Leucocyte telomere length, brain volume and risk of dementia: a prospective cohort study

Telomere Length and Cognitive Function Among Middle-Aged and Older Participants From Communities Underrepresented in Aging Research: A Preliminary Study

ObjectiveAccelerated biological aging is a plausible and modifiable determinant of dementia burden facing minoritized communities but is not well-studied in these historically underrepresented populations. Our objective was to preliminarily characterize relationships between telomere length and cognitive health among American Indian/Alaska Native (AI/AN) and Black/African American (B/AA) middle-aged and older adults.MethodsThis study included data on telomere length and neuropsychological test performance from 187 participants, enrolled in one of two community-based cognitive aging cohorts and who identified their primary race as AI/AN or B/AA.ResultsNested multivariable regression models revealed preliminary evidence for associations between telomere length and cognitive performance, and these associations were partially independent of chronological age.DiscussionSmall sample size limited estimate precision; however, findings suggest future work on telomere length and cognitive health in underrepresented populations at high risk for dementia is feasible and valuable as a foundation for social and behavioral intervention research.

Telomere Length, Brain Imaging-Derived Phenotypes, and Alzheimer's Disease: Mendelian Randomization Analysis

Previous studies have reported a correlation between telomere length (TL) and Alzheimer's disease (AD); however, the specific biological mechanisms supporting this association remain unclear. We used two-sample Mendelian randomization (MR) to systematically explore the putative causal relationships between TL, brain imaging-derived phenotypes (IDPs), and AD, while further evaluating the mediating role of IDPs using both two-step MR and multivariable MR. In addition, we utilized several independent validation cohorts to repeat the analysis, further strengthening our inferences. The MR analysis showed that a longer TL was causally associated with a lower risk for AD (OR, 0.84; 95% CI, 0.75 to 0.93; P = 0.001). In addition, the subsequent two-step MR results indicate that nine brain IDPs partially mediate the effect of TL on AD. The inverse association of genetically predicted TL with AD was attenuated after adjusting for these IDPs in multivariable MR. Our study provides further evidence for the causal relationship between TL and AD, with IDPs potentially partially mediating this association. Therefore, telomere biology may be a potential pathway involved in AD development, and identifying the important role of telomeres can draw more attention to the development of telomere-related diagnostics, treatments, and AD therapies.

Telomere Length and Symptoms of Attention Deficit and Hyperactivity Disorder in Children at 6-12 Years

OBJECTIVE

To explore the association between telomere length (TL) and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6-12 years.

METHOD

Data from 1,759 children belonging to the HELIX project cohorts and the Asturias, Gipuzkoa and Valencia cohorts of INMA project were included. TL was determined by blood sample using a PCR protocol. ADHD symptoms were described by parents using the Conners' Parent Rating Scale-Revised: Short Form. Multiple negative binomial regression models adjusted for potential confounders were used to estimate associations.

RESULTS

Overall estimates showed no associations between TL and ADHD symptoms. However, we observed that a longer TL was significantly associated with a lower risk of presenting hyperactivity symptoms in children belonging to the HELIX project (IRR = 0.93, 95% CI [0.87, 0.99]; p = .022).

CONCLUSION

While our study did not find a consistent association between TL and ADHD symptoms across all cohorts, the significant association found within the HELIX cohort suggests that longer TL may be linked to a lower risk of hyperactivity symptoms. Further research is needed to explore this association in more detail.

Association of critically short telomeres with brain and blood markers of ageing and Alzheimer's disease in older adults

BACKGROUND

Accumulation of critically short telomeres (CST) is implicated in decreased tissular regenerative capacity and increased susceptibility to degenerative diseases such as Alzheimer's disease (AD). Telomere shortening has also been associated with age-related brain changes. However, it remains unclear whether CST accumulation is directly associated with AD markers or instead amplifies age-related effects, potentially increasing susceptibility of developing AD in cognitively healthy older adults.

METHODS

This cross-sectional study used baseline data of 129 community-dwelling cognitively healthy older adults from the Age-Well trial (NCT02977819), aged 65 years and older enrolled between 2016 and 2018, in France. Using linear regressions, we analyzed the relationship between an innovative marker of telomere shortening, the percentage of CST (%CST), structural, functional and molecular neuroimaging outcomes, and multiple blood-based biomarkers related to AD pathophysiology. The effect of apolipoprotein E ε4 genotype (APOE4) was assessed on these relationships using interaction analysis.

RESULTS

A higher %CST was associated with lower global kurtosis fractional anisotropy (β = -.230; P = .010), particularly in frontal and temporal regions. A higher %CST was also related to higher plasma levels of Neurofilament light chain (β = .195; P = .020) and a lower subiculum volume (β = -.206; P = .020), although these associations did not meet the threshold for multiple comparisons. %CST was not associated with AD-related neuroimaging markers, including the AD-sensitive gray matter pattern (β = -.060; P = .441), glucose metabolism pattern (β = -.099; P = .372), brain perfusion pattern (β = -.106; P = .694) or hippocampus volume (β = -.106; P = .194). In APOE4 carriers, higher %CST was associated with lower subiculum (β = -.423; P = 0.003), DG (β = -.410; P = 0.018) and CA1 volumes (β = -.373; P = 0.024), even though associations with DG and CA1 volumes did not survive multiple comparison.

CONCLUSIONS

Although an increase in %CST does not appear to be directly linked to the pathophysiology of AD in cognitively healthy older adults, it could heighten the susceptibility of APOE4 carriers to develop AD plausibly due to greater vulnerability to age-related effects. However, longitudinal studies would be necessary to determine whether %CST influences the development and progression of AD later in life.

Telomere length and cognitive function among middle-aged and older participants from communities underrepresented in aging research: A preliminary study

Objective

Accelerated biological aging is a plausible and modifiable determinant of dementia burden facing minoritized communities, but is not well-studied in these historically underrepresented populations. Our objective was to preliminarily characterize relationships between telomere length and cognitive health among American Indian/Alaska Native (AI/AN) and Black/African American (B/AA) middle-aged and older adults.

Methods

This study included data on telomere length and cognitive test performance from 187 participants, enrolled in one of two community-based cognitive aging cohorts and who identified their primary race as AI/AN or B/AA.

Results

Nested multivariable regression models revealed preliminary evidence for associations between telomere length and cognitive performance, and these associations were partially independent of chronological age.

Discussion

Small sample size limited estimate precision, however, findings suggest future work on telomere length and cognitive health in underrepresented populations at high risk for dementia is feasible and valuable as a foundation for social and behavioral intervention research.

Causal Relationship between Aging and Anorexia Nervosa: A White-Matter-Microstructure-Mediated Mendelian Randomization Analysis

This study employed a two-step Mendelian randomization analysis to explore the causal relationship between telomere length, as a marker of aging, and anorexia nervosa and to evaluate the mediating role of changes in the white matter microstructure across different brain regions. We selected genetic variants associated with 675 diffusion magnetic resonance imaging phenotypes representing changes in brain white matter. F-statistics confirmed the validity of the instruments, ensuring robust causal inference. Sensitivity analyses, including heterogeneity tests, horizontal pleiotropy tests, and leave-one-out tests, validated the results. The results show that telomere length is significantly negatively correlated with anorexia nervosa in a unidirectional manner (p = 0.017). Additionally, changes in specific white matter structures, such as the internal capsule, corona radiata, posterior thalamic radiation, left cingulate gyrus, left longitudinal fasciculus, and left forceps minor (p < 0.05), were identified as mediators. These findings enhance our understanding of the neural mechanisms, underlying the exacerbation of anorexia nervosa with aging; emphasize the role of brain functional networks in disease progression; and provide potential biological targets for future therapeutic interventions.

Correlation of telomere length in brain tissue with peripheral tissues in living human subjects

Telomeres are important to chromosomal stability, and changes in their length correlate with disease, potentially relevant to brain disorders. Assessing telomere length in human brain is invasive, but whether peripheral tissue telomere length correlates with that in brain is not known. Saliva, buccal, blood, and brain samples were collected at time points before, during, and after subjects undergoing neurosurgery (n = 35) for intractable epilepsy. DNA was isolated from samples and average telomere length assessed by qPCR. Correlations of telomere length between tissue samples were calculated across subjects. When data were stratified by sex, saliva telomere length correlated with brain telomere length in males only. Buccal telomere length correlated with brain telomere length when males and females were combined. These findings indicate that in living subjects, telomere length in peripheral tissues variably correlates with that in brain and may be dependent on sex. Peripheral tissue telomere length may provide insight into brain telomere length, relevant to assessment of brain disorder pathophysiology.

Consensus on rapid screening for prodromal Alzheimer's disease in China

Alzheimer's disease (AD) is a common cause of dementia, characterised by cerebral amyloid-β deposition, pathological tau and neurodegeneration. The prodromal stage of AD (pAD) refers to patients with mild cognitive impairment (MCI) and evidence of AD's pathology. At this stage, disease-modifying interventions should be used to prevent the progression to dementia. Given the inherent heterogeneity of MCI, more specific biomarkers are needed to elucidate the underlying AD's pathology. Although the uses of cerebrospinal fluid and positron emission tomography are widely accepted methods for detecting AD's pathology, their clinical applications are limited by their high costs and invasiveness, particularly in low-income areas in China. Therefore, to improve the early detection of Alzheimer's disease (AD) pathology through cost-effective screening methods, a panel of 45 neurologists, psychiatrists and gerontologists was invited to establish a formal consensus on the screening of pAD in China. The supportive evidence and grades of recommendations are based on a systematic literature review and focus group discussion. National meetings were held to allow participants to review, vote and provide their expert opinions to reach a consensus. A majority (two-thirds) decision was used for questions for which consensus could not be reached. Recommended screening methods are presented in this publication, including neuropsychological assessment, peripheral biomarkers and brain imaging. In addition, a general workflow for screening pAD in China is established, which will help clinicians identify individuals at high risk and determine therapeutic targets.

Cardiovascular risk burden, dementia risk and brain structural imaging markers: a study from UK Biobank

Background

Cardiovascular risk burden is associated with dementia risk and neurodegeneration-related brain structure, while the role of genetics and incident cardiovascular disease (CVD) remains unclear.

Aims

To examine the association of overall cardiovascular risk burden with the risk of major dementia subtypes and volumes of related brain regions in a large sample, and to explore the role of genetics and CVD onset.

Methods

A prospective study among 354 654 participants free of CVD and dementia (2006-2010, mean age 56.4 years) was conducted within the UK Biobank, with brain magnetic resonance imaging (MRI) measurement available for 15 104 participants since 2014. CVD risk burden was evaluated by the Framingham General Cardiovascular Risk Score (FGCRS). Dementia diagnosis was ascertained from inpatient and death register data.

Results

Over a median 12.0-year follow-up, 3998 all-cause dementia cases were identified. Higher FGCRS was associated with increased all-cause dementia risk after adjusting for demographic, major lifestyle, clinical factors and the polygenic risk score (PRS) of Alzheimer's disease. Comparing the high versus low tertile of FGCRS, the odds ratios (ORs) and 95% confidence intervals (CIs) were 1.26 (1.12 to 1.41) for all-cause dementia, 1.67 (1.33 to 2.09) for Alzheimer's disease and 1.53 (1.07 to 2.16) for vascular dementia (all ptrend<0.05). Incident stroke and coronary heart disease accounted for 14% (95% CI: 9% to 21%) of the association between FGCRS and all-cause dementia. Interactions were not detected for FGCRS and PRS on the risk of any dementia subtype. We observed an 83% (95% CI: 47% to 128%) higher all-cause dementia risk comparing the high-high versus low-low FGCRS-PRS category. For brain volumes, higher FGCRS was associated with greater log-transformed white matter hyperintensities, smaller cortical volume and smaller grey matter volume.

Conclusions

Our findings suggest that the positive association of cardiovascular risk burden with dementia risk also applies to major dementia subtypes. The association of cardiovascular risk burden with all-cause dementia is largely independent of CVD onset and genetic predisposition to dementia.

Effects of a periodic intermittent theta burst stimulation in Alzheimer's disease

BACKGROUND

Previous studies have demonstrated that excitatory repetitive transcranial magnetic stimulation (rTMS) can improve the cognitive function of patients with Alzheimer's disease (AD). Intermittent theta burst stimulation (iTBS) is a novel excitatory rTMS protocol for brain activity stimulation with the ability to induce long-term potentiation-like plasticity and represents a promising treatment for AD. However, the long-term effects of iTBS on cognitive decline and brain structure in patients with AD are unknown.

AIMS

We aimed to explore whether repeating accelerated iTBS every three months could slow down the cognitive decline in patients with AD.

METHODS

In this randomised, assessor-blinded, controlled trial, iTBS was administered to the left dorsolateral prefrontal cortex (DLPFC) of 42 patients with AD for 14 days every 13 weeks. Measurements included the Montreal Cognitive Assessment (MoCA), a comprehensive neuropsychological battery, and the grey matter volume (GMV) of the hippocampus. Patients were evaluated at baseline and after follow-up. The longitudinal pipeline of the Computational Anatomy Toolbox for SPM was used to detect significant treatment-related changes over time.

RESULTS

The iTBS group maintained MoCA scores relative to the control group (t=3.26, p=0.013) and reduced hippocampal atrophy, which was significantly correlated with global degeneration scale changes. The baseline Mini-Mental State Examination (MMSE) score, apolipoprotein E genotype and Clinical Dementia Rating were indicative of MoCA scores at follow-up. Moreover, the GMV of the left (t=0.08, p=0.996) and right (t=0.19, p=0.977) hippocampus were maintained in the active group but significantly declined in the control group (left: t=4.13, p<0.001; right: t=5.31, p<0.001). GMV change in the left (r=0.35, p=0.023) and right (r=0.36, p=0.021) hippocampus across the intervention positively correlated with MoCA changes; left hippocampal GMV change was negatively correlated with global degeneration scale (r=-0.32, p=0.041) changes.

CONCLUSIONS

DLPFC-iTBS may be a feasible and easy-to-implement non-pharmacological intervention to slow down the progressive decline of overall cognition and quality of life in patients with AD, providing a new AD treatment option.

TRIAL REGISTRATION NUMBER

NCT04754152.

The Causal Relationship between Genetically Predicted Biological Aging, Alzheimer's Disease and Cognitive Function: A Mendelian Randomisation Study

Aging is one of the most important risk factors for Alzheimer's disease (AD). Biological aging is a better indicator of the body's functional state than age (chronological aging). Leukocyte telomere length (LTL) and epigenetic clocks constructed from DNA methylation patterns have emerged as reliable markers of biological aging. Recent studies have shown that it may be possible to slow down or even reverse biological aging, offering promising prospects for treating AD. Several observational studies have reported an association between biological aging, AD, and cognitive function, but the causality behind this association and the effects of different biological aging markers on AD risk and cognitive function remain unclear. Therefore, we explored the causal relationship between them by Mendelian randomization (MR) study. Inverse-variance weighted (IVW) method is the most dominant analytical method in MR studies, which is a weighted average of estimates from different genotype combinations, and this weighted average provides an overall estimate of the causal effect. The results of the IVW analyses showed that HannumAge acceleration and LTL shortening were able to increase the risk of late-onset AD (LOAD), but not early-onset AD (EOAD). Excellent prospective memory and fluid intelligence are potentially protective against GrimAge acceleration. GrimAge acceleration and HorvathAge acceleration increase the risk of LOAD through effects on LTL. Our findings provide important insights into the role of biological aging in the pathogenesis of AD, while also highlighting the interplay of different biological aging markers and their complexity in different AD subtypes.