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Abstract INTRODUCTION The genetic basis of sporadic early‐onset Alzheimer's disease (EOAD) remains largely unknown, prompting evaluation of late‐onset Alzheimer's disease (LOAD) polygenic risk in EOAD. METHODS A LOAD polygenic score (PGS) was calculated in the Longitudinal Early‐onset Alzheimer's Disease Study (LEADS) and Alzheimer's Disease Neuroimaging Initiative (ADNI) study and tested for associations with AD risk, cognitive performance, and imaging and fluid biomarkers. RESULTS Though PGS was elevated in LOAD and EOAD, it was not a significant predictor of EOAD adjusting for APOE ε4 carrier status and was not associated with age of EOAD onset ( p = 0.106) or with cognitive performance ( p = 0.417). In LEADS, greater LOAD PGS was associated with differences in neuroimaging and fluid biomarkers, including elevated synaptosomal‐associated protein 25 (SNAP‐25) ( p = 2.3 × 10 −5 ). DISCUSSION While LOAD polygenic risk contributed minimally to EOAD onset and cognitive dysfunction, PGS association with fluid biomarkers in LEADS suggests a role for LOAD polygenic risk in EOAD pathophysiology. Highlights LOAD PGSs were elevated in both LOAD and EOAD compared to controls; however, LOAD PGS did not significantly predict EOAD risk, age at onset, or cognitive performance independent of APOE ε4 in the LEADS. Higher LOAD PGS was associated with lower amyloid PET Centiloids (less brain amyloid deposition) as well as lower CSF biomarker Aβ42 in LEADS (proxy marker suggesting higher brain amyloid deposition) in LEADS; these contradictory findings support the need for larger studies to further investigate whether LOAD PGS is associated with increased amyloid deposition in EOAD. Higher LOAD PGS was also associated with higher levels of CSF synaptosomal‐associated protein 25 (SNAP‐25), a key component of the SNARE complex, suggesting that LOAD genetic factors may contribute to dysregulation of synaptic transmission and/or pathological protein aggregation in EOAD.

Abstract Background Chimeric antigen receptor T-cell therapy (CAR-T) has transformed care for relapsed or refractory B-cell malignancies. Cytokine-release syndrome (CRS) complicates most infusions, yet the ensuing infection risk is ill-defined.Table 1Profile of 230 patients undergoing with CRS following CAR-T therapyTable 2Cytokine Release Syndrome Severity, Management, and Early Outcomes by 90-Day Infection Status Methods CAR-T recipients who developed CRS at our institution from 1 Jan 2018 to 3 June 2024 were retrospectively reviewed. Variables were abstracted into REDCap. CRS was graded with American Society for Transplantation and Cellular Therapy (ASTCT) criteria. All infections occuring after CRS onset to day 90 were adjudicated. Continuous data are reported as medians with interquartile ranges (IQR); categorical data as counts and percentages. Table 2 comparisons used Mann-Whitney U for continuous and χ² or Fisher exact tests for categorical variables (two sided, P < 0.05). Multivariable logistic regression was used to identify independent predictors of infection.Table 3Infectious Syndromes, Pathogens, and Timing of First Infection Following CRS Onset Results Among 230 CRS cases, median age was 64 yr (IQR 57–70) and 59% were male. Non-Hodgkin lymphoma accounted for 62% and multiple myeloma for 38%. Median prior therapy lines were 3. CRS was grade 1–2 in 97%. CAR-HEMATOTOX was low in 156 (68%) (Table 1). Within 90 days, 51 patients (22%) developed infection; median onset was 15 days (IQR 5–26). Infected patients more often received anakinra (22% vs 8%, p = 0.02) and required ICU care (18% vs 7%, p = 0.05); grade ≥3 CRS trended higher (10% vs 3%, p = 0.06). In multivariable analysis adjusting for age, CAR-HEMATOTOX, ICU admission, and anakinra, both ICU admission (aOR 2.06; 95% CI 0.70–5.81; p = 0.18) and anakinra use (aOR 2.18; 95% CI 0.83–5.53; p = 0.10) were associated with higher infection odds, though not statistically significant. 90-day survival was 88% with infection versus 96% without (p = 0.09) (Table 2). 51 infectious episodes were documented: bacteremia 22; gastrointestinal 9; central line–associated bloodstream infection 7; other sites 22. Bacteria caused 59%, viruses 37% (15 CMV, 4 SARS-CoV-2), and fungi 4%. No infection-related deaths occurred (Table 3). Conclusion Infection was common after CRS, but did not alter early survival. Anakinra exposure and ICU admission were associated with a higher likelihood of infection, though not statistically significant. Targeted surveillance should focus on patients requiring intensified CRS management. Disclosures Yi Lin, M.D., BMS: Board Member|Caribou: Advisor/Consultant|Genentech: Board Member|Jassen: Board Member|Jassen: Steering Committee|Kite/Gilead: Steering Committee|Legend: Board Member|NexImmune: Advisor/Consultant|NexT Therapeutics: Board Member|Pfizer: Board Member|Regeneron: Board Member|Sanofi: Board Member|Tessera: Board Member Paschalis Vergidis, MD, MSc, Current Fungal Infection Reports: Honoraria|F2G: Grant/Research Support|Merck Manuals: Honoraria|Mundipharma: Grant/Research Support|Scynexis: Advisor/Consultant|Scynexis: Grant/Research Support

Abstract Background Persistent candidemia (PC) occurs in a minority of Candida bloodstream infections (BSIs) but is associated with increased morbidity. Comparative data on patient profile, species distribution and outcomes are limited.Table 1Clinical profile and outcomes of patients with persistent candidemia in the primary study cohort. ANC = absolute neutrophil count. SD = standard deviation.Table 2Comparative analysis of persistent candidemia and non-persistent candidemia cases. Methods All candidemia episodes at three academic medical centers (2018-2025) were reviewed. Persistence was defined as ≥72 hours of positive blood cultures after appropriate antifungal initiation. Each PC case was matched 1:2 to non-PC controls who survived ≥72 hours. Demographics, Charlson Comorbidity Index (CCI), Candida species distribution, and outcomes were used for comparative analysis. Continuous variables were summarized as median (interquartile range [IQR]) and compared with Wilcoxon rank-sum, while categorical data (n%) were analyzed by Fisher’s exact test (species by χ²), yielding odds ratios (ORs) with 95% confidence intervals (CIs). Two-tailed p < 0.05 denoted significance. Results Each PC case (n = 46) was matched 1:2 to non-PC controls (n = 92). Clinical profiles and outcomes of PC cases are presented in Table 1. Most PC patients (54.3%) had an immunocompromising condition, and non-urinary intra-abdominal sources were the most frequently suspected infection source (21/46; 45.7%). All but one of 46 PC cases had antibiotic exposure within the preceding 90 days. Comparative demographics and outcomes for PC cases and non-PC controls are displayed in Table 2. PC patients were younger (median 62 yr, IQR 45–69 vs 68 yr, 57–76; p = 0.01), more often female (59% vs 30%; OR 3.3, 95% CI 1.5–7.1; p = 0.002), and had higher comorbidity (CCI 5, IQR 3–8 vs 3, 1–4; p < 0.001). Species distribution differed (χ² p = 0.04), driven by C. guilliermondii over-representation in PC cases (9% vs 0%) (Figures 1 and 2). Hospital stay was longer in PC cases (median 36 d, 24–54 vs 16 d, 8–28; p < 0.001) and time from admission to first culture greater (12 d, 3–26 vs 3 d, 1–10; p = 0.003). 90-day mortality was 54.3% (25/46) in PC cases versus 31.5% (29/92) in controls (OR 2.57, 95% CI 1.17–5.71; p = 0.016). Conclusion In this 7-year multicenter study, there were significant differences in demographics, microbiology, and clinical outcomes between PC and non-PC cases, including higher short-term mortality rates with PC in univariate analysis. Disclosures Paschalis Vergidis, MD, MSc, Current Fungal Infection Reports: Honoraria|F2G: Grant/Research Support|Merck Manuals: Honoraria|Mundipharma: Grant/Research Support|Scynexis: Advisor/Consultant|Scynexis: Grant/Research Support

Abstract Background Native joint septic arthritis (NJSA) is a serious musculoskeletal infection requiring timely surgical intervention to prevent long-term morbidity. Although current guidelines recommend early surgical debridement, supporting data, particularly on long-term outcomes, remain scarce. Given this, we evaluated the association between surgical timing and 1-year clinical outcomes using the Desirability of Outcome Ranking (DOOR) framework, applied for the first time in NJSA.Table 1.Desirability of Outcome Ranking (DOOR) ordinal scaleTable 2.Baseline demographic, clinical characteristics, and treatment outcomes Methods We conducted a retrospective multicenter cohort study of adults (≥18 years) with NJSA who underwent surgery across Mayo Clinic campuses between 2012 and 2021. Clinical outcomes at one year were assessed using a 9-level DOOR scale, incorporating survival, treatment failure (relapse, reinfection, readmission, or significant surgical events), and joint recovery (full vs qualified) (Table 1). Time to surgery from hospital admission was analyzed both as a continuous variable and as categories: < 1, 1–2, or ≥3 days.Table 3.Associations between duration and outcomesFigure 1.Association Between Time to Surgery and DOOR Scores in Native Joint Septic Arthritis.A) Distribution of Modified DOOR Scores by Surgical Timing. B) Modeled Probability of DOOR Scores by Time to Surgery. Results Among 268 patients (median age 62 years, 61% male), 30% underwent surgery < 1 day from admission, 47% within 1–2 days, and 24% at ≥3 days. At 1 year, 57% achieved full recovery without unfavorable events (DOOR score 1), while treatment failure occurred in 34% (Table 2). In unadjusted analyses, longer surgical delay was significantly associated with higher DOOR scores (per IQR increase [from 0 to 2 days], OR: 1.5; 95% CI: 1.0–2.1; p = 0.026) and with increased 1-year mortality (HR: 1.7; 95% CI: 1.1–2.6; p = 0.019) and treatment failure (HR: 1.5; 95% CI: 1.1–2.0; p = 0.007). Similar results were obtained when delay was used as a categorical 3-level variable, with the highest risk observed in patients undergoing surgery after ≥3 days. After adjusting for age and Charlson index, only the association between surgical delay and treatment failure remained statistically significant (HR: 1.5; 95% CI, 1.1–2.0; p=0.016) (Table 3, Figure 1). Conclusion Delayed surgical intervention for management of NJSA was independently associated with higher risk of treatment failure at 1 year. These findings reinforce current guideline recommendations for timely operative management and further underscore the potential of the DOOR framework to capture clinically meaningful, multidimensional outcomes in NJSA. Disclosures All Authors: No reported disclosures

Abstract Background Atypical clinical presentations of Alzheimer's disease (AD) are associated with heterogeneous patterns of cortical tau‐PET uptake. The medial‐temporal (MTL) meta‐ROI is typically used to determine tau‐PET abnormality in AD, but this approach may not detect focal uptake in atypical patients. Our goal was to develop regional tau‐PET cut‐points and determine whether the number of positive regions better captures positive tau‐PET signal in atypical AD. Method 127 amyloid‐positive atypical AD (visual=68, language=39, motor=15, others=5) and 62 amyloid‐negative cognitively unimpaired (CU) individuals were recruited by the Neurodegenerative Research Group, Mayo Clinic, and underwent, amyloid‐PET and 18 F‐AV‐1451(tau)‐PET. Images were parcellated using the modified Harvard‐Oxford atlas and we focused on 67 AD‐specific regions. Rather than using the average SUVR across voxels within a region to quantify uptake, we used the 95 th percentile of SUVR values across voxels within a region to capture focal cases. We then used receiver operating characteristic (ROC) methods and a Youden threshold to define regional abnormality. The number of abnormal regions was calculated for each participant and used to discriminate between CU and atypical AD at the individual level. Result Across 64 regions, our approach showed excellent (AUROC>0.90) differentiation between atypical AD and CU. The temporal‐fusiform, parahippocampal gyrus and inferior temporal gyrus showed the best differentiation (Figure 1). All 67 regions showed excellent specificity (>85%), with 63 regions showing excellent sensitivity (≥80%). The lateral occipital cortex, temporal‐fusiform and parahippocampal gyrus showed the best specificity and sensitivity (Figure 2). The distribution of the number of tau‐elevated regions is shown in Figure 3. 74% of CU had no positive regions, while 43% of the atypical AD patients had all 67 regions affected. An optimal threshold of 7 tau‐elevated regions classified all CU below, and 123 (97%) atypical AD above threshold. Using a standard approach based on the average SUVR in the MTL meta‐ROI, only 116 (91%) atypical AD patients were tau‐PET positive. Conclusion Tau uptake in temporal regions showed the greatest group‐level differentiation. However, examining regional tau‐positivity may offer better sensitivity in atypical AD patients compared to the temporal meta‐ROI, likely due to the presence of focal non‐temporal patterns of uptake.

Abstract Background The tau PET imaging with 18F‐flortacipir (18F‐FTP) has focused interest in accurately tracking longitudinal tau changes in Alzheimer's disease [1]. Thus, minimizing variability is critical. Off‐target signal has the potential to complicate interpretation of tau‐PET imaging due to potential spillover or bleed‐in effects, with increased effects seen in later stages of Alzheimer's due to cerebral atrophy and proximity of off‐target areas to relevant cortical areas[2]. Previously, we demonstrated the effect of uptake period activity on 18F‐FTP signal. With increasing recent interest in demographic factors that may affect off‐target binding, we investigated the effect of age in extra‐cerebral off‐target signal in 18F‐FTP PET imaging. Method Standard 18F‐FTP PET protocol was performed in 330 participants. Two independent readers measured tau uptake in predetermined off‐target regions, including extraocular muscle, meninges, and occipital bone among others. Linear regression models assessed the relationship between participants’ age, sex, and tau uptake values (SUV and SUVr) (SUV = (Tissue radioactivity concentration / Injected dose) / Body weight & SUVr = SUV of target region/ SUV of reference region.) Result Sex had a significant effect on off‐target signal in most brain regions, with variable positive or negative correlation based on area. Notably, SUV in the eyeball‐retina, occipital bone, upper skull meninges all showed significant positive correlation with sex, with ‘male’ status generally associated with lower SUV. The greatest effect of sex was observed in superior skull meninges, occipital bone, and internal carotid artery ( p <0.001). Age showed minimally affected SUV and SUVr in off‐target regions. SUVr values show a significant correlation with SUV values of upper skull meninges in sex. Cognitive status did not significantly affect off‐target SUV. Conclusion We observed that sex significantly affected extra‐brain off‐target signal in 18F‐FTP PET imaging, while age has minimal effect, adding to previous evidence of off‐target binding within brain regions. Further evaluation is necessary to understand the age‐related effects on off‐target regions. As a result, the variability introduced by sex may pose challenges to studying tau accumulation.

Abstract Background An intense search is underway for tau PET tracers with enhanced capability to visualize tau aggregates. Research indicates that [18F] AV1451 and [18F]MK 6240 exhibit comparable binding properties in terms of spatial distribution and severity of tau aggregates, as observed both in‐vivo and in‐vitro. This study focused on head‐to‐head pathological comparison of both the tracers binding specificity to tangle maturity levels (pretangles, mature tangles and ghost tangles) of tau aggregates as seen on autoradiography as compared to CP‐13 (early tangle maturity marker) and PHF‐1(middling tangle maturity marker) immunohistochemical (IHC) stains in Alzheimer's disease (AD) and non‐AD tauopathies. Method Study participants included included those with AD and non‐AD tauopathies. Analyses were performed on serial 5um formalin fixed paraffin embedded postmortem human brain sections acquired from Mayo clinic brain bank. Visual assessment of colocalization with IHC as well as quantitative analyses were used. IHC sections were incubated with antibodies CP‐13 (recognizing early tangle maturity) and PHF‐1 (recognizing middling tangle maturity). Result A total of 38 participants were examined. The participants included a spectrum from normal to AD, including mild cognitive impairment (MCI) and atypical AD. Participants with N279K (4R), P301L (4R), and R406W MAPT mutations (3R+4R) were included as well. Both the tracers showed strong binding to AD tau aggregates and no or minimal binding to non‐AD tauopathies. Generally, early tangle maturity tau accumulation participants had more tau demonstrated with CP‐13 than PHF‐1 and both the tracers [18F]MK 6240 and [18F]AV 1451 binding are well correlated with the PHF‐1 staining suggesting the preference for middling tangle level and minimal to early tangles. Conclusion The emergence and validation of these new tau PET tracers have opened new opportunities for the development of more accurate diagnostic and management tools for AD. In our study on post‐mortem sections, [ 18 F]MK‐6240 and [ 18 F]Flortaucipir showed similar binding profiles with preference to middling tangle maturity levels.

Abstract Background Isolated REM sleep behavior disorder (iRBD) is a parasomnia that reflects an evolving α‐synucleinopathy disorder, providing an opportunity to study early pathological changes. While diffusion tensor imaging (DTI) studies have shown white matter changes in iRBD, Neurite Orientation Dispersion and Density Imaging (NODDI) may offer better biological specificity in characterizing microstructural alterations through measures of Neurite Density Index (NDI), Orientation Dispersion Index (ODI), and Free Water Fraction (FWF). Method We included 77 participants with polysomnography‐confirmed iRBD from the North American Prodromal Synucleinopathy (NAPS) Consortium and 154 age‐ and sex‐matched cognitively unimpaired controls from the Mayo Clinic Study of Aging. White matter microstructure was evaluated using standardized multi‐shell diffusion on 3T MRI, quantifying DTI metrics (fractional anisotropy, FA; and mean diffusivity, MD) and NODDI parameters across bilateral white matter tracts defined by the JHU “Eve” WM atlas. Group differences were assessed using conditional logistic regression, with correlations to motor performance evaluated using the Purdue Pegboard and Alternating Finger Tapping tests. Result Compared to controls, iRBD participants demonstrated widespread and bidirectional white matter changes across major white matter pathways (see Figure 1 for glass brain visualizations). While predominantly showing decreases, FA exhibited some increases, particularly in the corticospinal tract. MD showed a largely opposite pattern with predominantly increased values across tracts. NODDI metrics revealed complex bidirectional patterns: ODI was broadly increased across multiple tracts with focal decreases, while NDI showed a pattern of predominantly decreased values alongside localized increases. FWF demonstrated a mixed pattern with predominant decreases across most tracts. In addition, both DTI and NODDI metrics showed extensive, moderate correlations with the Purdue Pegboard Test and Alternating Finger Tapping performance ( T = 2.0, p < 0.05, Figure 2). Conclusion Our study highlighted widespread and complex bidirectional white matter microstructural alterations in individuals with iRBD, demonstrating significant correlations with dexterity and motor performance even during the prodromal stage. These results suggest that extensive white matter abnormalities occur early in prodromal α‐synucleinopathies and highlight the value of advanced diffusion imaging techniques in characterizing iRBD and its potential prediction of phenoconversion to overt neurodegenerative disorders.

Abstract Background Amyloid related imaging abnormality edema (ARIA‐E) occurs in about 19% of individuals with autosomal dominant Alzheimer disease (ADAD) treated with an anti‐amyloid‐b monoclonal antibody (Salloway et al., 2021). In a previously reported case, ARIA‐E appeared to colocalize with decreases in PiB‐PET uptake (Joseph‐Mathurin, Llibre‐Guerra, et al, 2022), suggesting an association between amyloid‐b (Aβ) removal and ARIA‐E. Here, we compare longitudinal neuroimaging and corresponding neuropathology in an ADAD individual treated with gantenerumab, who experienced multiple ARIA‐E episodes as sulcal effusions that resolved by the end of the four‐year trial. Methods PiB‐PET and MRI were collected pre‐ and post‐randomization (2 and 4 years). The participant consented to brain donation, which was received a year after trial completion. Four tissue samples were taken from the location of the ARIA‐E in the parieto‐occipital left hemibrain as identified by MRI (one block contained the sulcus affected by ARIA‐E; the rest of the coronal section was captured in the remaining three blocks). Area fractions (AFs) of Aβ (10D5 immunohistochemistry (IHC)), tauopathy (PHF1), microglia (Iba1), and astrocytes (GFAP) in one sulcal region of interest (ROI) from each block and PiB‐PET SUVRs of corresponding ROIs were extracted ( n = 4, Figure 1). Additionally, we included PiB‐PET SUVRs corresponding to ARIA‐E findings observed in the right hemisphere at baseline, two‐year, and four‐year visits ( n = 6). Results Overall PiB‐PET uptake increased during the first two years (before ARIA‐E) and decreased during the last two years (including ARIA‐E episodes) (0.03±0.05 vs. ‐0.04±0.04 SUVR/year, p ‐value=0.01, Figure 2). The decrease seemed more pronounced in ARIA‐E ROIs versus normal‐appearing sulcus ROIs (‐0.05±0.04 vs. ‐0.02±0.03 SUVR/year). Lower PiB uptake at last visit appeared associated with lower Aβ AF (estimates=0.03±0.01, p ‐value=0.07). The ARIA‐E ROI had an Aβ AF of 0.009 while normal‐appearing sulcus ROIs had a mean of 0.02+0.003 (Figure 3). AFs for tauopathy, microglia, and astrocytes were within the range of those of normal‐appearing sulcus ROIs, suggesting an Aβ‐specific effect, although unexamined markers may play a role. Conclusions Our preliminary findings indicated that ARIA‐E is associated with longitudinal PiB‐PET decrease and Aβ AF, supporting the link between ARIA‐E, changes in PiB‐PET, and local Aβ removal observed at autopsy. Funding : K01AG080123; U01AG042791; R01AG046179; R01AG053267

Abstract Background The IWG and AA diagnostic criteria are major references in the Alzheimer's domain. Although they share analogies, some key differences should be recognized. Method The original IWG 2024 JAMA Neurology and AA 2024 Alzheimers Dement papers will be used as the major data references. Result I will outline the similarities and differences between the IWG and the AA criteria for Alzheimer's disease from the point of view of the former. I will discuss similarities regarding: Aim of clinical research on AD and other cognitive disorders, Role of co‐pathology, Role of brain reserve, Biomarker use, Indication for anti‐β‐amyloid, Contra‐indication for anti‐β‐amyloid, and Health care delivery model. I will discuss differences regarding: Core question, Scientific discourse, Knowledge source, Definition of AD, Diagnosis of AD, and Interventions for AD. Conclusion The differences between the two sets of criteria are not “just semantics”. A unified definition of AD is essential to advance the field and improve patient care.