Long-lasting memory of jasmonic acid-dependent immunity requires DNA demethylation and ARGONAUTE1

Stress can have long-lasting impacts on plants. Here we report the long-term effects of the stress hormone jasmonic acid (JA) on the defence phenotype, transcriptome and DNA methylome of Arabidopsis. Three weeks after transient JA signalling, 5-week-old plants retained induced resistance (IR) against herbivory but showed increased susceptibility to pathogens. Transcriptome analysis revealed long-term priming and/or upregulation of JA-dependent defence genes but repression of ethylene- and salicylic acid-dependent genes. Long-term JA-IR was associated with shifts in glucosinolate composition and required MYC2/3/4 transcription factors, RNA-directed DNA methylation, the DNA demethylase ROS1 and the small RNA (sRNA)-binding protein AGO1. Although methylome analysis did not reveal consistent changes in DNA methylation near MYC2/3/4-controlled genes, JA-treated plants were specifically enriched with hypomethylated ATREP2 transposable elements (TEs). Epigenomic characterization of mutants and transgenic lines revealed that ATREP2 TEs are regulated by RdDM and ROS1 and produce 21 nt sRNAs that bind to nuclear AGO1. Since ATREP2 TEs are enriched with sequences from IR-related defence genes, our results suggest that AGO1-associated sRNAs from hypomethylated ATREP2 TEs trans-regulate long-lasting memory of JA-dependent immunity.

Straight to test reduces time to investigation and treatment

Straight to test (STT) is a recognised pathway for improving the waiting time for red flag referrals. Electronic patient care records (ECR) provide clinicians with a greater volume of clinical information allowing virtual triage and STT. We aimed to assess if using ECR and STT can reduce delays in diagnosis and treatment. A review of 300 colorectal referrals between 2018-2019 was performed. Patients awaiting an appointment were reviewed electronically, by a single colorectal surgeon and re-triaged STT if appropriate. The delay in time from referral to initial review was removed, creating a second group for statistical comparison to demonstrate time saved if the strategy was adopted at the point of original triage. 91.3% (n= 274) were red flag referrals. 94% (n=282) were sent STT. Patients processed via traditional referral and clinic had a median time to scope of 36 days compared with 22.5 days, p < 0.001 if triaged STT via virtual clinic. Median time to management was 59 days for traditional and 35 days for STT, p < 0.001.

Dietary Allergy and Specific IgE in Ulcerative Colitis

Previous authors have considered that allergy to certain foodstuffs may play an important role in the aetiology of ulcerative colitis, but immunological evidence for dietary allergy in ulcerative colitis is inconclusive. A study is reported of 22 patients with ulcerative colitis, with matched controls, in whom total serum IgE and specific IgE to certain foodstuffs have been estimated by the Phadebas PRIST and RAST (Pharmacia) techniques. Allergens tested were egg-white, milk, wheat, rye, oat, fish (cod) and peanut. There was no significant difference in the total serum IgE levels and the food specific IgE activity between the two groups.

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width-the mediolateral (transverse) distance between successive footfalls-was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk-run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.

Reframing climate change assessments around risk: recommendations for the US National Climate Assessment

Climate change is a risk management challenge for society, with uncertain but potentially severe outcomes affecting natural and human systems, across generations. Managing climate-related risks will be more difficult without a base of knowledge and practice aimed at identifying and evaluating specific risks, and their likelihood and consequences, as well as potential actions to promote resilience in the face of these risks. We suggest three improvements to the process of conducting climate change assessments to better characterize risk and inform risk management actions.

Differential transcriptome expression in human nucleus accumbens as a function of loneliness

Loneliness is associated with impaired mental and physical health. Studies of lonely individuals reported differential expression of inflammatory genes in peripheral leukocytes and diminished activation in brain reward regions such as nucleus accumbens, but could not address gene expression in the human brain. Here, we examined genome-wide RNA expression in post-mortem nucleus accumbens from donors (N=26) with known loneliness measures. Loneliness was associated with 1710 differentially expressed transcripts and genes from 1599 genes (DEGs; false discovery rate P<0.05, fold change ⩾|2|, controlling for confounds) previously associated with behavioral processes, neurological disease, psychological disorders, cancer, organismal injury and skeletal and muscular disorders, as well as networks of upstream RNA regulators. Furthermore, a number of DEGs were associated with Alzheimer's disease (AD) genes (that was correlated with loneliness in this sample, although gene expression analyses controlled for AD diagnosis). These results identify novel targets for future mechanistic studies of gene networks in nucleus accumbens and gene regulatory mechanisms across a variety of diseases exacerbated by loneliness.

Whale's tail technique: A case series

The Whale's tail technique performed to obtain maximum interdental papilla fill in the anterior region after placement of bone grafts. This study aims to assess the clinical efficacy of this new technique. This report describes a series of three cases with a probing depth of 6–7 mm in the maxillary anterior teeth and their treatment with Whale's tail technique to obtain regeneration and maximum papilla preservation. The cases in this report showed a pocket depth reduction of 3-4mm and a clinical attachment gain of 3-4mm. The application of the “Whale's tail” flap leads to clinically significant improvement of hard and soft tissue conditions and allows regeneration of wide intrabony defects involving the maxillary anterior teeth with notable interdental diastemas, maintaining interproximal tissue to recreate a functional attachment with esthetic results.

Balancing Biomechanical Constraints: Optimal Escape Speeds When There Is a Trade-off between Speed and Maneuverability

The ability for prey to escape a pursuing predator is dependent both on the prey's speed away from the threat and on their ability to rapidly change directions, or maneuverability. Given that the biomechanical trade-off between speed and maneuverability limits the simultaneous maximization of both performance traits, animals should not select their fastest possible speeds when running away from a pursuing predator but rather a speed that maximizes the probability of successful escape. We explored how variation in the relationship between speed and maneuverability-or the shape of the trade-off-affects the optimal choice of speed for escaping predators. We used tablet-based games that simulated interactions between predators and prey (human subjects acting as predators attempting to capture "prey" moving across a screen). By defining a specific relationship between speed and maneuverability, we could test the survival of each of the possible behavioral choices available to this phenotype, i.e., the best combination of speed and maneuverability for prey fitness, based on their ability to escape. We found that the shape of the trade-off function affected the prey's optimal speed for success in escaping, the prey's maximum performance in escaping, and the breadth of speeds over which the prey's performance was high. The optimal speed for escape varied only when the trade-off between speed and maneuverability was non-linear. Phenotypes possessing trade-off functions for which maneuverability was only compromised at high speeds exhibited lower optimal speeds. Phenotypes that exhibited greater increases in maneuverability for any decrease in speed were more likely to have broader ranges of performance, meaning that individuals could attain their maximum performance across a broader range of speeds. We also found that there was a differential response of the subject's learning to these different components of locomotion. With increased experience through repeated trials, subjects were able to successfully catch faster and faster dots. However, no improvement was observed in the subject's ability to capture more maneuverable prey. Our work highlights the costs of high-speed movement on other traits, including maneuverability, which make the use of an animal's fastest speeds unlikely, even when attempting to escape predators. By investigating the shape of the trade-off functions between speed and maneuverability and the way the environment and morphology mediates this trade-off, we can begin to understand why animals choose to move at the speeds they do when they are running away from predators or attempting to capture prey.

Twins and Chronogenetics: Correlated Pathways of Development

The study of developmental processes in twins furnishes a powerful resource for examining the role of gene-action systems in guiding the course of growth [2,9].

While there is a steady and rapid progression from birth onward, the growth rate is not entirely uniform for a given child, but rather moves in episodes of acceleration and lag. The timing of the growth spurts follows a distinctive pattern for each child, and consequently a child who may be smaller than average at one age may then enter a phase of rapid growth, and ultimately catch up with or surpass his peers at a later age.

The effect of such individualized patterns of growth is that many children may change in relative size from one age to the next; and in this sense it may appear that the underlying developmental processes are erratic, rather than coherent. But if there is an underlying ground plan, a chronogenetic pattern, then the distinctive developmental gradients should unfold in synchrony for twins sharing the same genetic make-up. Episodes of acceleration and lag in growth would then occur in parallel for both twins and would presumably represent the activity of timed gene-action systems, which switch on and off according to a predetermined plan.

Genotype patterns at PICALM, CR1, BIN1, CLU, and APOE genes are associated with episodic memory

OBJECTIVE

Several genome-wide association studies (GWAS) have associated variants in late-onset Alzheimer disease (LOAD) susceptibility genes; however, these single nucleotide polymorphisms (SNPs) have very modest effects, suggesting that single SNP approaches may be inadequate to identify genetic risks. An alternative approach is the use of multilocus genotype patterns (MLGPs) that combine SNPs at different susceptibility genes.

METHODS

Using data from 1,365 subjects in the National Institute on Aging Late-Onset Alzheimer's Disease Family Study, we conducted a family-based association study in which we tabulated MLGPs for SNPs at CR1, BIN1, CLU, PICALM, and APOE. We used generalized estimating equations to model episodic memory as the dependent endophenotype of LOAD and the MLGPs as predictors while adjusting for sex, age, and education.

RESULTS

Several genotype patterns influenced episodic memory performance. A pattern that included PICALM and CLU was the strongest genotypic profile for lower memory performance (β = -0.32, SE = 0.19, p = 0.021). The effect was stronger after addition of APOE (p = 0.016). Two additional patterns involving PICALM, CR1, and APOE and another pattern involving PICALM, BIN1, and APOE were also associated with significantly poorer memory performance (β = -0.44, SE = 0.09, p = 0.009 and β = -0.29, SE = 0.07, p = 0.012) even after exclusion of patients with LOAD. We also identified genotype pattern involving variants in PICALM, CLU, and APOE as a predictor of better memory performance (β = 0.26, SE = 0.10, p = 0.010).

CONCLUSIONS

MLGPs provide an alternative analytical approach to predict an individual's genetic risk for episodic memory performance, a surrogate indicator of LOAD. Identifying genotypic patterns contributing to the decline of an individual's cognitive performance may be a critical step along the road to preclinical detection of Alzheimer disease.

Total daily physical activity and the risk of AD and cognitive decline in older adults

OBJECTIVE

Studies examining the link between objective measures of total daily physical activity and incident Alzheimer disease (AD) are lacking. We tested the hypothesis that an objective measure of total daily physical activity predicts incident AD and cognitive decline.

METHODS

Total daily exercise and nonexercise physical activity was measured continuously for up to 10 days with actigraphy (Actical®; Philips Healthcare, Bend, OR) from 716 older individuals without dementia participating in the Rush Memory and Aging Project, a prospective, observational cohort study. All participants underwent structured annual clinical examination including a battery of 19 cognitive tests.

RESULTS

During an average follow-up of about 4 years, 71 subjects developed clinical AD. In a Cox proportional hazards model adjusting for age, sex, and education, total daily physical activity was associated with incident AD (hazard ratio = 0.477; 95% confidence interval 0.273-0.832). The association remained after adjusting for self-report physical, social, and cognitive activities, as well as current level of motor function, depressive symptoms, chronic health conditions, and APOE allele status. In a linear mixed-effect model, the level of total daily physical activity was associated with the rate of global cognitive decline (estimate 0.033, SE 0.012, p = 0.007).

CONCLUSIONS

A higher level of total daily physical activity is associated with a reduced risk of AD.

Terminal dedifferentiation of cognitive abilities

OBJECTIVE

To test the cognitive dedifferentiation hypothesis that cognitive abilities become increasingly correlated in late life.

METHODS

Participants are 174 older persons without dementia at the beginning of a longitudinal clinical-pathologic cohort study. At annual intervals for 6 to 15 years prior to death, they completed a battery of cognitive performance tests from which previously established composite measures of episodic memory, semantic memory, working memory, and perceptual speed were derived. At death, there was a uniform neuropathologic assessment and levels of diffuse plaques, neuritic plaques, and neurofibrillary tangles were summarized in a composite measure. Change in the 4 cognitive outcomes was analyzed simultaneously in a mixed-effects model that allowed rate of decline to accelerate at a variable point before death.

RESULTS

On average, cognitive decline before the terminal period was relatively gradual, and rates of change in different cognitive domains were moderately correlated, ranging from 0.25 (episodic memory-working memory) to 0.46 (episodic memory-semantic memory). By contrast, cognition declined rapidly during the terminal period, and rates of change in different cognitive functions were strongly correlated, ranging from 0.83 (working memory-perceptual speed) to 0.89 (episodic memory-semantic memory, semantic memory-working memory). Higher level of plaques and tangles on postmortem examination was associated with faster preterminal decline and earlier onset of terminal decline but not with rate of terminal decline or correlations between rates of change in different cognitive functions.

CONCLUSION

In the last years of life, covariation among cognitive abilities sharply increases consistent with the cognitive dedifferentiation hypothesis.

A randomized clinical trial of anticaries therapies targeted according to risk assessment (caries management by risk assessment)

This randomized parallel group clinical trial assessed whether combined antibacterial and fluoride therapy benefits the balance between caries pathological and protective factors. Eligible, enrolled adults (n = 231), with 1-7 baseline cavitated teeth, attending a dental school clinic were randomly assigned to a control or intervention group. Salivary mutans streptococci (MS), lactobacilli (LB), fluoride (F) level, and resulting caries risk status (low or high) assays were determined at baseline and every 6 months. After baseline, all cavitated teeth were restored. An examiner masked to group conducted caries exams at baseline and 2 years after completing restorations. The intervention group used fluoride dentifrice (1,100 ppm F as NaF), 0.12% chlorhexidine gluconate rinse based upon bacterial challenge (MS and LB), and 0.05% NaF rinse based upon salivary F. For the primary outcome, mean caries increment, no statistically significant difference was observed (24% difference between control and intervention groups, p = 0.101). However, the supplemental adjusted zero-inflated Poisson caries increment (change in DMFS) model showed the intervention group had a statistically significantly 24% lower mean than the control group (p = 0.020). Overall, caries risk reduced significantly in intervention versus control over 2 years (baseline adjusted generalized linear mixed models odds ratio, aOR = 3.45; 95% CI: 1.67, 7.13). Change in MS bacterial challenge differed significantly between groups (aOR = 6.70; 95% CI: 2.96, 15.13) but not for LB or F. Targeted antibacterial and fluoride therapy based on salivary microbial and fluoride levels favorably altered the balance between pathological and protective caries risk factors.

Cognitive decline after hospitalization in a community population of older persons

OBJECTIVE

To test the hypothesis that hospitalization in old age is associated with subsequent cognitive decline.

METHODS

As part of a longitudinal population-based cohort study, 1,870 older residents of an urban community were interviewed at 3-year intervals for up to 12 years. The interview included a set of brief cognitive tests from which measures of global cognition, episodic memory, and executive function were derived. Information about hospitalization during the observation period was obtained from Medicare records.

RESULTS

During a mean of 9.3 years, 1,335 of 1,870 persons (71.4%) were hospitalized at least once. In a mixed-effects model adjusted for age, sex, race, and education, the global cognitive score declined a mean of 0.031 unit per year before the first hospitalization compared with 0.075 unit per year thereafter, a more than 2.4-fold increase. The posthospital acceleration in cognitive decline was also evident on measures of episodic memory (3.3-fold increase) and executive function (1.7-fold increase). The rate of cognitive decline after hospitalization was not related to the level of cognitive function at study entry (r = 0.01, p = 0.88) but was moderately correlated with rate of cognitive decline before hospitalization (r = 0.55, p = 0.021). More severe illness, longer hospital stay, and older age were each associated with faster cognitive decline after hospitalization but did not eliminate the effect of hospitalization.

CONCLUSION

In old age, cognitive functioning tends to decline substantially after hospitalization even after controlling for illness severity and prehospital cognitive decline.

Plasma biomarkers of depressive symptoms in older adults

The pathophysiology of negative affect states in older adults is complex, and a host of central nervous system and peripheral systemic mechanisms may play primary or contributing roles. We conducted an unbiased analysis of 146 plasma analytes in a multiplex biochemical biomarker study in relation to number of depressive symptoms endorsed by 566 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) at their baseline and 1-year assessments. Analytes that were most highly associated with depressive symptoms included hepatocyte growth factor, insulin polypeptides, pregnancy-associated plasma protein-A and vascular endothelial growth factor. Separate regression models assessed contributions of past history of psychiatric illness, antidepressant or other psychotropic medicine, apolipoprotein E genotype, body mass index, serum glucose and cerebrospinal fluid (CSF) τ and amyloid levels, and none of these values significantly attenuated the main effects of the candidate analyte levels for depressive symptoms score. Ensemble machine learning with Random Forests found good accuracy (~80%) in classifying groups with and without depressive symptoms. These data begin to identify biochemical biomarkers of depressive symptoms in older adults that may be useful in investigations of pathophysiological mechanisms of depression in aging and neurodegenerative dementias and as targets of novel treatment approaches.

Vitamin B12, cognition, and brain MRI measures: a cross-sectional examination

OBJECTIVE

To investigate the interrelations of serum vitamin B12 markers with brain volumes, cerebral infarcts, and performance in different cognitive domains in a biracial population sample cross-sectionally.

METHODS

In 121 community-dwelling participants of the Chicago Health and Aging Project, serum markers of vitamin B12 status were related to summary measures of neuropsychological tests of 5 cognitive domains and brain MRI measures obtained on average 4.6 years later among 121 older adults.

RESULTS

Concentrations of all vitamin B12-related markers, but not serum vitamin B12 itself, were associated with global cognitive function and with total brain volume. Methylmalonate levels were associated with poorer episodic memory and perceptual speed, and cystathionine and 2-methylcitrate with poorer episodic and semantic memory. Homocysteine concentrations were associated with decreased total brain volume. The homocysteine-global cognition effect was modified and no longer statistically significant with adjustment for white matter volume or cerebral infarcts. The methylmalonate-global cognition effect was modified and no longer significant with adjustment for total brain volume.

CONCLUSIONS

Methylmalonate, a specific marker of B12 deficiency, may affect cognition by reducing total brain volume whereas the effect of homocysteine (nonspecific to vitamin B12 deficiency) on cognitive performance may be mediated through increased white matter hyperintensity and cerebral infarcts. Vitamin B12 status may affect the brain through multiple mechanisms.

The relationship between lay and technical views of Escherichia coli O157 risk

Here, we bring together and contrast lay (accessible primarily through social science methodologies) and technical (via risk assessment and epidemiological techniques) views of the risk associated with the Escherichia coli O157 pathogen using two case study areas in the Grampian region of Scotland, and North Wales. Epidemiological risk factors of contact with farm animals, visiting farms or farm fields and having a private water supply were associated with postcode districts of higher than average disease incidence in the human population. However, this was not the case for the epidemiological risk factor of consumption of beef burgers, which was independent of disease incidence in the postcode district of residence. The proportion of the population expressing a high knowledge of E. coli O157 was greatest in high-incidence disease districts compared with low-incidence areas (17% cf. 7%). This supports the hypothesis that in high-disease-incidence areas, residents are regularly exposed to information about the disease through local cases, the media, local social networks, etc. or perhaps that individuals are more likely to be motivated to find out about it. However, no statistically significant difference was found between high- and low-incidence postcode districts in terms of the proportion of the population expressing a high likelihood of personal risk of infection (10% cf. 14%), giving a counterintuitive difference between the technical (epidemiological and quantitative microbiological risk assessment (QMRA)) and the lay assessment of E. coli O157 risk. This suggests that lay evaluations of E. coli O157 risk reflect intuitive and experience-based estimates of the risk rather than probabilistic estimates. A generally strong correspondence was found in terms of the rank order given to potential infection pathways, with environment and foodborne infection routes dominating when comparing public understanding with technical modelling results. Two general conclusions follow from the work. First, that integrative research incorporating both lay and technical views of risk is required in order that informed decisions can be made to handle or treat the risk by the groups concerned (e.g. the public, policy makers/risk managers, etc.). Second, when communicating risk, for example, through education programmes, it is important that this process is two-way with risk managers (e.g. including Food Standards Agency officials and communications team, public health infection control and environmental health officers) both sharing information with the public and stakeholder groups, as well as incorporating public knowledge, values and context (e.g. geographical location) into risk-management decisions.

Hemoglobin level in older persons and incident Alzheimer disease: prospective cohort analysis

OBJECTIVE

To test the hypothesis that level of hemoglobin is associated with incident Alzheimer disease (AD).

METHODS

A total of 881 community-dwelling older persons participating in the Rush Memory and Aging Project without dementia and a measure of hemoglobin level underwent annual cognitive assessments and clinical evaluations for AD.

RESULTS

During an average of 3.3 years of follow-up, 113 persons developed AD. In a Cox proportional hazards model adjusted for age, sex, and education, there was a nonlinear relationship between baseline level of hemoglobin such that higher and lower levels of hemoglobin were associated with AD risk (hazard ratio [HR] for the quadratic of hemoglobin 1.06, 95% confidence interval [CI] 1.01-1.11). Findings were unchanged after controlling for multiple covariates. When compared to participants with clinically normal hemoglobin (n = 717), participants with anemia (n = 154) had a 60% increased hazard for developing AD (95% CI 1.02-2.52), as did participants with clinically high hemoglobin (n = 10, HR 3.39, 95% CI 1.25-9.20). Linear mixed-effects models showed that lower and higher hemoglobin levels were associated with a greater rate of global cognitive decline (parameter estimate for quadratic of hemoglobin = -0.008, SE -0.002, p < 0.001). Compared to participants with clinically normal hemoglobin, participants with anemia had a -0.061 z score unit annual decline in global cognitive function (SE 0.012, p < 0.001), as did participants with clinically high hemoglobin (-0.090 unit/year, SE 0.038, p = 0.018).

CONCLUSIONS

In older persons without dementia, both lower and higher hemoglobin levels are associated with an increased hazard for developing AD and more rapid cognitive decline.

Quantitative genetic variation for thermal performance curves within and among natural populations of Drosophila serrata

Thermal performance curves (TPCs) provide a powerful framework for studying the evolution of continuous reaction norms and for testing hypotheses of thermal adaptation. Although featured heavily in comparative studies, the framework has been comparatively underutilized for quantitative genetic tests of thermal adaptation. We assayed the distribution of genetic (co)variance for TPC (locomotor activity) within and among three natural populations of Drosophila serrata and performed replicated tests of two hypotheses of thermal adaptation--that 'hotter is better' and that a generalist-specialist trade-off underpins the evolution of thermal sensitivity. We detected significant genetic variance within, and divergence among, populations. The 'hotter is better' hypothesis was not supported as the genetic correlations between optimal temperature (T(opt)) and maximum performance (z(max)) were consistently negative. A pattern of variation consistent with a generalist-specialist trade-off was detected within populations and divergence among populations indicated that performance curves were narrower and had higher optimal temperatures in the warmer, but less variable tropical population.

Change in risk of Alzheimer disease over time

OBJECTIVE

To assess whether the risk of incidence of Alzheimer disease (AD) varies over time. The increase in numbers of people at the oldest ages in the population will bring an increase in the number of people with AD. Projections of the size of the increase assume the risk of AD is constant.

METHODS

All persons age 65 or older in a biracial, geographically defined area were invited to participate in a home interview every 3 years. From the approximately 10,000 participants, stratified random samples were selected for detailed clinical evaluation. At each cycle, individuals determined free of AD in a previous cycle, either by examination or by high score on cognitive function tests, were sampled in the subsequent cycle for evaluation for incident AD. The evaluations for disease were structured and uniform across time. These analyses include 1,695 subjects evaluated for incident disease from 1997 through 2008.

RESULTS

AD developed in 360 participants. Change over time in risk of incident disease was assessed in logistic regression analyses including evaluation date and controlling for age, gender, education, race, interval from disease-free designation to evaluation for incident disease, and sample design. The time variable (in years) was not significant (odds ratio = 0.970, 95% confidence interval = 0.902 to 1.044).

CONCLUSIONS

The null relation of evaluation date to disease incidence suggests no recent change in risk of AD over time, and supports this assumption for projections of AD.

Neurodegenerative basis of age-related cognitive decline

OBJECTIVE

To assess the contribution of dementia-related neuropathologic lesions to age-related and disease-related change in cognitive function.

METHODS

A total of 354 Catholic nuns, priests, and brothers had annual clinical evaluations for up to 13 years, died, and underwent brain autopsy. The clinical evaluations included detailed testing of cognitive function from which previously established composite measures of global cognition and specific cognitive functions were derived. As part of a uniform neuropathologic evaluation, the density of neurofibrillary tangles was summarized in a composite measure and the presence of Lewy bodies and gross and microscopic cerebral infarction was noted.

RESULTS

During follow-up, rate of global cognitive decline was gradual at first and then more than quadrupled in the last 4 to 5 years of life consistent with the onset of progressive dementia. Neurofibrillary tangles, cerebral infarction, and neocortical Lewy bodies all contributed to gradual age-related cognitive decline and little age-related decline was evident in the absence of these lesions. Neurofibrillary tangles and neocortical Lewy bodies contributed to precipitous disease-related cognitive decline, but substantial disease-related decline was evident even in the absence of these lesions.

CONCLUSION

Mild age-related decline in cognitive function is mainly due to the neuropathologic lesions traditionally associated with dementia.

Cognitive activity and the cognitive morbidity of Alzheimer disease

OBJECTIVE

To test the hypothesis that frequent cognitive activity predicts slower cognitive decline before dementia onset in Alzheimer disease (AD) and faster decline thereafter.

METHODS

As part of a longitudinal cohort study, older residents of a geographically defined population were assessed at 3-year intervals with brief cognitive performance tests from which a composite measure of global cognition was derived. After each wave of testing, a subset was sampled for clinical evaluation. The present analyses are based on 1,157 participants. They were free of dementia at study enrollment at which time they rated frequency of participation in common cognitively stimulating activities from which a previously validated summary measure was derived. They were sampled for clinical evaluation a mean of 5.6 years after enrollment and subsequently followed a mean of 5.7 years with brief cognitive performance testing at 3-year intervals.

RESULTS

On clinical evaluation, 614 people had no cognitive impairment, 395 had mild cognitive impairment, and 148 had AD. During follow-up, the annual rate of global cognitive decline in persons without cognitive impairment was reduced by 52% (estimate = 0.029, SE = 0.010, p = 0.003) for each additional point on the cognitive activity scale. In the mild cognitive impairment group, cognitive decline rate was unrelated to cognitive activity (estimate = -0.019, SE = 0.018, p = 0.300). In AD, the mean rate of decline per year increased by 42% (estimate = 0.075, SE = 0.021, p < 0.001) for each point on the cognitive activity scale.

CONCLUSION

Mentally stimulating activity in old age appears to compress the cognitive morbidity associated with AD by slowing cognitive decline before dementia onset and hastening it thereafter.

Temporal course of depressive symptoms during the development of Alzheimer disease

OBJECTIVE

To characterize change in depressive symptoms before and after the onset of dementia in Alzheimer disease (AD).

METHOD

We used data from the Chicago Health and Aging Project, a longitudinal cohort study of risk factors for AD in a geographically defined population of old people. Two subsets were analyzed. In 357 individuals who developed incident AD during the study, self-report of depressive symptoms (Center for Epidemiologic Studies Depression Scale) was obtained at 3-year intervals for a mean of 8 to 9 years. In 340 individuals who agreed to annual data collection, informant report of depressive symptoms (Hamilton Depression Rating Scale) was obtained for a mean of 3 years after a diagnosis of AD (n = 107), mild cognitive impairment (n = 81), or no cognitive impairment (n = 152).

RESULTS

The incident AD group reported a barely perceptible increase in depressive symptoms during 6 to 7 years of observation before the diagnosis (0.04 symptoms per year) and no change during 2 to 3 years of observation after the diagnosis except for a slight decrease in positive affect. In those with annual follow-up, neither AD nor its precursor, mild cognitive impairment, was associated with change in informant report of depressive symptoms during a mean of 3 years of observation.

CONCLUSION

Depressive symptoms show little change during the development and progression of AD to a moderate level of dementia severity.