Algeciras‐Schimnich, Alicia

Abstract Background Plasma neurofilament light chains (NfL) and glial fibrillary acidic protein (GFAP) are blood‐based biomarkers of axonal injury and astrocytic activation, respectively, that are elevated in those with Alzheimer's disease (AD) and mild cognitive impairment (MCI) relative to cognitively unimpaired (CU) individuals. Neurite orientation dispersion and density imaging (NODDI) is a multishell diffusion MRI method capable of evaluating tissue microstructure at the axonal and dendritic level. We evaluated associations between temporal cortex orientation dispersion index (ODI), neurite density index (NDI) and isotropic volume fraction (ISOVF) and plasma NfL and GFAP concentrations. Method We included Mayo Clinic Study of Aging (MCSA) participants (ages 60‐95 years) with diagnoses or CU ( n = 356) or MCI ( n = 60), and Alzheimer's Dementia Research Center (ADRC) participants with dementia ( n = 51). NODDI imaging was obtained on a 3T Siemens Prisma scanner with 2 mm isotropic resolution. NfL and GFAP were measured using the Simoa® Neurology 4‐Plex E Advantage kit. We fit separate linear regression models within each MCALT_ADIR122 cortical ROI with regional NODDI as the primary predictor and log‐transformed plasma concentration as the outcome. Models were adjusted for age, sex, BMI, cortical thickness (or hippocampal & amygdalar volume) and total intracranial volume. Result The Table displays demographic data. Figures 1 and 2 show the relationship of NDI and ISOVF measures to plasma NfL concentrations across participants in individual ROIs (similar findings were noted with GFAP). A significant inverse relationship between NfL concentrations and NDI was observed in hippocampus, amygdala, entorhinal cortex, parahippocampal gyrus as well as all temporal neocortical regions except the superior temporal gyrus ( p <0.001) (Figure 1), whereas higher NfL concentrations were associated with higher ISOVF in all regions ( p <0.001) (Figure 2). Fewer significant associations were also seen with ODI. After adjusting for age, cortical thickness/volume and other confounds, significant associations with NDI remain, particularly in hippocampal and amygdalar regions. Conclusion NODDI‐derived measures (NDI and ISOVF) within the temporal lobe cortical regions demonstrate significant associations with plasma biomarkers of axonal and astrocytic dysfunction that are elevated during cognitive decline. This association provides preliminary validation of the utility of NODDI in assessing cortical microstructural changes associated with cognitive decline.

Abstract Background Decreased kidney function, indicated by a lower estimated glomerular filtration rate (eGFR), may affect interpretation of Alzheimer's disease (AD) blood biomarkers, including phosphorylated tau ( p ‐tau) and amyloid‐beta (Aβ) peptides, due to altered clearance. However, there is limited data available to determine the influence of eGFR on these biomarkers and whether it differs by biomarker or assay type, especially in racially diverse studies of community‐based older adults. Methods We used data from 557 participants in the Mayo Clinic Study of Aging (Rochester, MN n = 182; age 79±8 years; 36.3% Female, White participants) and the UMMC MIND Center‐Mayo Clinic Study of Aging (Jackson, MS n = 375; age 69±8 years; 73% Female 27% Black participants). eGFR was determined using the 2021 CKD‐EPI Creatinine equation. Plasma biomarkers were measured using the Lumipulse immunoassays for p ‐tau217, Aβ42, and Aβ40 (Fujirebio Diagnostics; n = 420); or the mass spectrometry‐based PrecivityAD2 assay (C2N Diagnostics; n = 253) for p ‐tau217, np‐tau217, Aβ42, and Aβ40. Common ratio values were calculated. Aβ42/40 measures were inverted so higher values are worse for all biomarkers. Log base‐2 transformed regression analysis related eGFR to each single analyte and ratio; coefficients (95% CI) reflect estimated doubling in biomarker per doubling in eGFR. Group specific [MN White ( n = 182), MS White ( n = 224), MS Black ( n = 151) participants] estimates are reported, as the distribution of social determinants of health can vary across populations and locations. Results Lower eGFR was associated with higher (worse) AD‐plasma biomarkers, and group stratified estimates were mostly consistent (Figure 1). Ratios of biomarkers diminished but did not entirely alleviate associations with eGFR. For example, MN White participants’ C2N p ‐tau217 association of ‐1.47 (‐1.94, ‐1.00), was attenuated to ‐0.67 (‐1.11, ‐0.22), when using p ‐tau217/np‐tau217. Conclusions Kidney function may be associated with AD‐plasma biomarker values, even with common ratio corrections. There was not strong evidence for highly differential associations of eGFR by race/site categories, though sample sizes are currently limited. The implications for diagnosis and risk classification need to be explored further to support health equity. Optimal consideration of comorbidities on blood biomarker concentrations must continue to be informed by investigation in large, racially and ethnically diverse, community‐based studies.

Abstract Background Plasma p ‐tau217 represents a promising alternative to PET‐ and CSF‐based biomarkers of AD in well‐characterized research cohorts. However, the performance of this accessible biomarker in outpatient clinics comprised of patients with multiple causes of cognitive impairment has yet to be established. Method Plasma Aβ42/40 and p ‐tau217 concentrations were measured using Fujirebio Lumipulse assays in patients evaluated within a subspecialty memory clinic at Mayo Clinic in Florida. Syndromic and etiologic diagnoses were established by consensus, integrating clinical data and findings from MRI ( n = 484), FDG‐PET ( n = 117), and CSF AD biomarkers ( n = 440). Plasma biomarker performance was evaluated using established diagnostic cutpoints to identify patients with “positive/elevated”, “intermediate”, or “negligible” levels of cerebral amyloid pathology on amyloid‐PET. Result Plasma AD biomarkers were measured in 509 patients (mean 68.6±9.3 years; 47% female; 91.3% non‐Hispanic White), including patients with typical amnestic AD ( n = 237, 46.6%), non‐amnestic presentations of AD ( n = 48, 9.4%), and non‐AD causes of cognitive concerns ( n = 224, 44.0%). “Intermediate” plasma p ‐tau217 and p ‐tau217/Aβ42 concentrations were reported in <15% of patients (43% of patients with Aβ42/40), implying the need for further testing to inform the likelihood of AD neuropathologic change in these patients. After excluding these patients, plasma p ‐tau217 reliably distinguished patients with symptomatic AD with 95% sensitivity and 82% specificity. Integration of Aβ42 measures (ptau217/Aβ42) incrementally improved specificity (86%). Diagnostic performance was unaffected by age (> vs < 65‐years). Plasma p ‐tau217 (AUC: 0.94; 95%CI: 0.91‐0.96) and p ‐tau217/Aβ42 performance (AUC: 0.96; 95%CI: 0.94‐0.98) were closely aligned with results of established CSF AD biomarkers ( p ‐tau181/Aβ42), outperforming Aβ42/40 (AUC: 0.78; 95%CI: 0.74‐0.83). Reduced kidney function was associated with elevated plasma p ‐tau217 and p ‐tau217/Aβ42 concentrations in patients without AD (referencing CSF AD biomarkers). Conclusion Concentrations of plasma p ‐tau217, but not Aβ42/40, strongly associated with clinical diagnoses of symptomatic AD and CSF AD biomarker results. Integration of Aβ42 measures yielded marginal improvements in performance, with increased complexity and cost. These findings support the use of plasma p ‐tau217 in heterogeneous clinical cohorts, including patients with multiple causes of cognitive impairment. Caution is advised when interpreting p ‐tau217 concentrations in patients with decreased kidney function, due to potential elevations in plasma biomarker concentrations.

Abstract Background Black and Latino Americans experience a disparate dementia burden yet remain underrepresented in dementia research, including clinical trials designed to slow or prevent symptomatic Alzheimer's disease (AD). Accessible and non‐invasive AD blood biomarkers may improve identification and recruitment of underrepresented participants into AD clinical trials. There is a clear need to assess the performance of emergent plasma AD biomarkers for the detection of AD neuropathology in cognitively normal Black and Latino Americans. Method Cognitively normal Black and Latino participants underwent cognitive evaluations and PET (amyloid‐PiB, tau‐flortaucipir) imaging at Mayo Clinic in Florida. Plasma p ‐tau217 was measured using Fujirebio Lumipulse assays. We evaluated the diagnostic performance of a p ‐tau217 threshold (≥0.186 pg/mL) known to identify non‐Hispanic White participants with cognitive impairment and “positive” amyloid PET scans (>25 Centiloids). Next, we derived an optimized threshold to identify participants with “positive” amyloid PET using Youden's method. Result The cohort included 58 Black (55%) and 47 Latino‐White (45%) well‐educated (mean 16.1±2.3 years) individuals, with mean age 64.7±8.8 years, and slight female bias (63%). Plasma p ‐tau217 concentrations increased with age (rho=0.269, p = 0.004) and declined with MoCA scores (rho=‐0.225, p = 0.027). Sixty‐nine participants completed amyloid‐ and tau‐PET imaging. Plasma p ‐tau217 concentrations increased with amyloid‐ (rho=0.254, p = 0.044) but not with tau‐PET standardized uptake value ratio (rho=0.127; p = 0.334). p ‐tau217 concentrations were ≥0.186 pg/mL in 10/69 participants (14%), including 3/3 amyloid‐ and tau‐PET positive (A+T+) participants, 3/8 A+T‐ participants (sensitivity: 55%), and 4/58 A‐T‐ participants (specificity 93%). An optimized p ‐tau217 threshold of ≥0.118 pg/mL identified 10/11 A+T± participants (sensitivity 91%), and 16/58 A‐T‐ participants (specificity 73%). In A‐T‐ participants, estimated glomerular filtration rate was lower in participants with ‘false positive’ elevations in plasma p ‐tau217 (mean difference: 67 vs 81 ml/min/1.73m 2 , p = 0.004), emphasizing the need for caution when interpreting plasma p ‐tau217 concentrations in patients with decreased kidney function. Conclusion Plasma p ‐tau217 thresholds validated in participants with symptomatic AD (≥0.186 pg/mL) failed to identify early AD neuropathology in 5/8 cognitively normal Black and Latino participants. Optimized thresholds are required to improve detection of preclinical AD in Black/Latino individuals.

Abstract INTRODUCTION Plasma phosphorylated tau at threonine 217 (p‐tau217) has emerged as one of the most promising blood‐based biomarkers for Alzheimer's disease (AD). While rare, heterophilic antibodies (HAb) are a persistent potential confounding factor in immunoassays. METHODS Potential HAb interference in the Lumipulse G pTau217 assay in samples exhibiting concentrations > 10 pg/mL were investigated. Samples were subjected to HAb blocking reagent (HBT), and in some cases, polyethylene glycol (PEG) precipitation and serial dilutions. RESULTS In 14 of the 15 suspected HAb cases, HBT treatment greatly reduced measured p‐tau217 concentrations. and in one of three specimens selected for further investigation, reduced Aβ42 concentrations PEG precipitation in the three selected samples also reduced p‐tau217 concentrations, while serial dilution yielded mixed effects. Control specimens were unaffected by sample treatment or dilutions. DISCUSSION HAb may result in falsely elevated p‐tau217 and p‐tau217/Aβ42 ratio. HAb interference should be considered in cases of unusually high p‐tau217 concentrations prior to clinical interpretation. Highlights Potential heterophile antibody (HAb) interference in the Lumipulse p‐tau217 immunoassay was investigated. Investigation was performed using HAb blocking reagent, and in some cases also using PEG precipitation . Patients with p‐tau217 concentrations > 10 pg/mL exhibited positive HAb interference in 14 of 15 cases. HAb interference can lead to falsely positive p‐tau217/Aβ42 ratios.

Abstract Background The polymorphic APOE gene is a susceptibility gene for Alzheimer's disease (AD). The ε4 allele is associated with increased risk for AD, particularly late‐onset disease, in a dose‐dependent manner. Additionally, homozygous ε4/ε4 individuals have increased risk of adverse events when undergoing amyloid lowering treatments. APOE genotyping is considered the gold standard for determination of ApoE4 zygosity. Recently, proteotype assays for ApoE4 have become available for high‐throughput immunoassay analyzers. These assays utilize the same specimen type as AD blood biomarkers and can potentially offer improved turnaround times compared to genotyping. In this study, we compare the performance of two automated ApoE4 proteotype research use only (RUO) immunoassays against APOE genotyping. Method EDTA‐plasma samples ( n = 65) from individuals undergoing ApoE PCR‐based genotyping for clinical purposes were evaluated. Samples were tested with the Beckman Coulter APOE ε4 RUO assay on the Access 2 and DXI 9000 instruments (Beckman Coulter, Inc), which provides algorithm calculated results for determining ApoE4 zygosity. Manufacturer generated data from 300 genotyped samples was used to calculate estimated cut‐points for ApoE4 zygosity for this study with results <0.55 classified as no E4, ≥0.55 to <4.55 as heterozygous E4, and ≥4.55 as homozygous E4. Samples were also tested with the Lumipulse G ApoE4 and Pan‐ApoE RUO assays on the Fujirebio Lumipulse G1200 analyzer. The ratio of ApoE4/Pan‐ApoE was utilized for determining zygosity with results <5% classified as no E4, ≥5% to <75% as heterozygous E4, and ≥75% as homozygous E4, as listed in the manufacturer IFU. Result APOE genotype distributions were (n, %): ε3ε4 (30, 46%), ε3ε3 (18, 28%), ε4ε4 (12, 18%), ε2ε3 (3, 5%), ε2ε4 (2, 3%). ApoE4 zygosity was categorized as no ε4 (21, 32%), heterozygous ε4 (32, 49%), or homozygous ε4 (12, 19%). The Beckman Coulter APOE ε4 RUO assay classified 65/65 (100%) patients correctly using manufacturer generated cut‐points on both instruments. The Lumipulse G ApoE4 and Pan‐ApoE RUO assays classified 61/65 (94%) patients correctly using the manufacturer listed cut‐points. Conclusion ApoE4 proteotype immunoassays may represent simplified and more accessible testing alternatives to genotyping for the assessment of ApoE4 zygosity in individuals being considered for amyloid lowering treatments.

Abstract Background Clinicians’ views on clinical readiness of Alzheimer's disease (AD) blood biomarkers (BBM) are not well understood. Method The Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment Biofluid‐Based Biomarkers Professional Interest Area conducted a survey to elicit clinician opinions on AD BBM implementation, including contexts of use, assay selection, reporting and result interpretation. Result Clinician respondents ( n = 212) practiced in Europe (56%), North America (24%), Caribbean and Central or South America (11%) and other continents (9%). Most respondents were medical doctors (80%) practicing in secondary or tertiary care (88%) (Table 1). For 56% of respondents, CSF AD biomarkers or amyloid PET were accessible, but 48% agreed and 52% disagreed with implementation of AD BBM in any clinical context (Table 2). Respondents emphasized the need for data from diverse populations and educational resources to support test interpretation. Conclusion Surveyed clinicians generally agreed with published appropriate use recommendations but were divided on AD BBM readiness for clinical use.

Abstract Background Chronic kidney disease (CKD) is associated with increased blood‐based biomarker concentrations, potentially confounding their utility in Alzheimer's disease (AD) evaluation. While plasma phosphorylated tau217 ( p ‐tau217) is elevated in the presence of amyloid related pathology, amyloid beta 1‐42 (Aβ42) is decreased. We investigated the association of plasma p ‐tau217, non‐phosphorylated tau217 (np‐tau217), Aβ42, Aβ40, as well as the Aβ42/Aβ40 and p ‐tau217/Aβ42 ratios, versus decreased estimated glomerular filtration rate (eGFR in mL/min/1.73 m 2 ) in individuals without amyloid pathology. Method This study included participants with CKD stages 1‐2 (eGFR 60‐98, n = 50), and stages 3‐4 (eGFR 25‐59, n = 33), who were Pittsburgh 11 C‐Compound B amyloid‐PET negative (Centiloid of < 25). Plasma p ‐tau217, np‐tau217, Aβ42, and Aβ40 were measured by immunoprecipitation mass spectrometry (C 2 N Diagnostics). %p‐tau217 [( p ‐tau217/np‐tau217) x100], Aβ42/Aβ40 ratio, and p ‐tau217/Aβ42 ratio were calculated. Log‐Log (power function) best‐fit regression analysis was used to quantitatively predict effects of changes in eGFR (2021 CKD‐EPI equation) versus each single analyte or ratio (Figure 1). Result Selected best‐fit analyte equations versus eGFR are shown in Table 1. The predicted percent increase of p ‐tau217 as eGFR decreases from 60 to 45 was 52% (95% CI: 30–78%). Significantly smaller increases of 16% were predicted for Aβ42 (95% CI: 12–21%), and 19% for Aβ40 (95% CI: 16–23%) over the same eGFR range. The best‐fit predicted increase for the p ‐tau217/Aβ42 ratio and %p‐tau217 as eGFR decreases from 60 to 45 was 31% (95% CI: 12–53%), and 19% (95% CI: 2–38%), respectively. While not recommended for assessment of amyloid pathology, the Aβ42/Aβ40 ratio did not exhibit a predicted increase (‐2.3% decrease, 95% CI: ‐5.2–0.6%) versus decreasing eGFR from 60 to 45. Conclusion The use of either %p‐tau217 or the p ‐tau217/Aβ42 ratio (to a lesser degree) reduced the confounding effects of decreasing eGFR as compared to p ‐tau217 alone. Aβ42 and Aβ40 exhibited similar reduced predicted increases versus decreasing eGFR as compared to p ‐tau217. Relative to the predicted effects of decreasing eGFR on p ‐tau217 measurements, the p ‐tau217/Aβ42 ratio relative increase was reduced by 40%, while the relative increase was reduced by 63% for %p‐tau217 measurements.

Abstract Background The quantification of Neurofilament Light chain (NfL) in blood and cerebrospinal fluid (CSF) has proven valuable for diagnosing and prognosing various neurological disorders, including Alzheimer's disease, frontotemporal dementia, amyotrophic lateral sclerosis, parkinsonism, multiple sclerosis, and ischemic damage. However, there is considerable variability in clinical and laboratory practices between centers, primarily due to different contexts of use (COU), analytical methods, and the application of cutoffs or scales. Additionally, for the same biochemical profile, the interpretation and reporting of results may vary from one center to another, raising concerns about the commutability of the tests. To date, no consensus has been reached among laboratories to define the most appropriate use of cutoffs or conclusions/comments based on NfL profiles. Method This international project involves 38 laboratories across 18 countries, all specialized in the biochemical diagnosis of neurological disorders. Using a questionnaire, we obtained descriptions from each center regarding their COU, pre‐analytical and analytical protocols (including the biological fluid and methods used to quantify NfL). Through a consensus approach, we developed a harmonized strategy for the use and reporting of NfL results across different centres according to their respective COU. Results Among the centers, 63% quantified NfL in the CSF, 87% in blood and 53% in both fluids. COU were as follow: frontotemporal dementia (71%), Alzheimer disease (71%), multiple sclerosis (61%), amyotrophic lateral sclerosis (61%), psychiatric syndrome (45%), Creutzfeldt‐Jakob disease (32%), Parkinson disease (39%), peripheral neuropathy (29%), traumatic brain injury (21%), Huntington's disease (13%), amyloid transthyretin related (11%) and cardiac arrest (8%). Most of the centers define pathological cutoffs based on publications (50%) and take age into account for this purpose (42%). Reporting is mostly transmitted through numeric results (95%). Conclusion Harmonizing cutoffs, reporting, and interpretation across various clinical contexts will facilitate the incorporation of this biomarker into routine clinical practice.

Abstract Background Clinically available plasma p ‐tau217 assays may be utilized in the determination of eligibility for amyloid‐lowering therapies. Our institution recently introduced a plasma p ‐tau217 assay in clinical practice using a two‐cutpoint approach that optimizes the accuracy while minimizing false positive risk and categorizing ≤20% of results as intermediate. In this study, we prospectively evaluate the performance of a plasma p ‐tau217 assay for detection of amyloid pathology using these predefined cutpoints. Method Patients recruited were being considered for lecanemab therapy at a tertiary care subspecialty clinic. Plasma p ‐tau217 was measured using the clinically available Fujirebio Lumipulse p ‐tau217 assay at Mayo Clinic, and results (pg/mL) were classified as either negative (≤0.185), intermediate (0.186–0.324) or positive (≥0.325). Amyloid pathology was determined by amyloid‐PET and/or CSF p ‐tau181/Aβ42. Result Ninety‐three patients were recruited between November 2023 and December 2024. Of these, 49 underwent amyloid‐PET, 4 had CSF p ‐tau181/Aβ42 measurements, and 40 had both PET and CSF results (with 3/40 discordant cases), for use in the assessment of amyloid pathology. The three discordant cases were considered amyloid positive for purposes of plasma p ‐tau217 comparison. Overall amyloid positivity was 90%. Plasma p ‐tau217 results were positive in 83% (77/93), negative in 6% (6/93), and intermediate in 11% (10/93) of patients. An elevated p ‐tau217 predicted the presence of amyloid positivity with a diagnostic accuracy of 96% (95% CI 90% − 99%). In the intermediate range, 80% of patients were positive for amyloid pathology. In patients with a definitive p ‐tau217 result (positive or negative), the positive and negative predictive values were 97% and 83%. There were three patients with discordant results: one PET+/p‐tau217‐, one PET‐/p‐tau217+, and one CSF‐/p‐tau217+. Clinical presentation of these discordant cases was examined, and relevant findings will be discussed. Conclusion The Lumipulse plasma p ‐tau217 assay exhibited acceptable diagnostic accuracy for the determination of amyloid pathology when compared to either amyloid‐PET or CSF p ‐tau181/Aβ42. This prospective study confirms the utility a two‐cutpoint approach for interpreting plasma p ‐tau217 for the assessment of amyloid pathology eligibility for amyloid‐lowering therapies in a heterogenous clinical cohort.