👤 Badri Vardarajan

Using longitudinal data from multiple cohorts, we evaluated plasma P-tau217 as a predictor of when cognitive impairment occurs in AD. P-tau217 concentrations were analyzed as continuous and binary variables using cohort-specific biomarker positivity thresholds. Association of plasma P-tau217 with prevalent and incident cognitive impairment were assessed using logistic regression and Cox models, stratified by Elevated P-tau217 levels were significantly associated with the onset of cognitive impairment. Among Plasma P-tau217 levels and the presence Show less

Epigenetic clocks associate with neuropathology and Alzheimer's disease (AD) clinical risk, but findings are mixed regarding whether clocks associate with blood-based biomarkers and in non-European populations. We calculated biological age and age acceleration from blood methylation data in 704 older Hispanic adults and tested associations with clinical diagnosis and antemortem biomarker levels. Age acceleration was significantly associated with sex, clinical diagnosis, and levels of eight plasma biomarkers, including P-tau217 levels. Additionally, biomarker associations trended more significantly among APOE-ε4 non-carriers. We also identified that methylation levels in CD4 and CD8 T-cell types are associated with age acceleration. We demonstrated that biological age acceleration, measured in blood, in a Hispanic cohort enriched for preclinical individuals, can stratify clinical AD risk and is associated with plasma AD biomarker levels. Blood-based aging clocks associate with Alzheimer's disease plasma biomarker levels. Biological aging appears relevant to pathological aging in apolipoprotein E (APOE) -ε4 non-carriers. Immune T-cell composition relates to biological aging. Show less

"SuperAgers" are oldest-old adults (ages 80+) whose memory performance more closely resembles middle-aged adults. The present study examined apolipoprotein E (APOE) allele frequency in non-Hispanic Black (NHB) and non-Hispanic White (NHW) SuperAgers compared to controls and Alzheimer's disease dementia cases. In 18,080 participants from eight cohorts, harmonized clinical diagnostics and memory, executive function, and language domain scores were used to identify SuperAgers, cases, and controls across age-defined bins. NHW SuperAgers had significantly lower frequency of APOE-ε4 alleles and higher frequency of APOE-ε2 alleles compared to all cases and controls, including oldest-old controls. Similar patterns were found in a small yet substantial sample of NHB SuperAgers; however, not all comparisons with controls reached significance. We demonstrated strong evidence that APOE allele frequency relates to SuperAger status. Further research is needed with a larger sample of NHB SuperAgers to determine if mechanisms conferring cognitive resilience differ across race groups. Apolipoprotein E (APOE) allele frequency differs between SuperAgers and cases APOE allele frequency differs between non-Hispanic White SuperAgers and controls The relationship of APOE and non-Hispanic Black SuperAger status is unclear. Show less

Circulating metabolites can identify biochemical risk factors related to Alzheimer's disease (AD). We measured plasma metabolites in 1,068 participants of Caribbean Hispanic ancestry (250 patients with AD and 818 healthy controls) across 2 cohorts and analyzed their relationship with clinical AD, biomarker-supported AD and plasma biomarkers (P-tau181, P-tau217, P-tau231 and Aβ42:Aβ40). Amino acid metabolism pathways were enriched among metabolites associated with P-tau biomarkers, whereas sialic acid and N-glycan pathways were associated with Aβ42:Aβ40. Through several dimensionality reduction approaches, we identified an APOE-ε4 dependent relationship between lysophosphatidylcholines (lysoPCs) carrying polyunsaturated fatty acids and biomarker-supported AD and P-tau biomarkers. In an independent dataset of 110 postmortem brain tissues from non-Hispanic white participants, lysoPCs in the brain were also associated with AD neuropathological features. Our results show that biomarker-based diagnostic criteria identified an APOE-ε4 dependent association with lysoPCs, which play a critical role in the transport of neuroprotective polyunsaturated fatty acids into the brain, and AD. Show less

New methods estimate amyloid positivity onset age (EAOA) from amyloid positron emission tomography (PET). We explore the genetics of EAOA to identify molecular factors underlying the earliest Alzheimer's disease (AD) changes. Harmonized amyloid PET data from 4216 participants were used in genome-wide survival, tissue-specific gene expression, and genetic covariance analyses of EAOA. Variants in apolipoprotein E (APOE), ABCA7, and RASGEF1C associated with earlier EAOA. APOE ε4/ε4 and ε3/ε4 converted 6.3 and 5 years earlier than ε3/ε3, respectively. ε2 was protective against earlier EAOA. rs4147929, an expression quantitative trait locus for ABCA7, associated with a 4 year earlier EAOA. This variant was associated with lower brain expression of ABCA7, which was associated with increased amyloid pathology at autopsy. Multiple immune-related diseases shared genetic covariance with EAOA. APOE, ABCA7, and RASGEF1C associated with earlier EAOA, with supporting evidence from tissue-specific expression analyses, offering insights into intervenable targets at early stages of AD. Novel methods estimate how long ago a patient converted to amyloid positivity. Estimating this amyloid clock allows us to determine the onset of the earliest Alzheimer's disease changes. We evaluated what genes influence when someone converts to amyloid positivity. Apolipoprotein E (APOE), ABCA7, and RASGEF1C associated with earlier age of amyloid positivity. Genetic results were supported by tissue-specific expression analyses. Show less

Core 1 biomarkers, such as amyloid positron emission tomography, capture the earliest biological changes leading to Alzheimer's disease (AD). While APOE is a major genetic factor, the contribution of other variants to Core 1 biomarkers remains unclear. The goal of this study was to determine whether genetic regulators of Core 1 biomarker levels predicted AD pathology better than genetic regulators of clinical AD. Among 955 non-Hispanic White individuals, polygenic scores (PGSs) were built using genome-wide association studies (GWASs) of amyloid PET, plasma tau phosphorylated at threonine 181 (p-tau181), cerebrospinal fluid (CSF) p-tau181, and clinical AD. Hispanic-specific PGSs were constructed in 515 individuals using plasma p-tau181 and clinical AD GWASs. Baseline and longitudinal associations with plasma biomarkers and cognition were assessed, and replication was conducted in separate cohorts. The Core 1 biomarker PGSs predicted AD pathology and associated cognitive performance better than the AD PGSs in both populations. The Core 1 PGSs show improved predictive value for AD-related plasma biomarkers and early cognitive changes. APOE ε4 explained more variance in plasma p-tau217 than in plasma p-tau181. PGSs based on Core 1 biomarkers outperformed AD PGSs in predicting plasma biomarkers and cognitive decline among asymptomatic individuals in non-Hispanic White and Hispanic individuals. However, the improvement in predictive power was modest and may vary by age. While the variance in p-tau181 and p-tau217 explained by individual Core 1 PGSs remains limited, the distinct genetic signals captured by the best-performing PGSs across different Core 1 biomarkers may provide an opportunity for developing an integrative Core 1 PGS that more effectively predicts plasma p-tau181 and p-tau217 levels than AD-based PGS. Show less

The most common form of neuronal ceroid lipofuscinosis (NCL) is juvenile CLN3 disease (JNCL), a currently incurable neurodegenerative disorder caused by mutations in the CLN3 gene. Based on our previous work and on the premise that CLN3 affects the trafficking of the cation-independent mannose-6 phosphate receptor and its ligand NPC2, we hypothesised that dysfunction of CLN3 leads to the aberrant accumulation of cholesterol in the late endosomes/lysosomes (LE/Lys) of JNCL patients' brains. An immunopurification strategy was used to isolate intact LE/Lys from frozen autopsy brain samples. LE/Lys isolated from samples of JNCL patients were compared with age-matched unaffected controls and Niemann-Pick Type C (NPC) disease patients. Indeed, mutations in NPC1 or NPC2 result in the accumulation of cholesterol in LE/Lys of NPC disease samples, thus providing a positive control. The lipid and protein content of LE/Lys was then analysed using lipidomics and proteomics, respectively. Lipid and protein profiles of LE/Lys isolated from JNCL patients were profoundly altered compared to controls. Importantly, cholesterol accumulated in LE/Lys of JNCL samples to a comparable extent than in NPC samples. Lipid profiles of LE/Lys were similar in JNCL and NPC patients, except for levels of bis(monoacylglycero)phosphate (BMP). Protein profiles detected in LE/Lys of JNCL and NPC patients appeared identical, except for levels of NPC1. Our results support that JNCL is a lysosomal cholesterol storage disorder. Our findings also support that JNCL and NPC disease share pathogenic pathways leading to aberrant lysosomal accumulation of lipids and proteins, and thus suggest that the treatments available for NPC disease may be beneficial to JNCL patients. This work opens new avenues for further mechanistic studies in model systems of JNCL and possible therapeutic interventions for this disorder. San Francisco Foundation. Show less

In a whole-exome sequencing study of multiplex Alzheimer's disease (AD) families, we investigated three neuronal ceroid lipofuscinosis genes that have been linked to retromer, an intracellular trafficking pathway associated with AD: ceroid lipofuscinosis 3 (CLN3), ceroid lipofuscinosis 5 (CLN5), and cathepsin D (CTSD). We identified a missense variant in CLN5 c.A959G (p.Asn320Ser) that segregated with AD. We find that this variant causes glycosylation defects in the expressed protein, which causes it to be retained in the endoplasmic reticulum with reduced delivery to the endolysosomal compartment, CLN5's normal cellular location. The AD-associated CLN5 variant is shown here to reduce the normal processing of cathepsin D and to decrease levels of full-length amyloid precursor protein (APP), suggestive of a defect in retromer-dependent trafficking. Show less