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We describe in vivo follow-up PET imaging and postmortem findings from an autosomal dominant Alzheimer’s disease (ADAD) PSEN1 E280A carrier who was also homozygous for the APOE3 Christchurch (APOE3ch) variant and was protected against Alzheimer’s symptoms for almost three decades beyond the expected age of onset. We identified a distinct anatomical pattern of tau pathology with atypical accumulation in vivo and unusual postmortem regional distribution characterized by sparing in the frontal cortex and severe pathology in the occipital cortex. The frontal cortex and the hippocampus, less affected than the occipital cortex by tau pathology, contained Related Orphan Receptor B (RORB) positive neurons, homeostatic astrocytes and higher APOE expression. The occipital cortex, the only cortical region showing cerebral amyloid angiopathy (CAA), exhibited a distinctive chronic inflammatory microglial profile and lower APOE expression. Thus, the Christchurch variant may impact the distribution of tau pathology, modulate age at onset, severity, progression, and clinical presentation of ADAD, suggesting possible therapeutic strategies.

Autosomal dominant Alzheimer’s disease (ADAD) is genetically determined, but variability in age of symptom onset suggests additional factors may influence cognitive trajectories. Although apolipoprotein E ( APOE ) genotype and educational attainment both influence dementia onset in sporadic AD, evidence for these effects in ADAD is limited. To investigate the effects of APOE and educational attainment on age-related cognitive trajectories in ADAD, we analyzed data from 675 Presenilin-1 E280A mutation carriers and 594 non-carriers. Here we show that age-related cognitive decline is accelerated in ADAD mutation carriers who also have an APOE e4 allele compared to those who do not and delayed in mutation carriers who also have an APOE e2 allele compared to those who do not. Educational attainment is protective and moderates the effect of APOE on cognition. Despite ADAD mutation carriers being genetically determined to develop dementia, age-related cognitive decline may be influenced by other genetic and environmental factors. PSEN1 E280A carriers develop dementia by midlife, but there is variability in disease trajectory. Cognitive decline is accelerated in E280A carriers who also have an APOE e4 allele. Educational attainment moderates the effect of APOE on cognition.

Frontotemporal dementia (FTD) is one of the leading causes of young‐onset dementia before age 65, typically manifesting as abnormal behavior (in behavioral variant FTD) or language impairment (in primary progressive aphasia). Although FTD affects all populations across the globe, knowledge regarding the pathophysiology and genetics derives primarily from studies conducted in North America and Western Europe. Globally, biomedical research for FTD is hindered by variable access to diagnosis, discussed in this group's earlier article, and by reduced access to expertise, funding, and infrastructure. This perspective paper was produced by two professional interest areas of the Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment (ISTAART) and discusses the field's current status on the cross‐cultural aspects of basic and translational research in FTD (including that focused on epidemiology, genetics, biomarkers, and treatment). It subsequently provides a summary of gaps and needs to address the disparities and advance global FTD biomedical research.

INTRODUCTION While Latin America (LatAm) is facing an increasing burden of dementia due to the rapid aging of the population, it remains underrepresented in dementia research, diagnostics, and care. METHODS In 2023, the Alzheimer's Association hosted its eighth satellite symposium in Mexico, highlighting emerging dementia research, priorities, and challenges within LatAm. RESULTS Significant initiatives in the region, including intracountry support, showcased their efforts in fostering national and international collaborations; genetic studies unveiled the unique genetic admixture in LatAm; researchers conducting emerging clinical trials discussed ongoing culturally specific interventions; and the urgent need to harmonize practices and studies, improve diagnosis and care, and use affordable biomarkers in the region was highlighted. DISCUSSION The myriad of topics discussed at the 2023 AAIC satellite symposium highlighted the growing research efforts in LatAm, providing valuable insights into dementia biology, genetics, epidemiology, treatment, and care.

Background The Colombian population, as well as those in other Latin American regions, arose from a recent tri-continental admixture among Native Americans, Spanish invaders, and enslaved Africans, all of whom passed through a population bottleneck due to widespread infectious diseases that left small isolated local settlements. As a result, the current population reflects multiple founder effects derived from diverse ancestries. Methods We characterized the role of admixture and founder effects on the origination of the mutational landscape that led to neurodegenerative disorders under these historical circumstances. Genomes from 900 Colombian individuals with Alzheimer’s disease (AD) [ n = 376], frontotemporal lobar degeneration-motor neuron disease continuum (FTLD-MND) [ n = 197], early-onset dementia not otherwise specified (EOD) [ n = 73], and healthy participants [ n = 254] were analyzed. We examined their global and local ancestry proportions and screened this cohort for deleterious variants in disease-causing and risk-conferring genes. Results We identified 21 pathogenic variants in AD-FTLD related genes, and PSEN1 harbored the majority (11 pathogenic variants). Variants were identified from all three continental ancestries. TREM2 heterozygous and homozygous variants were the most common among AD risk genes (102 carriers), a point of interest because the disease risk conferred by these variants differed according to ancestry. Several gene variants that have a known association with MND in European populations had FTLD phenotypes on a Native American haplotype. Consistent with founder effects, identity by descent among carriers of the same variant was frequent. Conclusions Colombian demography with multiple mini-bottlenecks probably enhanced the detection of founder events and left a proportionally higher frequency of rare variants derived from the ancestral populations. These findings demonstrate the role of genomically defined ancestry in phenotypic disease expression, a phenotypic range of different rare mutations in the same gene, and further emphasize the importance of inclusiveness in genetic studies.

INTRODUCTION This study investigates primary lateral sclerosis (PLS) as a rare manifestation of the presenilin 1 (PSEN1) NM_000021 c.851C > T p.Pro284Leu variant in three siblings of a Colombian family, outlining its clinical and neuropathological features and their relationship to Alzheimer's disease (AD). METHODS Data were gathered using clinical evaluations, next‐generation genetic sequencing, magnetic resonance imaging, biomarker analysis, and neuropathological examination. RESULTS Carriers of the PSEN1 Pro284Leu variant exhibited classic PLS symptoms, including unilateral onset and bulbar syndromes, along with cognitive decline. Neuropathology showed corticospinal tract degeneration without amyloid beta deposition in spinal white matter. DISCUSSION Our findings suggest an overlap between PLS and AD pathology in PSEN1 variant carriers. Results support considering PLS when diagnosing AD‐related motor syndromes and including PSEN1 evaluation when performing genetic testing for PLS. The study highlights the need for further research to clarify the PLS–AD relationship, informing future treatments and clinical trials. Highlights Pathogenic variants in presenilin 1 (PSEN1) can manifest as hereditary primary lateral sclerosis PSEN1 Pro284Leu carriers present motor, cognitive, and behavioral alterations  Cases had corticospinal tract microgliosis and severe Aβ pathology in motor cortex  There was no evidence of amyloid deposition in the spinal cord white matter  All the neuropathology images are available for online visualization  Myelin pallor in the spinal cord is confined to the lateral corticospinal tracts

We identified a PSEN1 (presenilin 1) mutation carrier from the world’s largest autosomal dominant Alzheimer’s disease kindred, who did not develop mild cognitive impairment until her seventies, three decades after the expected age of clinical onset. The individual had two copies of the APOE3 Christchurch (R136S) mutation, unusually high brain amyloid levels and limited tau and neurodegenerative measurements. Our findings have implications for the role of APOE in the pathogenesis, treatment and prevention of Alzheimer’s disease.

Genome-wide association studies (GWAS) of Alzheimer’s disease are predominantly carried out in European ancestry individuals despite the known variation in genetic architecture and disease prevalence across global populations. We leveraged published GWAS summary statistics from European, East Asian, and African American populations, and an additional GWAS from a Caribbean Hispanic population using previously reported genotype data to perform the largest multi-ancestry GWAS meta-analysis of Alzheimer’s disease and related dementias to date. This method allowed us to identify two independent novel disease-associated loci on chromosome 3. We also leveraged diverse haplotype structures to fine-map nine loci with a posterior probability >0.8 and globally assessed the heterogeneity of known risk factors across populations. Additionally, we compared the generalizability of multi-ancestry- and single-ancestry-derived polygenic risk scores in a three-way admixed Colombian population. Our findings highlight the importance of multi-ancestry representation in uncovering and understanding putative factors that contribute to risk of Alzheimer’s disease and related dementias.

Studying comorbidities in early onset Alzheimer disease (AD) may provide an advantageous perspective on their pathogenesis because aging factors may be largely inoperative for these subjects. We compared AD comorbidities between early-onset sporadic cases and American and Colombian cases with PSEN1 mutations. AD neuropathological changes (ADNC) were very severe in all groups but more severe in the PSEN1 groups. Lewy body disease and cerebral white matter rarefaction were the most common (up to 60%) of AD comorbidities, followed by arteriolosclerosis (up to 37%), and large-vessel atherosclerosis (up to 20%). Differences between the 3 groups included earlier age of onset in the American PSEN1 cases, shorter disease duration in sporadic cases, and more frequent large-vessel atherosclerosis and cerebral amyloid angiopathy in the Colombian PSEN1 cases. Logistic regression models adjusted for age and sex found the presence of a PSEN1 mutation, an apolipoprotein ε4 allele and TDP-43 pathology to predict an earlier age of onset; Hispanic ethnicity and multiracial subjects were predictive of severe CAA. Comorbidities are common in early onset AD and should be considered when planning clinical trials with such subjects. However, they may be at least partially dependent on ADNC and thus potentially addressable by anti-amyloid or and/anti-tau therapies.

Background Genetic studies for Alzheimer's disease and related dementias are underrepresented in Latin America. The Multi‐Partner Consortium to Expand Dementia Research in Latin America (ReDLat) cohort recruits from ten centers in six countries across Latin America, providing an opportunity to address this shortcoming. Method 2,736 participants with available genetic material were assessed via Illumina genome sequencing. Genetic ancestry was determined via the package GenoTools and data were analyzed separately by genetic ancestry group. The largest genetic ancestry group was admixed American (AMR) with 2,147 individuals. Of these 2,147 individuals, 65 were excluded in quality control steps leaving 981 controls, 771 AD, 298 FTD, and 32 with other or indeterminate phenotypes. GWAS was conducted using GEMMA which adjusts for admixture and familial relationships using a kinship matrix. Burden analysis was also conducted with adjustment via a kinship matrix. Result In the AD GWAS, the only genome‐wide significant (p < 5x10‐8) hit in preliminary analysis was the APOE locus, with rs429358 (which tags the APOE ε4 allele) as the lead snv with p = 8x10‐42. 103 independent loci (defined by separation by at least 1 MB) exhibited suggestive significance (p < 1x10‐5), with 7 of these beyond the APOE locus exhibiting replication with at least p < 0.05 and consistent direction betas for the effect allele in Bellenguez, et al. 2022 summary statistics. These loci included rs113181288 on chromosome 1 Between ELF3 and ENSG00000294430, rs4971744 on chromosome 2 (NRXN1‐DT intronic), rs76343365 on chromosome 4 between ENSG00000289869 and ENSG00000250945, rs7442695 on chromosome 5 (ENSG00000294529 intronic), rs62437151 on chromosome 6 (ENSG00000223786 intronic), rs117134121 on chromosome 10 (ADARB2 Intronic), and rs2278745 on chromosome 10 (HK1 Intronic). GWAS for FTD and burden analyses for AD and FTD are underway. Conclusion Expansion of recruitment efforts for genetic studies in ADRD has great potential to nominate new hits for further study. This analysis is an important step forward for representation of Latin Americans in genetic association studies for ADRD.