies between ABCA1 and AD are ambiguous. In the present study, we examined the role of two ABCA1 polymorphisms, R219K (rs2230806) and G-17C (rs2740483) in modifying the risk of late-onset AD (LOAD) in a large American white cohort of 992 AD cases and 699 controls. We observed significant gender x R219K interaction (p=0.00008). Female carriers of the 219K allele showed a 1.75-fold increased risk of developing AD compared to non-219K carrier females (95% CI 1.34-2.29; p=0.00004). The overall two-site haplotype distribution was also significant between female AD cases and controls (p=0.017). The risk associated with the R219K polymorphism was independent of the recently reported significant association in the ubiquilin (UBQLN1) gene in this region on chromosome 9q. Our data suggest a gender-specific and APOE and UBQLN1 independent association between the ABCA1/R219K polymorphism and LOAD.

ATP Binding Cassette Transporter 1↗
PubMed2006

The Ginkgo Evaluation of Memory (GEM) study: design and baseline data of a randomized trial of Ginkgo biloba extract in prevention of dementia.

The epidemic of late life dementia, prominence of use of alternative medications and supplements, and initiation of efforts to determine how to prevent dementia have led to efforts to conduct studies aimed at prevention of dementia. The GEM (Ginkgo Evaluation of Memory) study was initially designed as a 5-year, randomized double-blind, placebo-controlled trial of Ginkgo biloba, administered in a dose of 120 mg twice per day as EGb761, in the prevention of dementia (and especially Alzheimer's disease) in normal elderly or those with mild cognitive impairment. The study anticipates 8.5 years of participant follow-up. Initial power calculations based on estimates of incidence rates of dementia in the target population (age 75+) led to a 3000-person study, which was successfully recruited at four clinical sites around the United States from September 2000 to June 2002. Primary outcome is incidence of all-cause dementia; secondary outcomes include rate of cognitive and functional decline, the incidence of cardiovascular and cerebrovascular events, and mortality. Following screening to exclude participants with incident dementia at baseline, an extensive neuropsychological assessment was performed and participants were randomly assigned to treatment groups. All participants are required to have a proxy who agreed to provide an independent assessment of the functional and cognitive abilities of the participant. Assessments are repeated every 6 months. Significant decline at any visit, defined by specific changes in cognitive screening scores, leads to a repeat detailed neuropsychological battery, neurological and medical evaluation and MRI scan of the brain. The final diagnosis of dementia is achieved by a consensus panel of experts. Side effects and adverse events are tracked by computer at the central data coordinating center and unblinded data are reviewed by an independent safety monitoring board. Studies such as these are necessary for this and a variety of other potential protective agents to evaluate their effectiveness in preventing or slowing the emergence of dementia in the elderly population.

Aged↗
PubMed2006

Inverse relation between in vivo amyloid imaging load and cerebrospinal fluid Abeta42 in humans.

OBJECTIVES: Amyloid-beta(42) (Abeta(42)) appears central to Alzheimer's disease (AD) pathogenesis and is a major component of amyloid plaques. Mean cerebrospinal fluid (CSF) Abeta(42) is decreased in dementia of the Alzheimer's type. This decrease may reflect plaques acting as an Abeta(42) "sink," hindering transport of soluble Abeta(42) between brain and CSF. We investigated this hypothesis. METHODS: We compared the in vivo brain amyloid load (via positron emission tomography imaging of the amyloid-binding agent, Pittsburgh Compound-B [PIB]) with CSF Abeta(42) and other measures (via enzyme-linked immunosorbent assay) in clinically characterized research subjects. RESULTS: Subjects fell into two nonoverlapping groups: those with positive PIB binding had the lowest CSF Abeta(42) level, and those with negative PIB binding had the highest CSF Abeta(42) level. No relation was observed between PIB binding and CSF Abeta(40), tau, phospho-tau(181), plasma Abeta(40), or plasma Abeta(42). Importantly, PIB binding and CSF Abeta(42) did not consistently correspond with clinical diagnosis; three cognitively normal subjects were PIB-positive with low CSF Abeta(42), suggesting the presence of amyloid in the absence of cognitive impairment (ie, preclinical AD). INTERPRETATION: These observations suggest that brain amyloid deposition results in low CSF Abeta(42), and that amyloid imaging and CSF Abeta(42) may potentially serve as antecedent biomarkers of (preclinical) AD.

Aged↗
PubMed2006

Making sense of mild cognitive impairment: a qualitative exploration of the patient's experience.

PURPOSE: The proposed dementia precursor state of mild cognitive impairment is emerging as a primary target of aging research. Yet, little is known about the subjective experience of living with a diagnosis of mild cognitive impairment. This study examines, from the patient's perspective, the experience of living with and making sense of the diagnosis. DESIGN AND METHODS: We recruited 12 older adults with amnestic or nonamnestic mild cognitive impairment from a university-based memory disorders clinic. We conducted in-home, semistructured interviews in order to elicit rich descriptions of the personal experience of having mild cognitive impairment. We used the qualitative method of grounded theory to analyze narrative data. RESULTS: Understanding and coming to terms with the syndrome, or assigning meaning, constituted a fundamental aspect of living with a diagnosis of mild cognitive impairment. This process comprised interrelated emotional and cognitive dimensions. Participants employed a range of positive, neutral, and negative phrasing in order to depict their emotional reactions to receiving a diagnosis. Cognitive representations of mild cognitive impairment included both prognosis-focused and face-value appraisals. Expectations of normal aging, personal experience with dementia, and concurrent health problems were key contextual factors that provided the backdrop against which participants assigned meaning to a diagnosis of mild cognitive impairment. IMPLICATIONS: Clinicians who disclose diagnoses of mild cognitive impairment need to be mindful of the potential for varying interpretations of the information that is conveyed. Future research needs to include systematic, longitudinal investigations of illness representation and its impact on health behaviors among individuals with mild cognitive impairment.

Aged↗
PubMed2006

Chronic traumatic encephalopathy in a national football league player: part II.

OBJECTIVE: We present the second reported case of autopsy-confirmed chronic traumatic encephalopathy in a retired professional football player, with neuropathological features that differ from those of the first reported case. These differing pathological features underscore the need for further empirical elucidation of the pathoetiology and pathological cascades of long-term neurodegenerative sequelae of professional football. METHODS: A psychological autopsy was performed with the next-of-kin and wife. Medical and hospital records were reviewed. A complete autopsy was accompanied by a comprehensive forensic neuropathological examination. Restriction fragment length polymorphism analysis was performed to determine apolipoprotein-E genotype. RESULTS: Pertinent premortem history included a 14-year span of play in organized football starting from the age of 18 years. The subject was diagnosed with severe major depressive disorder without psychotic features after retirement, attempted suicide multiple times and finally committed suicide 12 years after retirement by ingestion of ethylene glycol. Autopsy revealed cardiomegaly, mild to moderate coronary artery disease, and evidence of acute ethylene glycol overdose. The brain showed no atrophy, a cavum septi pellucidi was present, and the substantia nigra showed mild pallor. The hippocampus and cerebellum were not atrophic. Amyloid plaques, cerebral amyloid angiopathy, and Lewy bodies were completely absent. Sparse to frequent tau-positive neurofibrillary tangles and neuropil threads were present in all regions of the brain. Tufted and thorn astrocytes, as well as astrocytic plaques, were absent. The apolipoprotein-E genotype was E3/E4. CONCLUSION: Our first and second cases both had long careers without multiple recorded concussions. Both manifested Major Depressive Disorder after retirement. Amyloid plaques were present in the first case and completely absent in the second case. Both cases exhibited neurofibrillary tangles, neuropil threads, and coronary atherosclerotic disease. Apolipoprotein-E4 genotypes were different. Reasons for the contrasting features in these two cases are not clear. Further studies are needed to identify and define the neuropathological cascades of chronic traumatic encephalopathy in football players, which may form the basis for prophylaxis and therapeutics.

Brain↗
PubMed2005

Caspase inhibition therapy abolishes brain trauma-induced increases in Abeta peptide: implications for clinical outcome.

The detrimental effects of traumatic brain injury (TBI) on brain tissue integrity involve progressive axonal damage, necrotic cell loss, and both acute and delayed apoptotic neuronal death due to activation of caspases. Post-injury accumulation of amyloid precursor protein (APP) and its toxic metabolite amyloid-beta peptide (Abeta) has been implicated in apoptosis as well as in increasing the risk for developing Alzheimer's disease (AD) after TBI. Activated caspases proteolyze APP and are associated with increased Abeta production after neuronal injury. Conversely, Abeta and related APP/Abeta fragments stimulate caspase activation, creating a potential vicious cycle of secondary injury after TBI. Blockade of caspase activation after brain injury suppresses apoptosis and improves neurological outcome, but it is not known whether such intervention also prevents increases in Abeta levels in vivo. The present study examined the effect of caspase inhibition on post-injury levels of soluble Abeta, APP, activated caspase-3, and caspase-cleaved APP in the hippocampus of nontransgenic mice expressing human Abeta, subjected to controlled cortical injury (CCI). CCI produced brain tissue damage with cell loss and elevated levels of activated caspase-3, Abeta(1-42) and Abeta(1-40), APP, and caspase-cleaved APP fragments in hippocampal neurons and axons. Post-CCI intervention with intracerebroventricular injection of 100 nM Boc-Asp(OMe)-CH(2)F (BAF, a pan-caspase inhibitor) significantly reduced caspase-3 activation and improved histological outcome, suppressed increases in Abeta and caspase-cleaved APP, but showed no significant effect on overall APP levels in the hippocampus after CCI. These data demonstrate that after TBI, caspase inhibition can suppress elevations in Abeta. The extent to which Abeta suppression contributes to improved outcome following inhibition of caspases after TBI is unclear, but such intervention may be a valuable therapeutic strategy for preventing the long-term evolution of Abeta-mediated pathology in TBI patients who are at risk for developing AD later in life.

Amyloid beta-Peptides↗
PubMed2005

Binding of the positron emission tomography tracer Pittsburgh compound-B reflects the amount of amyloid-beta in Alzheimer's disease brain but not in transgenic mouse brain.

During the development of in vivo amyloid imaging agents, an effort was made to use micro-positron emission tomography (PET) imaging in the presenilin-1 (PS1)/amyloid precursor protein (APP) transgenic mouse model of CNS amyloid deposition to screen new compounds and further study Pittsburgh Compound-B (PIB), a PET tracer that has been shown to be retained well in amyloid-containing areas of Alzheimer's disease (AD) brain. Unexpectedly, we saw no significant retention of PIB in this model even at 12 months of age when amyloid deposition in the PS1/APP mouse typically exceeds that seen in AD. This study describes a series of ex vivo and postmortem in vitro studies designed to explain this low retention. Ex vivo brain pharmacokinetic studies confirmed the low in vivo PIB retention observed in micro-PET experiments. In vitro binding studies showed that PS1/APP brain tissue contained less than one high-affinity (K(d) = 1-2 nm) PIB binding site per 1000 molecules of amyloid-beta (Abeta), whereas AD brain contained >500 PIB binding sites per 1000 molecules of Abeta. Synthetic Abeta closely resembled PS1/APP brain in having less than one high-affinity PIB binding site per 1000 molecules of Abeta, although the characteristics of the few high-affinity PIB binding sites found on synthetic Abeta were very similar to those found in AD brain. We hypothesize that differences in the time course of deposition or tissue factors present during deposition lead to differences in secondary structure between Abeta deposited in AD brain and either synthetic Abeta or Abeta deposited in PS1/APP brain.

Alzheimer Disease↗
PubMed2005

Increased phosphorylation of protein kinase B and related substrates after traumatic brain injury in humans and rats.

Activation of protein kinase B (PKB, also known as Akt) by phosphorylation at serine-473 and threonine-308 promotes cell survival in multiple in vitro and in vivo models where neuronal death is seen, including traumatic brain injury (TBI); however, whether PKB is activated in humans after TBI was heretofore unknown. Activated PKB inhibits apoptogenic factors and is involved in the regulation of several transcription factors. Accordingly, we examined phosphorylation of the PKB signaling pathway in humans as well as rats after TBI using phosphospecific antibodies. Increased phosphorylation of PKB and PKB substrates was detected in injured brain from both humans and rats. In humans, increased phosphorylation of the PKB signaling pathway-related proteins Bad and forkhead transcription factor (FKHR) was detected in patients with TBI versus controls. In rats, increased phosphorylation of FKHR, inhibitor of kappaBalpha, and cyclic adenosine monophosphate responsive element binding protein (CREB) was detected after TBI versus controls. The deoxyribonucleic acid-binding activity of CREB was also enhanced after TBI in rats. Increased phosphorylation of PKB and PKB substrates was identified in neurons and other cell types by immunohistochemistry in both humans and rats. These data show increased phosphorylation of PKB, PKB substrates, and related proteins after both experimental and clinical TBI, suggesting either activation of the PKB signaling pathway or reduced phosphatase activity in both species.

Adult↗