Cerebrospinal fluid biomarkers for Alzheimer's disease: the role of apolipoprotein E genotype, age, and sex

Framingham Risk Score and the Risk of Progression from Mild Cognitive Impairment to Dementia

BACKGROUND

Mild cognitive impairment (MCI) often represents the clinical manifestation of cognitive deterioration preceding Alzheimer's disease (AD). Currently, there are no reliable approaches for an objective evaluation of the risk of developing AD in MCI patients.

OBJECTIVE

The aim of this study was to verify whether the Framingham cardiovascular risk profile (FCRP) could be useful to identify patients at the highest risk of conversion from MCI to AD.

METHODS

Patients with amnestic MCI (aMCI) were carefully investigated to assess their vascular risk profile. They were also submitted to a comprehensive neuropsychological evaluation. The FCRP was calculated for each patient and the apolipoprotein E (ApoE) genotype was determined from peripheral blood cells. The main outcome was defined as a conversion to AD within 24 months after inclusion.

RESULTS

385 consecutive aMCI subjects were included. Age, FCRP, and vascular age showed a fairly predictive value on conversion to AD. Selecting the subpopulation of ApoE ɛ4 carriers, we observed that FCRP had an increased performance in predicting the conversion. The rate of conversion increased from 12.5% in the FCRP low-risk group to 43.2% in the high-risk group (p < 0.0001). ApoE ɛ4 carriers had a 3.7-times increased probability of conversion with respect to the other subjects (p < 0.0001).

CONCLUSIONS

FCRP assessment could be considered a reliable approach to predict conversion to AD in aMCI subjects. The presence of ApoE ɛ4 increases significantly the risk of conversion. These data confirm the narrow relationship between genetic and vascular risk factors in influencing the evolution of cognitive impairment.

Factors that influence the levels of cerebrospinal fluid biomarkers in memory clinic patients

BACKGROUND

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ), phospho tau (P-tau) and total tau (T-tau) are used increasingly to support a clinical diagnosis of Alzheimer's disease. The diagnostic power of these biomarkers has been reported to vary among different studies' results. The results are poorer when heterogeneous groups of patients have been included compared to studies where patients with Alzheimer's dementia (AD) and healthy controls have been studied. The aim of this study was to examine if age, APOE genotype and sex were associated with the levels of CSF biomarkers among patients referred to a memory clinic.

METHODS

We included 257 patients from two memory clinics who had been assessed for dementia, including lumbar puncture.

RESULTS

The mean age of the patients was 68.1 (SD: 8.0) years; 50.2% were women and 66.5% were APOE ε4 positive. Of these patients, 80.5% were diagnosed with AD or amnestic MCI. Both APOE ε4 and increasing age were associated with decreasing levels of Aβ, but not the levels of the tau proteins. In multiple regression analyses, disease stage, defined as a MMSE ≥25 or <25, influenced factors associated with the CSF biomarkers. Among those with MMSE score ≥ 25, age, APOE ε4 genotype, and MMSE score, in addition to a diagnosis of AD, were associated with Aβ level, with an explained variance of 0.43. When using P-tau or T-tau as a dependent variable, the presence of one or two APOE ε4 alleles, and MMSE score influenced the results, in addition to the diagnosis of AD. The explained variance was lower for P-tau (0.26) and for T-tau (0.32). Among those with MMSE <25, these variables explained very little of the variance. There were no gender differences.

CONCLUSIONS

We found that factors in addition to a diagnosis of AD, were associated with the levels of CSF biomarkers. Among those with MMSE ≥25, lower levels of Aβ were associated with several factors including increasing age. This is not reflected in clinical practice, where age-specific cutoffs exist only for T-tau. In this study, age was not associated with the levels of tau proteins.

Fear and Uncertainty Do Not Influence Reported Willingness to Undergo Lumbar Punctures in a U.S. Multi-Cultural Cohort

Cerebrospinal fluid (CSF) biomarkers for Alzheimer’s disease and related disorders can provide early and accurate prediction of underlying neuropathology even when the clinical symptoms are mild, but lumbar punctures (LP) to obtain CSF can be perceived as frightening and invasive. We previously demonstrated that this negative perception of the LP is strongly associated with a negative LP experience in terms of discomfort and complications, but it is not known what factors can lead to a negative perception of the LP. It has also been proposed that LP is less well-perceived by adults in the U.S. compared to Europe and elsewhere, although there is a paucity of primary data to support this. To address these knowledge gaps, we conducted a survey of 237 younger and older adults in the Atlanta area including a significant number born outside of the U.S. (n = 82, 34%) to determine demographic, medical, and experiential factors associated with the perception of LP as well as the willingness to undergo LP for medical or research purposes. Our results show that one in four respondents in this cohort with limited first-hand LP experience viewed the LP as a frightening invasive procedure, but the majority (89%) were willing to undergo LP for medical reasons. General awareness of the LP was associated with both standard and negative views of the LP, but perception did not influence willingness to undergo the procedure. Multi-variate models showed that higher annual household income, not place of birth or past experience, was associated with greater willingness to undergo LPs. We conclude that Americans (born in the U.S. or abroad) are not resistant to LPs if there is useful information to improve their health, although there is limited enthusiasm to undergo LPs solely for research purposes. At the same time, we failed to find modifiable factors to improve the perception of LP among those who already perceive it as frightening and invasive. Future recruitment effort should target adults with no preconceived notion of the LP with emphasis on data related to safety and tolerability.

Is ApoE ɛ 4 a good biomarker for amyloid pathology in late onset Alzheimer's disease?

Amyloid plaques are pathological hallmarks of Alzheimer’s Disease (AD) and biomarkers such as cerebrospinal fluid (CSF) β-amyloid 1–42 (Aβ1-42) and amyloid positron emission tomographic (PET) imaging are important in diagnosing amyloid pathology in vivo. ɛ4 allele of the Apolipoprotein E gene (ApoE ɛ 4), which is a major genetic risk factor for late onset AD, is an important genetic biomarker for AD pathophysiology. It has been shown that ApoE ɛ 4 is involved in Aβ deposition and formation of amyloid plaques. Studies have suggested the utility of peripheral blood ApoE ɛ 4 in AD diagnosis and risk assessment. However it is still a matter of debate whether ApoE ɛ 4 status would improve prediction of amyloid pathology and represent a cost-effective alternative to amyloid PET or CSF Aβ in resource-limited settings in late onset AD. Recent research suggest that the mean prevalence of PET amyloid-positivity is 95% in ApoE ɛ 4-positive AD patients. This short review aims to provide an updated information on the relationship between ApoE ɛ 4 and amyloid biomarkers.