Learning and recall in subjects at genetic risk for Alzheimer's disease

Modern Scores for Traditional Tests - Review of the Diagnostic Potential of Scores Derived from Word List Learning Tests in Mild Cognitive Impairment and Early Alzheimer's Disease

Episodic memory impairments are one of the early hallmarks in Alzheimer's Disease. In the clinical diagnosis and research, episodic memory impairment is typically assessed using word lists that are repeatedly presented to and recalled by the participant across several trials. Until recently, total learning scores, which consist of the total number of words that are recalled by participants, were almost exclusively used for diagnostic purposes. The present review aims at summarizing evidence on additional scores derived from the learning trials which have recently been investigated more frequently regarding their diagnostic potential. These scores reflect item acquisition, error frequencies, strategy use, intertrial fluctuations, and recall consistency. Evidence was summarized regarding the effects of clinical status on these scores. Preclinical, mild cognitive impairment and mild Alzheimer's Disease stages were associated with a pattern of reduced item acquisition, more errors, less strategy use, and reduced access of items, indicating slowed and erroneous encoding. Practical implications and limitations of the present research will be discussed.

APOE ε4 allele is associated with worse performance in memory dimensions of the mini-mental state examination: the Bambuí Cohort Study of Aging

OBJECTIVE

This study aimed to investigate the correlation between apolipoprotein E (APOE) ε4 and the mini-mental state examination (MMSE) dimension in an elderly population, using baseline data from the Bambui (Brazil) Cohort Study of Aging.

DESIGN

We conducted a community-based cross-sectional study.

SETTING

The study took place at Bambui city, Minas Gerais State, Southeast Brazil.

PARTICIPANTS

A total of 1408 (87.7%) cohort participants had complete information on the MMSE and health measures.

MEASUREMENTS

The association between each of five dimensions (concentration, language/praxis, orientation, attention, and memory) underlying the MMSE and APOE ε4 allele was assessed using multivariate linear regression models. Potential confounding variables included sociodemographic factors and selected biomarkers.

RESULTS

The main finding is a strong negative association between the presence of APOE ε4 allele and memory dimension in the MMSE (fully adjusted β coefficient = -0.14; 95% confidence interval: -0.27 to -0.04; p = 0.016). No other cognitive dimensions showed significant associations with the APOE ε4 allele.

CONCLUSION

This study is the first to investigate the association between dimensions of the MMSE, obtained from principal component analysis and APOE ε4 carrier status in community-dwelling older adults taking into account a range of potential confounding factors. We found a strong negative association between the presence of APOE ε4 allele and scores on memory dimension of the MMSE, but no effect on other dimensions. Our results reinforce previous data on the literature that APOE ε4 allele has a significant effect on cognitive performance that can be detected even in screening tests, such as the MMSE.

Cognitive changes preceding clinical symptom onset of mild cognitive impairment and relationship to ApoE genotype

BACKGROUND

This study had two goals (1) to evaluate changes in neuropsychological performance among cognitively normal individuals that might precede the onset of clinical symptoms, and (2) to examine the impact of Apolipoprotein E (ApoE) genotype on these changes.

METHODS

Longitudinal neuropsychological, clinical assessments and consensus diagnoses were completed prospectively in 268 cognitively normal individuals. The mean duration of follow-up was 9.2 years (+/- 3.3). 208 participants remained normal and 60 developed cognitive decline, consistent with a diagnosis of MCI or dementia. Cox regression analyses were completed, for both baseline scores and rate of change in scores, in relation to time to onset of clinical symptoms. Analyses were completed both with and without ApoE-4 status included. Interactions with ApoE-4 status were also examined.

RESULTS

Lower baseline test scores, as well as greater rate of change in test scores, were associated with time to onset of clinical symptoms (p<0.001). The mean time from baseline to onset of clinical symptoms was 6.15 (+/- 3.4) years. The presence of an ApoE-4 allele doubled the risk of progression. The rate of change in two of the test scores was significantly different in ApoE-4 carriers vs. non-carriers.

CONCLUSIONS

Cognitive performance declines prior to the onset of clinical symptoms that are a harbinger of a diagnosis of MCI. Cognitive changes in normal individuals who will subsequently decline may be observed at least 6.5 years prior to symptom onset. In addition, the risk of decline is doubled among individuals with an ApoE-4 allele.

HIV-associated neurocognitive disease: case studies and suggestions for diagnosis and management in different patient subgroups

The incidence of HIV-associated dementia has decreased significantly with the introduction of combination antiretroviral therapy; however, milder or more subtle forms of neurocognitive disorders associated with HIV appear to remain common. There is a lack of consensus on when to screen and on which methods are most appropriate for identifying patients at risk of neurocognitive impairment. Multiple factors (demographic, social, genetic, psychological and medical) can play a role in its aetiology and progression, including potential central nervous system toxicity of antiviral therapy. It is important to identify these factors in order to apply relevant management strategies. In this review, we discuss a series of case studies that address some of the challenges presented by the diagnosis and management of HIV-associated neurocognitive impairment in different patient types.

Impact of apolipoprotein E ε4 and HIV on cognition and brain atrophy: antagonistic pleiotropy and premature brain aging

OBJECTIVE

The apolipoprotein E (APOE) ε4 allele may accelerate the progression of HIV disease, and increase the risk for developing HIV-associated neurocognitive disorder (HAND). Whether APOEε4 allele(s) and age may influence brain atrophy in HIV patients is unknown and was evaluated.

METHODS

Automated morphometry on magnetic resonance images, using FreeSurfer analyses, neuropsychological testing and APOE genotyping were performed in 139 subjects [70 seronegative controls (SN); 69 clinically-stable HIV subjects].

RESULTS

Compared to SN, HIV subjects had smaller volumes throughout the brain regardless of their HAND status. Compared to APOEε4- subjects, SN controls with APOEε4 had better memory and larger global brain volumes (cerebral white matter and cortex) while HIV subjects with the APOEε4 allele(s) had poorer cognition (verbal fluency, learning, executive function and memory) and smaller cerebral and cerebellar white matter and subcortical structures. Further stratification of age showed that younger (<50 years) APOEε4+SN subjects had larger putamen and cerebral white matter, while younger APOEε4+HIV subjects had poorer performance on verbal fluency and smaller brain volumes [3-way (HIV-status×APOEε4×Age) interaction-p-values=0.005 to 0.03].

INTERPRETATION

These findings suggest that APOEε4 allele(s) may show antagonistic pleiotropy on cognition and brain atrophy in SN controls, but may lead to premature aging with neurodegeneration in younger HIV patients prior to the development of HAND. Potential mechanisms for such interactions may include stronger neuro-inflammation or greater amyloid deposition in younger HIV subjects with APOEε4 allele(s). Early screening for the APOEε4 allele and brain atrophy with morphometry may guide neuroprotective intervention of cognitively normal HIV subjects prior to the development of HAND. Longitudinal follow-up studies and larger sample sizes are needed to validate these cross-sectional results.

The effects of cholesterol on learning and memory

Cholesterol is vital to normal brain function including learning and memory but that involvement is as complex as the synthesis, metabolism and excretion of cholesterol itself. Dietary cholesterol influences learning tasks from water maze to fear conditioning even though cholesterol does not cross the blood brain barrier. Excess cholesterol has many consequences including peripheral pathology that can signal brain via cholesterol metabolites, pro-inflammatory mediators and antioxidant processes. Manipulations of cholesterol within the central nervous system through genetic, pharmacological, or metabolic means circumvent the blood brain barrier and affect learning and memory but often in animals already otherwise compromised. The human literature is no less complex. Cholesterol reduction using statins improves memory in some cases but not others. There is also controversy over statin use to alleviate memory problems in Alzheimer's disease. Correlations of cholesterol and cognitive function are mixed and association studies find some genetic polymorphisms are related to cognitive function but others are not. In sum, the field is in flux with a number of seemingly contradictory results and many complexities. Nevertheless, understanding cholesterol effects on learning and memory is too important to ignore.

Postmenopausal hormone therapy and cognitive outcomes: the Women's Health Initiative Memory Study (WHIMS)

This review discusses major findings from the Women's Health Initiative Memory Study (WHIMS). WHIMS reported hormone therapy (HT)--conjugated equine estrogen (CEE) with or without medroxyprogesterone acetate (MPA)--increased the risk for dementia (HR 1.76 [95% CI, 1.19-2.60]; P=0.005) and global cognitive decline, with a mean decrement relative to placebo of 0.21 points on the Modified Mini Mental State Examination (3MS) (P=0.006) in women age 65 and older. A subset of WHIMS participants joined the ancillary WHI Study of Cognitive Aging (WHISCA) trials, in which domain-specific cognitive tests and mood were measured annually. Compared with placebo, CEE+MPA had a negative impact on verbal memory over time (P=0.01); and CEE-Alone was associated with lower spatial rotational ability (P < or = 0.01) at the initial assessment, but the difference diminished over time. The ancillary WHIMS-MRI study measured subclinical cerebrovascular disease to possibly explain the negative cognitive findings reported by WHIMS and the increased clinical stroke in older women reported by the WHI. WHIMS-MRI reported that while CEE+MPA and CEE-Alone were not associated with increased ischemic brain lesion volume relative to placebo; both CEE+MPA and CEE-Alone were associated with lower mean brain volumes in the hippocampus (P=0.05); frontal lobe (P=0.004); and total brain (P=0.07). HT-associated reductions in hippocampal volumes were greatest in women with baseline 3MS scores < or = 90.

The apolipoprotein E epsilon4 allele and memory performance in HIV-1 seropositive subjects: differences at baseline but not after acute oral lorazepam challenge

RATIONALE

The APOE epsilon4 allele, an established genetic risk factor for late-onset Alzheimer's disease, has been linked to an increased risk for dementia especially in older individuals with HIV-1 infection. This allele has also been associated with increased memory impairment following oral lorazepam challenge in healthy elderly. Lorazepam and other benzodiazepines are widely prescribed in individuals with HIV-1 infection who are at increased risk for cognitive impairment.

OBJECTIVE

The aim of this study was to examine if the epsilon4 allele influences lorazepam-induced memory deficits in this population.

MATERIALS AND METHODS

Forty-one non-demented, HIV-1 seropositive adults (15 epsilon4 carriers, mean age = 43.47 +/- 8.25; 26 epsilon4 non-carriers, mean age = 46.77 +/- 8.56) participated in a double-blind, placebo-controlled crossover design, receiving single acute oral doses of lorazepam 0.5, 1.0 mg, or placebo over three sessions, each 1 week apart. Standardized neuropsychological assessments, including measures of immediate and delayed verbal recall, were conducted at baseline and at 1, 2.5, and 5 h post-drug administration in each condition.

RESULTS

Acute lorazepam administration produced dose- and time-dependent impairments in measures of verbal recall. However, the e4 allele did not modulate these adverse effects. An APOE epsilon4 group by time interaction was also found such that the APOE-epsilon4-positive subjects had significantly better immediate and delayed verbal recall than the negative subjects at baseline assessment, but the groups did not significantly differ at any subsequent time point.

CONCLUSION

Future studies should clarify the role of epsilon4 in the modulation of drug-induced cognitive toxicity and baseline performance and their relationship to progressive decline, especially in older individuals with HIV-1 infection, a group at increased risk for dementia.

Neuropsychological and neuroimaging changes in preclinical Alzheimer's disease

Alzheimer's disease (AD) is a common, devastating form of dementia. With the advent of promising symptomatic treatment, the importance of recognizing AD at its very earliest stages has increased. We review the extant neuropsychological and neuroimaging literature on preclinical AD, focusing on longitudinal studies of initially nondemented individuals and cross-sectional investigations comparing at-risk with normal individuals. We systematically reviewed 91 studies of neuropsychological functioning, structural neuroimaging, or functional neuroimaging in preclinical AD. The neuropsychological studies indicated that preclinical AD might be characterized by subtle deficits in a broad range of neuropsychological domains, particularly in attention, learning and memory, executive functioning, processing speed, and language. Recent findings from neuroimaging research suggest that volume loss and cerebral blood flow or metabolic changes, particularly in the temporal lobe, may be detected before the onset of dementia. There exist several markers of a preclinical period of AD, in which specific cognitive and biochemical changes precede the clinical manifestations. The preclinical indicators of AD reflect early compromise of generalized brain integrity and temporal lobe functioning in particular.

Apolipoprotein E and cognitive performance: a meta-analysis

The epsilon4 allele of the apolipoprotein E (APOE) gene is a known risk factor for Alzheimer's disease and may also affect cognitive performance in normal aging. Evidence of the presence and magnitude of epsilon4-related cognitive deficits was examined with a meta-analysis of the available literature. Thirty-eight studies were included, and cognitive performance was collapsed into 8 domains. Results indicated significant APOE-epsilon4 group differences for global cognitive functioning, episodic memory, and executive functioning, in favor of non-epsilon4 carriers. In addition, older age and APOE-epsilon4 heterozygosity was associated with smaller epsilon4-related impairments. The meta-analysis results suggest that APOE-epsilon4 genotype does affect cognitive performance in healthy aging, although the influence is relatively small and specific to certain domains of cognitive performance.