Should the ApoE genotype be a covariate for clinical trials in Alzheimer disease?

Response adaptive randomization design for a two-stage study with binary response

Response adaptive randomization has the potential to treat more participants in better treatments in a trial to benefit participants. We propose optimal response adaptive randomization designs for a two-stage study with binary response, having the smallest expected sample size or the fewest expected number of failures. Equal randomization is used in the first stage, and data from the first stage is used to determine the adaptive sample size ratio in the second stage. In the proposed optimal designs, the type I error rate and the statistical power are calculated from the asymptotic normal distributions. The new designs that minimize the expected number of failures have the advantage over the existing optimal randomized designs to substantially reduce the number of failures.

Sexual Dimorphism in the 3xTg-AD Mouse Model and Its Impact on Pre-Clinical Research

Female sex is a leading risk factor for developing Alzheimer’s disease (AD). Sexual dimorphism in AD is gaining attention as clinical data show that women are not only more likely to develop AD but also to experience worse pathology and faster cognitive decline. Pre-clinical AD research in animal models often neglects to address sexual dimorphism in evaluation of behavioral or molecular characteristics and outcomes. This can compromise its translation to a clinical setting. The triple-transgenic AD mouse model (3xTg-AD) is a commonly used but unique AD model because it exhibits both amyloid and tau pathology, essential features of the human AD phenotype. Mounting evidence has revealed important sexually dimorphic characteristics of this animal model that have yet to be reviewed and thus, are often overlooked in studies using the 3xTg-AD model. In this review we conduct a thorough analysis of reports of sexual dimorphism in the 3xTg-AD model including findings of molecular, behavioral, and longevity-related sex differences in original research articles through August 2020. Importantly, we find results to be inconsistent, and that strain source and differing methodologies are major contributors to lack of consensus regarding traits of each sex. We first touch on the nature of sexual dimorphism in clinical AD, followed by a brief summary of sexual dimorphism in other major AD murine models before discussing the 3xTg-AD model in depth. We conclude by offering four suggestions to help unify pre-clinical mouse model AD research inspired by the NIH expectations for considering sex as a biological variable.

Genome-wide association study identifies susceptibility loci of brain atrophy to NFIA and ST18 in Alzheimer's disease

To identify genetic variants influencing cortical atrophy in Alzheimer's disease (AD), we performed genome-wide association studies (GWAS) of mean cortical thicknesses in 17 AD-related brain. In this study, we used neuroimaging and genetic data of 919 participants from the Alzheimer's Disease Neuroimaging Initiative cohort, which include 268 cognitively normal controls, 488 mild cognitive impairment, 163 AD individuals. We performed GWAS with 3,041,429 single nucleotide polymorphisms (SNPs) for cortical thickness. The results of GWAS indicated that rs10109716 in ST18 (ST18 C2H2C-type zinc finger transcription factor) and rs661526 in NFIA (nuclear factor I A) genes are significantly associated with mean cortical thicknesses of the left inferior frontal gyrus and left parahippocampal gyrus, respectively. The rs661526 regulates the expression levels of NFIA in the substantia nigra and frontal cortex and rs10109716 regulates the expression levels of ST18 in the thalamus. These results suggest a crucial role of identified genes for cortical atrophy and could provide further insights into the genetic basis of AD.

Interventional programmes to improve cognition during healthy and pathological ageing: Cortical modulations and evidence for brain plasticity

A growing body of evidence suggests that healthy elderly individuals and patients with Alzheimer's disease retain an important potential for neuroplasticity. This review summarizes studies investigating the modulation of neural activity and structural brain integrity in response to interventions involving cognitive training, physical exercise and non-invasive brain stimulation in healthy elderly and cognitively impaired subjects (including patients with mild cognitive impairment (MCI) and Alzheimer's disease). Moreover, given the clinical relevance of neuroplasticity, we discuss how evidence for neuroplasticity can be inferred from the functional and structural brain changes observed after implementing these interventions. We emphasize that multimodal programmes, which combine several types of interventions, improve cognitive function to a greater extent than programmes that use a single interventional approach. We suggest specific methods for weighting the relative importance of cognitive training, physical exercise and non-invasive brain stimulation according to the functional and structural state of the brain of the targeted subject to maximize the cognitive improvements induced by multimodal programmes.

A rapid and cost-effective method for genotyping apolipoprotein E gene polymorphism

Background

Apolipoprotein E (ApoE) is a major cholesterol carrier and plays an important role in maintaining lipid homeostasis both in the periphery and brain. Human APOE gene is polymorphic at two single nucleotides (rs429358 and rs7412) resulting in three different alleles (ε2, ε3 and ε4). ApoE isoforms modulate the risk for a variety of vascular and neurodegenerative diseases; thus, APOE genotyping is crucial for predicting disease risk and designing individualized therapy based on APOE genotype.

Results

We have developed an APOE genotyping method that is based on allele-specific PCR methodology adapted to Real Time PCR monitored by TaqMan probe. Rather than using TaqMan probes specific for the two polymorphic sites, only one TaqMan probe is used as the polymorphic alleles are recognized by site-specific PCR primers. Each genotyping assay can be completed within 90 minutes and is applicable to high-throughput analysis. Using this protocol, we genotyped a total of 1158 human DNA samples and obtained a 100 % concordance with the APOE genotype determined by sequencing analysis.

Conclusion

The APOE genotyping assay we have developed is accurate and cost-effective. In addition, our assay can readily be applied to genotyping large sample numbers. Therefore, our APOE genotyping method can be used for assessing the risk for a variety of vascular and neurodegenerative diseases that have been reported to be associated with APOE polymorphism.

Apolipoprotein E, gender, and Alzheimer's disease: an overlooked, but potent and promising interaction

Alzheimer's disease (AD) is an increasingly prevalent, fatal neurodegenerative disease that has proven resistant, thus far, to all attempts to prevent it, forestall it, or slow its progression. The ε4 allele of the Apolipoprotein E gene (APOE4) is a potent genetic risk factor for sporadic and late-onset familial AD. While the link between APOE4 and AD is strong, many expected effects, like increasing the risk of conversion from MCI to AD, have not been widely replicable. One critical, and commonly overlooked, feature of the APOE4 link to AD is that several lines of evidence suggest it is far more pronounced in women than in men. Here we review previous literature on the APOE4 by gender interaction with a particular focus on imaging-related studies.

Reduced cerebrovascular reactivity in young adults carrying the APOE ε4 allele

BACKGROUND

Functional magnetic resonance imaging (MRI) studies have shown that APOE ε2- and ε4-carriers have similar patterns of blood-oxygenation-level-dependent (BOLD) activation suggesting that we need to look beyond the BOLD signal to link APOE's effect on the brain to Alzheimer's disease (AD)-risk.

METHODS

We evaluated APOE-related differences in BOLD activation in response to a memory task, cerebrovascular reactivity using a CO2-inhalation challenge (CO2-CVR), and the potential contribution of CO2-CVR to the BOLD signal.

RESULTS

APOE ε4-carriers had the highest task-related hippocampal BOLD signal relative to non-carriers. The largest differences in CO2-CVR were between ε2- and ε4-carriers, with the latter having the lowest values. Genotype differences in CO2-CVR accounted for ∼70% of hippocampal BOLD differences between groups.

CONCLUSION

Because CO2-CVR gauges vascular health, the differential effect of APOE in young adults may reflect a vascular contribution to the vulnerability of ε4-carriers to late-life pathology. Studies confirming our findings are warranted.

Sex modifies the APOE-related risk of developing Alzheimer disease

OBJECTIVE

The APOE4 allele is the strongest genetic risk factor for sporadic Alzheimer disease (AD). Case-control studies suggest the APOE4 link to AD is stronger in women. We examined the APOE4-by-sex interaction in conversion risk (from healthy aging to mild cognitive impairment (MCI)/AD or from MCI to AD) and cerebrospinal fluid (CSF) biomarker levels.

METHODS

Cox proportional hazards analysis was used to compute hazard ratios (HRs) for an APOE-by-sex interaction on conversion in controls (n = 5,496) and MCI patients (n = 2,588). The interaction was also tested in CSF biomarker levels of 980 subjects from the Alzheimer's Disease Neuroimaging Initiative.

RESULTS

Among controls, male and female carriers were more likely to convert to MCI/AD, but the effect was stronger in women (HR = 1.81 for women; HR = 1.27 for men; interaction: p = 0.011). The interaction remained significant in a predefined subanalysis restricted to APOE3/3 and APOE3/4 genotypes. Among MCI patients, both male and female APOE4 carriers were more likely to convert to AD (HR = 2.16 for women; HR = 1.64 for men); the interaction was not significant (p = 0.14). In the subanalysis restricted to APOE3/3 and APOE3/4 genotypes, the interaction was significant (p = 0.02; HR = 2.17 for women; HR = 1.51 for men). The APOE4-by-sex interaction on biomarker levels was significant for MCI patients for total tau and the tau-to-Aβ ratio (p = 0.009 and p = 0.02, respectively; more AD-like in women).

INTERPRETATION

APOE4 confers greater AD risk in women. Biomarker results suggest that increased APOE-related risk in women may be associated with tau pathology. These findings have important clinical implications and suggest novel research approaches into AD pathogenesis.

A large ApoE ε4/ε4 homozygous cohort reveals no association with Parkinson's disease

To investigate the correlation between cognitive impairment, Parkinson's disease (PD) symptoms and ApoE ε4/ε4 homozygosity an ApoE ε4/ε4 homozygous cohort was compared with an ApoE ε3/ε3 homozygous comparison group. A total of 696 outpatients with memory complaints had undergone comprehensive neuropsychiatric assessment including interview and examination by clinical psychiatrists and neurologists as well as laboratory blood testing (including ApoE genotyping). Patients also underwent the Consortium to Establish a Registry on Alzheimer's Disease (CERAD) test battery and the Clock-Drawing Test (Shulman scoring). Of the 623 selected individuals 258 were homozygous for ApoE ε3 and 133 were homozygous for ApoE ε4, while 232 were heterozygous for ApoE ε3/ε4. Thirty patients in the entire sample were diagnosed with PD (4.8 %). In the ApoE ε4/ε4 group seven persons had PD (5.3 %), while in the ApoE ε3/ε3 comparison group nine persons were diagnosed with PD (3.5 %). In the ApoE ε3/ε4 heterozygous group we found 14 (6.03 %) subjects meeting criteria for PD, P = 0.406. This is to our knowledge the largest retrospective cohort study to date of ApoE ε4 homozygous carriers. In comparison with the ApoE ε3 homozygous carriers in our study, subjects who were homozygous for ApoE ε4 demonstrated a slightly but statistically insignificant higher prevalence of PD, while in the ApoE ε3/ε4 heterozygous group we detected the highest rate of probands diagnosed with PD. We conclude that there is no correlation between allele combinations of ApoE ε3 and ApoE ε4 in their heterozygote and homozygote composition and prevalence of PD.

Serum folate and B12 levels in association with cognitive impairment among seniors: results from the VELESTINO study in Greece and meta-analysis

OBJECTIVE

To summarize existing evidence on the effect of serum folate and vitamin B12 levels on cognitive impairment among elders via a meta-analysis, also including unpublished data from a cross-sectional study of seniors ( > 65 years) residing in Velestino, Greece.

METHOD

Serum measurements and Mini-Mental State Examination (MMSE) assessments were available for 593 Velestinians. In addition, 12 studies availing data on folate blood levels (N = 9,747) and 9 on B12 (N = 8,122) were identified following a search algorithm; pooled effect estimates were derived.

RESULTS

Cognitive impairment (MMSE < 24) among Velestenians was associated with lower education level in both genders; decreased social activity, depressive symptoms and low folate levels in males; older age in females. Meta-analyses showed an adverse effect of low-folate levels on cognition (OR: 1.66, 95% CI: 1.40-1.96); B12 was nonsignificantly associated (OR: 1.11, 95% CI: 0.88-1.40).

DISCUSSION

Low folate levels are associated with cognitive impairment of seniors; underlying pathophysiological mechanisms should be further explored.

Prophylaxis and treatment of Alzheimer's disease by delivery of an adeno-associated virus encoding a monoclonal antibody targeting the amyloid Beta protein

We previously reported on a monoclonal antibody (mAb) that targeted amyloid beta (Aß) protein. Repeated injection of that mAb reduced the accumulation of Aß protein in the brain of human Aß transgenic mice (Tg2576). In the present study, cDNA encoding the heavy and light chains of this mAb were subcloned into an adeno-associated virus type 1 (AAV) vector with a 2A/furin adapter. A single intramuscular injection of 3.0×10¹⁰ viral genome of these AAV vectors into C57BL/6 mice generated serum anti-Aß Ab levels up to 0.3 mg/ml. Anti-Aß Ab levels in excess of 0.1 mg/ml were maintained for up to 64 weeks. The effect of AAV administration on Aß levels in vivo was examined. A significant decrease in Aß levels in the brain of Tg2576 mice treated at 5 months (prophylactic) or 10 months (therapeutic) of age was observed. These results support the use of AAV vector encoding anti-Aß Ab for the prevention and treatment of Alzheimer's disease.

Cognitive dysfunction and cancer: which consequences in terms of disease management?

OBJECTIVES

The aim of this review is to stress the importance of cognitive dysfunction in cancer survivors, and to discuss the way of assessing and managing these troubles in clinical practice.

METHOD

Original studies and reviews reporting the effect of cancer and chemotherapy on cognition and published since January 2000 were selected from the Medline(®) database using 'cognition' or 'cognitive function' and 'cancer' as subject headings.

RESULTS

Main reports concerned women with advanced breast cancer or children with hematological or brain cancers. Overall, chemotherapy was found to be associated with subtle and transient cognitive dysfunctions, which were detectable only with neuropsychological testing and affected most particularly memory, concentration and speed of information processing. Some factors associated with the patient, like depression, may favor cognitive impairment, while the role of others, like age or educational level, remains to be defined. Screening of patients at risk remains limited due to the lack of standardized neuropsychological tests in clinical oncology practice. Few studies have addressed the benefits of interventional strategies but methylphenidate, modafinil and erythropoietin, as well as rehabilitation in children, have shown encouraging results. Formal studies assessing the value of a multidisciplinary approach to detect and manage cognitive impairment must be recommended.

CONCLUSION

Cognitive dysfunction induced by cancer or the treatment represents a real challenge in clinical practice. Based on limited published data, few clinical recommendations can be made regarding prevention, evaluation and management of this trouble. Longitudinal studies must be conducted to evaluate its real impact on quality of life.