PATHOLOGY 5 Promising, but in need of further validation Implementation challenges of blood biomarkers for Alzheimer’s disease Blood-based biomarker (BBB) tests may represent the best weapon to combat the soaring rates of Alzheimer’s disease (AD) throughout the world. Existing clinically validated tests are cur- rently deployed to facilitate diag- nosis, to monitor disease and ef- fectiveness of to quantify progression, and to de- termine if a patient is appropri- ate for treatment or participation in a clinical trial. treatments, Historically, diagnosis of AD has been based on clinical observa- tions and apparent symptoms, and, for those with access and the funds to pay, lumbar spinal puncture for a cerebrospinal fluid (CSF) test or for a PET imaging scan. With the proliferation of BBB tests in clinical development, and with increasing levels of accuracy at- tained, they are expected to be- come a global tool to fight this most common of dementias. How- ever, there are many challenges to be overcome yet, both with the tests themselves and with their clinical implementation. Test equipment challenges The most accurate tests today use mass spectroscopy, which outper- form immune-based methods of measuring plasma in accuracy and reliability. Korean researchers from Hanyang University College of Medicine in Seoul conducted an in- depth review of current methodol- ogies used in published research to measure Amyloid-beta (Aβ) plas- ma. They discovered ‘considerable techniques Ionization-mass variance in the diagnostic efficacy of plasma Aβ, contingent upon the em- measurement ployed. spec- troscopy exhibited superior per- formance, while single molecule array (SIMOA) technology did not yield comparable results,’ wrote lead author Hyuk Sung Kwon,1 Mass spectrometry-based assays require specific expertise and in- frastructure, are time consuming, and yield lower throughput with immunoassays. The equipment is expensive and not available in many hospital and clinic labora- tories.2 However, immune-based methods are currently used for CSF analysis. In addition to immunoassays pro- ducing less accurate results of BBB tests they are also subject to batch- to-batch variation, antibody repro- ducibility, and potential cross- reactivity. They offer automated processing, lower cost, and can de- liver rapid turnaround time for point-of-care testing capability. And equipment is in the lab. These fac- tors make a strong case for the de- velopment of BBB tests specifically designed for immunoassays. Standardisation challenges Another challenge relates to col- lecting viable samples for process- ing in remote or low-economy geo- graphic areas with inadequate laboratory infrastructure. Expan- sion of testing capability of more robust samples, such as dried blood spot, could help resolve such issues. When multiple tests are available from multiple vendors, the cost of blood biomarker analysis is ex- pected to drop. While this is ex- pected to make BBB testing more accessible throughout the world, standardisation for blood biom- arker measurements is imperative. Reproducible, accurate, and con- sistent results are essential. The Global Biomarker Standardization Consortium of the Alzheimer’s As- sociation has been overseeing this critical issue as well as the devel- opment of certified reference ma- terial. Both tasks are enormous in scope and scale, but essential for wide- spread global adoption. Prof. Michel Schöll, Ph.D., of the University of Gothenburg and the Wallenberg Centre for Molecular and Translational Medicine, and colleagues, write: ‘Standardisation challenges will vary greatly de- pending on the blood biomarker and analytic approaches used for its measurement.’ They add, ‘True standardisation will require the derival and validation of cutoffs that are translatable between me- thodological approaches for re- spective blood biomarkers.’ Standardisation reference values are made more complex by the fact that the requirements for the diag- nostic performance of a biomarker are determined by the BBB test’s context of use. As an example, a test to “rule in” AD needs a higher specificity cut point to minimise false positives, whereas a “rule out” test needs a high sensitivity cut point, to minimize false negatives.3 Challenges of population ethnic di- versity, medical comorbidities, and confounding factors Most BBB tests have been tested and validated in clinical trials with patient cohorts of non-Hispanic Caucasian people, who have few health-related comorbidities, and who live in developed economies in countries north of the Equator. Research is starting to reveal that co-morbidities, such as chronic kidney disease, hypertension, his- tory of cancer and/or cardiac ar- rest, diabetes, and some pre- scription drugs, can each impact biomarker concentrations in the blood. Alzheimer’s BBB research of the di- verse ethnic, genetic, cultural and demographic factors, and socioeco- nomic different populations of Af- rica, South Asia, Central America and South America has just begun, and is sparse compared to research in Europe, North America, China, Korea ap- proximately 60% of people living with dementia are estimated to be from low-income and middle- income countries in these under- researched areas.4 Japan. Yet, and This is a massive and complex challenge. ‘The unavailability of re- liable reference intervals for highly diverse populations could lead to the misinterpretation of laboratory test results and contribute to mis- diagnosis and inappropriate clini- cal intervention in a diverse real- setting with world greater heterogeneity among individuals,’ writes Schöll and his multi-national team of co-authors. Harald Hampel, MD, PhD, Chief Medical Officer and Senior Vice President, Neurology from Japan- based pharmaceutical company Eisai, and co-authors are more blunt: ‘While the performance of BBBs in highly selective popu- lations provides initial information, a broader understanding of how these biomarkers behave within the global community at large is needed to provide clinical guid- ance. It is imperative to conduct rigorous validation studies in more representative, real-world popu- determine which lations measures perform most con- sistently and to establish cutoffs and reference intervals that per- form reliably across all patient groups.’ to BBB tests in current clinical use are making diagnoses and AD monitoring more precise, and are facilitating AD research through better selection of patient cohorts for clinical trials. Still, it is going to take years before BBB testing can reach the lofty but much needed goal of stemming the epidemic of AD. ■ Report: Cynthia Keen 1. Kwon HS, Yu H-J, Koh S-H. Revolutionizing Alzheimer‘s Diagnosis and Management: The Dawn of Biomarker-Based Precision Medi- cine. Disord. 2024;23(4):188–201. doi.org/ 10.12779/dnd.2024.23.4.188. Neurocogn Dement 2. Schöll M, Verberk IMW, del Campo M, et al. Biomarkers of Neurodegeneration 2: Chal- lenges in the practical implementation of blood biomarkers for Alzheimer’s disease. Lancet Healthy Longev. 2024:S:100630. doi. org/10.1016/j.lanhl.2024.07.013. 3. Hampel H, Hu Y, Cummings J, et al. Blood- based biomarkers for Alzheimer’s disease: Current state and future use in a transformed global landscape. Neuron. 2023;111(18):2781–2799. doi: 10.1016/j.neur- on.2023.05.017. healthcare 4. McGlinchey E, Duran-Aniotz C, Akinyemi R, et al. Biomarkers of Neurodegeneration 5: Biomarkers of neurodegeneration across the Global South. Lancet Healthy Longev. 2024 Oct;5(10):100616. doi: 10.1016/S2666–7568(24)00132–6. New disovery could prevent memory loss in Alzheimer‘s patients Research A gene once believed to fight only viral infections could also hold the key to preventing mem- ory loss in Alzheimer’s patients. Researchers from National Yang Ming Chiao Tung University (NYCU) and Taiwan’s National Health Institutes (NHRI) have revealed that the immune gene CLEC5A plays a critical role in the progression of Alzheimer’s disease, rewriting the scientific community’s long- held understanding of dementia. Published in the Journal of Neur- oinflammation, results offer new into Alz- heimer’s disease mechanisms and pave the way for new drug development. insights their Traditionally, CLEC5A has been as- sociated with viral defense, activat- ing the immune system in response to diseases like dengue fever, Jap- www.healthcare-in-europe.com U C Y N © The research team (from right): NHRI Di- rector Dr. Shie-Liang Hsieh, NYCU Insti- tute of Brain Science Associate Profes- sor Han-Juo Cheng, and Ph.D. student Yu-Yi Lin. anese encephalitis, influenza, and Covid-19. It has also been linked to the deadly „cytokine storm“ phe- nomenon. However, in a surprising twist, a research team led by As- sociate Professor Han-Juo Cheng of NYCU‘s Institute of Brain Science and Dr. Shie-Liang Hsieh, Director of NHRI‘s Immunology Research Center, discovered that this gene also plays a pivotal role in Alz- heimer‘s disease. that lacked Using genetic engineering tech- niques, the team bred Alzheimer‘s model mice the CLEC5A gene and compared them with normal Alzheimer‘s mice. The results were astonishing: mice without the CLEC5A gene perform- ed significantly better in memory and learning tests. They showed a marked in harmful β-amyloid plaque accumulation—a hallmark of Alzheimer‘s pathology. reduction Professor Cheng explained that microglia—the brain’s resident im- mune cells—become hyperactive in response to abnormal β-amyloid buildup, mistakenly attacking healthy neurons and accelerating disease progression. However, when CLEC5A was removed, not only did microglial inflammation decrease, but their ability to clear β-amyloid improved dramatically, slowing the progression of brain degeneration. This discovery positions CLEC5A as a promising new therapeutic tar- get for Alzheimer’s. By designing drugs to block this gene’s protein function, scientists believe they may open a new front in the battle against dementia. “It started as a hunch without solid evidence,” ad- mitted Dr. Hsieh, who previously identified CLEC5A as a key factor in severe dengue and Japanese en- cephalitis cases. Initially, the team was uncertain whether this virus- related gene could also be im- plicated in Alzheimer’s. However, further that CLEC5A doesn’t just recognize vi- ruses—it’s also involved in auto- immune diseases like lupus, raising research revealed suspicions that it might mistakenly attack the brain’s nerve cells. This study also credits NYCU doc- toral students Yu-Yi Lin and Wen- Han Chang for their critical con- tributions. The findings have drawn significant attention from the international scientific commu- nity. As Alzheimer’s cases rise globally, this breakthrough led by Taiwan’s scientific teams not only offers a fresh perspective on the disease’s origins but also points to an en- tirely new direction for drug devel- opment, the research team hopes. Shortly, targeted therapies against CLEC5A could offer countless families a new beacon of hope in the fight against memory loss. ■ Source: National Yang Ming Chiao Tung University