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Man S, Chen B, Zhang Y, Xu H, Liu Y, Gao Y, Chen Y, Chen Q, Zhang M. The Associations Between Cataracts and Alzheimer's Disease: A Bidirectional Two-Sample Mendelian Randomization Study. J Alzheimers Dis 2023; 92:1451-1458. [PMID: 36911941 DOI: 10.3233/jad-221137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
BACKGROUND The relationship between cataracts and Alzheimer's disease (AD) has been reported in recent observational studies. However, it is still unclear whether a causal effect of cataracts on AD or reverse causation exists. OBJECTIVE To explore the association between cataracts and AD genetically, we performed a bidirectional two-sample Mendelian randomization study. METHODS We obtained genetic instrumental variables related to cataracts and AD from recently published genome-wide association studies (GWASs). SNP-outcome associations for AD were obtained from a GWAS with 111,326 cases and 677,663 controls. SNP-outcome associations for cataracts were drawn from two sources: a GWAS with 67,844 cases and 517,399 controls and the FinnGen consortium (42,843 cases and 262,698 controls). Inverse variance weighted (IVW) was used as the primary method for Mendelian randomization (MR) analyses. RESULTS No genetic evidence suggested that cataracts were associated with the risk of AD (IVW odds ratio =1.04, 95% confidence interval: 0.98-1.10, p=0.199). In contrast, an effect of genetically determined AD on a decreased risk of cataract was observed with suggestive evidence (IVW odds ratio =0.96, 95% confidence interval: 0.93-0.99, p=0.004). However, this result might be distorted by survival bias. CONCLUSION Genetically determined cataracts were not related to AD, as demonstrated by our study. In contrast, there was suggestive evidence that AD might prevent cataract development, but there might be potential survival bias. To define the exact association between the two diseases, more prospective research and studies on the pathogenesis are needed.
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Affiliation(s)
- Shulei Man
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Boran Chen
- Department of Neurosurgery, West China Hospital, Sichuan University, Chengdu, China
| | - Yifan Zhang
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Hanyue Xu
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Yu Liu
- Department of Neurosurgery, West China Hospital, Sichuan University, Chengdu, China
| | - Yuzhu Gao
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Yi Chen
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Qing Chen
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Ming Zhang
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
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Hussain A, Sheikh Z, Subramanian M. The Eye as a Diagnostic Tool for Alzheimer’s Disease. Life (Basel) 2023; 13:life13030726. [PMID: 36983883 PMCID: PMC10052959 DOI: 10.3390/life13030726] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2023] [Revised: 02/23/2023] [Accepted: 03/04/2023] [Indexed: 03/10/2023] Open
Abstract
Alzheimer’s disease (AD) is a progressive neurodegenerative disorder impacting cognition, function, and behavior in the elderly population. While there are currently no disease-modifying agents capable of curing AD, early diagnosis and management in the preclinical stage can significantly improve patient morbidity and life expectancy. Currently, the diagnosis of Alzheimer’s disease is a clinical one, often supplemented by invasive and expensive biomarker testing. Over the last decade, significant advancements have been made in our understanding of AD and the role of ocular tissue as a potential biomarker. Ocular biomarkers hold the potential to provide noninvasive and easily accessible diagnostic and monitoring capabilities. This review summarizes current research for detecting biomarkers of Alzheimer’s disease in ocular tissue.
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Li TR, Yang Q, Hu X, Han Y. Biomarkers and Tools for Predicting Alzheimer's Disease in the Preclinical Stage. Curr Neuropharmacol 2022; 20:713-737. [PMID: 34030620 PMCID: PMC9878962 DOI: 10.2174/1570159x19666210524153901] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 04/27/2021] [Accepted: 05/08/2021] [Indexed: 11/22/2022] Open
Abstract
Alzheimer's disease (AD) is the only leading cause of death for which no disease-modifying therapy is currently available. Over the past decade, a string of disappointing clinical trial results has forced us to shift our focus to the preclinical stage of AD, which represents the most promising therapeutic window. However, the accurate diagnosis of preclinical AD requires the presence of brain β- amyloid deposition determined by cerebrospinal fluid or amyloid-positron emission tomography, significantly limiting routine screening and diagnosis in non-tertiary hospital settings. Thus, an easily accessible marker or tool with high sensitivity and specificity is highly needed. Recently, it has been discovered that individuals in the late stage of preclinical AD may not be truly "asymptomatic" in that they may have already developed subtle or subjective cognitive decline. In addition, advances in bloodderived biomarker studies have also allowed the detection of pathologic changes in preclinical AD. Exosomes, as cell-to-cell communication messengers, can reflect the functional changes of their source cell. Methodological advances have made it possible to extract brain-derived exosomes from peripheral blood, making exosomes an emerging biomarker carrier and liquid biopsy tool for preclinical AD. The eye and its associated structures have rich sensory-motor innervation. In this regard, studies have indicated that they may also provide reliable markers. Here, our report covers the current state of knowledge of neuropsychological and eye tests as screening tools for preclinical AD and assesses the value of blood and brain-derived exosomes as carriers of biomarkers in conjunction with the current diagnostic paradigm.
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Affiliation(s)
- Tao-Ran Li
- Department of Neurology, Xuanwu Hospital of Capital Medical University, Beijing, 100053, China
| | - Qin Yang
- Department of Neurology, Xuanwu Hospital of Capital Medical University, Beijing, 100053, China
| | - Xiaochen Hu
- Department of Psychiatry, University of Cologne, Medical Faculty, Cologne, 50924, Germany
| | - Ying Han
- Department of Neurology, Xuanwu Hospital of Capital Medical University, Beijing, 100053, China;,Center of Alzheimer’s Disease, Beijing Institute for Brain Disorders, Beijing, 100053, China;,National Clinical Research Center for Geriatric Disorders, Beijing, 100053, China;,School of Biomedical Engineering, Hainan University, Haikou, 570228, China;,Address correspondence to this author at the Department of Neurology, Xuanwu Hospital of Capital Medical University, Beijing, 100053, China; Tel: +86 13621011941; E-mail:
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Alzheimer's Disease Seen through the Eye: Ocular Alterations and Neurodegeneration. Int J Mol Sci 2022; 23:ijms23052486. [PMID: 35269629 PMCID: PMC8910735 DOI: 10.3390/ijms23052486] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 02/21/2022] [Accepted: 02/22/2022] [Indexed: 12/18/2022] Open
Abstract
Alzheimer’s Disease (AD) is one of the main neurodegenerative diseases worldwide. Unfortunately, AD shares many similarities with other dementias at early stages, which impedes an accurate premortem diagnosis. Therefore, it is urgent to find biomarkers to allow for early diagnosis of the disease. There is increasing scientific evidence highlighting the similarities between the eye and other structures of the CNS, suggesting that knowledge acquired in eye research could be useful for research and diagnosis of AD. For example, the retina and optic nerve are considered part of the central nervous system, and their damage can result in retrograde and anterograde axon degeneration, as well as abnormal protein aggregation. In the anterior eye segment, the aqueous humor and tear film may be comparable to the cerebrospinal fluid. Both fluids are enriched with molecules that can be potential neurodegenerative biomarkers. Indeed, the pathophysiology of AD, characterized by cerebral deposits of amyloid-beta (Aβ) and tau protein, is also present in the eyes of AD patients, besides numerous structural and functional changes observed in the structure of the eyes. Therefore, all this evidence suggests that ocular changes have the potential to be used as either predictive values for AD assessment or as diagnostic tools.
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5
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Affiliation(s)
- Roy Quinlan
- Biomedical Sciences, Department of Biosciences, The University of Durham, Upper Mountjoy Science Site, Durham, DH1 3LE, UK.
| | - Frank Giblin
- Biomedical Sciences Emeritus, Eye Research Institute, Oakland University, Rochester, MI, 48309, USA.
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Chalkias IN, Tegos T, Topouzis F, Tsolaki M. Ocular biomarkers and their role in the early diagnosis of neurocognitive disorders. Eur J Ophthalmol 2021; 31:2808-2817. [PMID: 34000876 DOI: 10.1177/11206721211016311] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Given the fact that different types of dementia can be diagnosed only postmortem or when the disease has progressed enough to cause irreversible damage to certain brain areas, there has been an increasing need for the development of sensitive and reliable methods that can detect early preclinical forms of dementia, before the symptoms have even appeared. Ideally, such a method would have the following characteristics: to be inexpensive, sensitive and specific, Non-invasive, fast and easily accessible. The ophthalmologic examination and especially the study of the retina, has caught the attention of many researchers, as it can provide a lot of information about the CNS and it fulfills many of the aforementioned criteria. Since the introduction of the non-invasive optical coherence tomography (OCT) and the newly developed modality OCT-angiography (OCT-A) that can demonstrate the structure and the microvasculature of the retina and choroid, respectively, there have been promising results regarding the value of the ophthalmologic examination in the early diagnosis of Alzheimer's disease. In this review paper, we summarize and discuss the ocular findings in patients with cognitive impairment disorders and we highlight the importance of the ophthalmologic examination to the diagnosis of these disorders.
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Affiliation(s)
- Ioannis-Nikolaos Chalkias
- 1st Department of Ophthalmology, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Makedonia Thraki, Greece
| | - Thomas Tegos
- 1st Department of Neurology, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Makedonia Thraki, Greece
| | - Fotis Topouzis
- 1st Department of Ophthalmology, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Makedonia Thraki, Greece
| | - Magda Tsolaki
- 1st Department of Neurology, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Makedonia Thraki, Greece.,Greek Association of Alzheimer's Disease and Related Disorders, Thessaloniki, Greece
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In-vivo anterior segment OCT imaging provides unique insight into cerulean blue-dot opacities and cataracts in Down syndrome. Sci Rep 2020; 10:10031. [PMID: 32572106 PMCID: PMC7308272 DOI: 10.1038/s41598-020-66642-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 05/21/2020] [Indexed: 12/31/2022] Open
Abstract
Down syndrome (DS) is frequently associated with cataract, but there remains scant information about DS cataract morphology. Supra-nuclear cataracts in DS have been proposed as indicative of beta-amyloid (Aβ) aggregation and thus potential biomarkers for Alzheimer’s (AD). This study employed anterior segment OCT (AS-OCT) and slit-lamp (SL) photography to image the crystalline lens in DS, compared with adult controls. Lens images were obtained post-dilation. Using MATLAB, AS-OCT images were analysed and lens opacities calculated as pixel intensity and area ratios. SL images were classified using LOCS III. Subjects were n = 28 DS (mean ± SD 24.1 ± 14.3years), and n = 36 controls (54.0 ± 3.4years). For the DS group, AS-OCT imaging revealed the frequent presence of small dot opacities (27 eyes, 50%) in the cortex and nucleus of the lens, covering an area ranging from 0.2–14%. There was no relation with age or visual acuity and these dot opacities (p > 0.5) and they were not present in any control lenses. However, their location and morphology does not coincide with previous reports linking these opacities with Aβ accumulation and AD. Four participants (14%) in the DS group had clinically significant age-related cataracts, but there was no evidence of early onset of age-related cataracts in DS.
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Abstract
PURPOSE OF REVIEW The incidence of Alzheimer's disease is increasing. Premortem diagnosis of Alzheimer's disease is now possible but require invasive and expensive testing such as PET amyloid beta binding and/or spinal fluid amyloid beta levels. There is a great need for minimally invasive and inexpensive biomarkers to allow for early diagnosis and intervention. RECENT FINDINGS There has been a large volume of literature assessing ocular biomarkers for Alzheimer's disease. Much of the research to date has significant limitations, including sample size, variable diagnostic criteria for Alzheimer's disease, lack of biomarker assessment, and focus on patients with well established dementia. Work that is more recent has included individuals with early and preclinical Alzheimer's disease with biomarkers included in the design. These studies have shown consistent features of visual pathway involvement in Alzheimer's disease, even in the earliest and preclinical stages. SUMMARY It is possible that in the future, ocular biomarkers (particularly retinal imaging techniques) may be part of a multimodality alogorithm screening for preclinical Alzheimer's disease, perhaps combined with other methods, such as blood-based biomarkers.
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Cerquera-Jaramillo MA, Nava-Mesa MO, González-Reyes RE, Tellez-Conti C, de-la-Torre A. Visual Features in Alzheimer's Disease: From Basic Mechanisms to Clinical Overview. Neural Plast 2018; 2018:2941783. [PMID: 30405709 PMCID: PMC6204169 DOI: 10.1155/2018/2941783] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 08/07/2018] [Indexed: 12/16/2022] Open
Abstract
Alzheimer's disease (AD) is the leading cause of dementia worldwide. It compromises patients' daily activities owing to progressive cognitive deterioration, which has elevated direct and indirect costs. Although AD has several risk factors, aging is considered the most important. Unfortunately, clinical diagnosis is usually performed at an advanced disease stage when dementia is established, making implementation of successful therapeutic interventions difficult. Current biomarkers tend to be expensive, insufficient, or invasive, raising the need for novel, improved tools aimed at early disease detection. AD is characterized by brain atrophy due to neuronal and synaptic loss, extracellular amyloid plaques composed of amyloid-beta peptide (Aβ), and neurofibrillary tangles of hyperphosphorylated tau protein. The visual system and central nervous system share many functional components. Thus, it is plausible that damage induced by Aβ, tau, and neuroinflammation may be observed in visual components such as the retina, even at an early disease stage. This underscores the importance of implementing ophthalmological examinations, less invasive and expensive than other biomarkers, as useful measures to assess disease progression and severity in individuals with or at risk of AD. Here, we review functional and morphological changes of the retina and visual pathway in AD from pathophysiological and clinical perspectives.
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Affiliation(s)
| | - Mauricio O. Nava-Mesa
- Grupo de Investigación en Neurociencias (NeURos), Escuela de Medicina y Ciencias de la Salud, Universidad del Rosario, Bogotá, Colombia
| | - Rodrigo E. González-Reyes
- Grupo de Investigación en Neurociencias (NeURos), Escuela de Medicina y Ciencias de la Salud, Universidad del Rosario, Bogotá, Colombia
| | - Carlos Tellez-Conti
- Escuela Superior de Oftalmología-Instituto Barraquer de América, Bogotá, Colombia
| | - Alejandra de-la-Torre
- Grupo de Investigación en Neurociencias (NeURos), Escuela de Medicina y Ciencias de la Salud, Universidad del Rosario, Bogotá, Colombia
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10
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Ocular amyloid imaging at the crossroad of Alzheimer's disease and age-related macular degeneration: implications for diagnosis and therapy. J Neurol 2018; 266:1566-1577. [PMID: 30155741 DOI: 10.1007/s00415-018-9028-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 08/18/2018] [Accepted: 08/20/2018] [Indexed: 12/17/2022]
Abstract
Alzheimer's disease (AD) and age-related macular degeneration (AMD) are important disorders of aging, but significant challenges remain in diagnosis and therapy. Amyloid-beta (Aβ), found in the brain and a defining feature of AD, has also been observed in the retina in both AD and AMD. While current diagnostic modalities for detecting Aβ in the brain are costly or invasive, Aβ in the retina can be noninvasively and conveniently imaged using modern photonic imaging systems such as optical coherence tomography (OCT). Moreover, since many of these retinal changes occur before degenerative changes can be detected in the brain, ocular amyloid biomarkers could be utilized to detect AD as well as AMD in their earliest stages when therapy may be most effective in halting disease progression. Novel technologies to quantify retinal biomarkers have the potential to facilitate early diagnosis and noninvasive monitoring of disease progression with important therapeutic implications.
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11
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Peripheral Biomarkers for Early Detection of Alzheimer's and Parkinson's Diseases. Mol Neurobiol 2018; 56:2256-2277. [PMID: 30008073 DOI: 10.1007/s12035-018-1151-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 05/24/2018] [Indexed: 01/18/2023]
Abstract
Neurological disorders are found to be influencing the peripheral tissues outside CNS. Recent developments in biomarkers for CNS have emerged with various diagnostic and therapeutic shortcomings. The role of central biomarkers including CSF-based and molecular imaging-based probes are still unclear for early diagnosis of major neurological diseases. Current trends show that early detection of neurodegenerative diseases with non-invasive methods is a major focus of researchers, and the development of biomarkers aiming peripheral tissues is in demand. Alzheimer's and Parkinson's diseases are known for the progressive loss in neural structures or functions, including the neural death. Various dysfunctions of metabolic and biochemical pathways are associated with early occurrence of neuro-disorders in peripheral tissues including skin, blood cells, and eyes. This article reviews the peripheral biomarkers explored for early detection of Alzheimer's and Parkinson's diseases including blood cells, skin fibroblast, proteomics, saliva, olfactory, stomach and colon, heart and peripheral nervous system, and others. Graphical Abstract.
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12
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Kusne Y, Wolf AB, Townley K, Conway M, Peyman GA. Visual system manifestations of Alzheimer's disease. Acta Ophthalmol 2017; 95:e668-e676. [PMID: 27864881 DOI: 10.1111/aos.13319] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 10/07/2016] [Indexed: 12/13/2022]
Abstract
Alzheimer's disease (AD) is an increasingly common disease with massive personal and economic costs. While it has long been known that AD impacts the visual system, there has recently been an increased focus on understanding both pathophysiological mechanisms that may be shared between the eye and brain and how related biomarkers could be useful for AD diagnosis. Here, were review pertinent cellular and molecular mechanisms of AD pathophysiology, the presence of AD pathology in the visual system, associated functional changes, and potential development of diagnostic tools based on the visual system. Additionally, we discuss links between AD and visual disorders, including possible pathophysiological mechanisms and their relevance for improving our understanding of AD.
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Affiliation(s)
- Yael Kusne
- University of Arizona College of Medicine; Phoenix Arizona USA
| | - Andrew B. Wolf
- University of Colorado School of Medicine; Aurora Colorado USA
| | - Kate Townley
- University of Arizona College of Medicine; Phoenix Arizona USA
| | - Mandi Conway
- University of Arizona College of Medicine; Phoenix Arizona USA
- Arizona Retinal Specialists; Sun City Arizona USA
| | - Gholam A. Peyman
- University of Arizona College of Medicine; Phoenix Arizona USA
- Arizona Retinal Specialists; Sun City Arizona USA
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13
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Hart NJ, Koronyo Y, Black KL, Koronyo-Hamaoui M. Ocular indicators of Alzheimer's: exploring disease in the retina. Acta Neuropathol 2016; 132:767-787. [PMID: 27645291 PMCID: PMC5106496 DOI: 10.1007/s00401-016-1613-6] [Citation(s) in RCA: 173] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 08/29/2016] [Accepted: 09/01/2016] [Indexed: 12/11/2022]
Abstract
Although historically perceived as a disorder confined to the brain, our understanding of Alzheimer's disease (AD) has expanded to include extra-cerebral manifestation, with mounting evidence of abnormalities in the eye. Among ocular tissues, the retina, a developmental outgrowth of the brain, is marked by an array of pathologies in patients suffering from AD, including nerve fiber layer thinning, degeneration of retinal ganglion cells, and changes to vascular parameters. While the hallmark pathological signs of AD, amyloid β-protein (Aβ) plaques and neurofibrillary tangles (NFT) comprising hyperphosphorylated tau (pTau) protein, have long been described in the brain, identification of these characteristic biomarkers in the retina has only recently been reported. In particular, Aβ deposits were discovered in post-mortem retinas of advanced and early stage cases of AD, in stark contrast to non-AD controls. Subsequent studies have reported elevated Aβ42/40 peptides, morphologically diverse Aβ plaques, and pTau in the retina. In line with the above findings, animal model studies have reported retinal Aβ deposits and tauopathy, often correlated with local inflammation, retinal ganglion cell degeneration, and functional deficits. This review highlights the converging evidence that AD manifests in the eye, especially in the retina, which can be imaged directly and non-invasively. Visual dysfunction in AD patients, traditionally attributed to well-documented cerebral pathology, can now be reexamined as a direct outcome of retinal abnormalities. As we continue to study the disease in the brain, the emerging field of ocular AD warrants further investigation of how the retina may faithfully reflect the neurological disease. Indeed, detection of retinal AD pathology, particularly the early presenting amyloid biomarkers, using advanced high-resolution imaging techniques may allow large-scale screening and monitoring of at-risk populations.
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Affiliation(s)
- Nadav J Hart
- Department of Neurosurgery, Maxine Dunitz Neurosurgical Research Institute, Cedars-Sinai Medical Center, 127 S. San Vicente Blvd., Los Angeles, 90048, CA, USA
| | - Yosef Koronyo
- Department of Neurosurgery, Maxine Dunitz Neurosurgical Research Institute, Cedars-Sinai Medical Center, 127 S. San Vicente Blvd., Los Angeles, 90048, CA, USA
| | - Keith L Black
- Department of Neurosurgery, Maxine Dunitz Neurosurgical Research Institute, Cedars-Sinai Medical Center, 127 S. San Vicente Blvd., Los Angeles, 90048, CA, USA
| | - Maya Koronyo-Hamaoui
- Department of Neurosurgery, Maxine Dunitz Neurosurgical Research Institute, Cedars-Sinai Medical Center, 127 S. San Vicente Blvd., Los Angeles, 90048, CA, USA.
- Department of Biomedical Sciences, Cedars-Sinai Medical Center, 110 George Burns Rd., Los Angeles, CA, 90048, USA.
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Lim JKH, Li QX, He Z, Vingrys AJ, Wong VHY, Currier N, Mullen J, Bui BV, Nguyen CTO. The Eye As a Biomarker for Alzheimer's Disease. Front Neurosci 2016; 10:536. [PMID: 27909396 PMCID: PMC5112261 DOI: 10.3389/fnins.2016.00536] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 11/03/2016] [Indexed: 01/08/2023] Open
Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disorder resulting in dementia and eventual death. It is the leading cause of dementia and the number of cases are projected to rise in the next few decades. Pathological hallmarks of AD include the presence of hyperphosphorylated tau and amyloid protein deposition. Currently, these pathological biomarkers are detected either through cerebrospinal fluid analysis, brain imaging or post-mortem. Though effective, these methods are not widely available due to issues such as the difficulty in acquiring samples, lack of infrastructure or high cost. Given that the eye possesses clear optics and shares many neural and vascular similarities to the brain, it offers a direct window to cerebral pathology. These unique characteristics lend itself to being a relatively inexpensive biomarker for AD which carries the potential for wide implementation. The development of ocular biomarkers can have far implications in the discovery of treatments which can improve the quality of lives of patients. In this review, we consider the current evidence for ocular biomarkers in AD and explore potential future avenues of research in this area.
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Affiliation(s)
- Jeremiah K H Lim
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
| | - Qiao-Xin Li
- Melbourne Brain Centre, The Florey Institute of Neuroscience and Mental Health Parkville, VIC, Australia
| | - Zheng He
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
| | - Algis J Vingrys
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
| | - Vickie H Y Wong
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
| | | | | | - Bang V Bui
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
| | - Christine T O Nguyen
- Department of Optometry and Vision Sciences, University of Melbourne Melbourne, VIC, Australia
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Javaid FZ, Brenton J, Guo L, Cordeiro MF. Visual and Ocular Manifestations of Alzheimer's Disease and Their Use as Biomarkers for Diagnosis and Progression. Front Neurol 2016; 7:55. [PMID: 27148157 PMCID: PMC4836138 DOI: 10.3389/fneur.2016.00055] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/29/2016] [Indexed: 12/21/2022] Open
Abstract
Alzheimer's disease (AD) is the most common form of dementia affecting the growing aging population today, with prevalence expected to rise over the next 35 years. Clinically, patients exhibit a progressive decline in cognition, memory, and social functioning due to deposition of amyloid β (Aβ) protein and intracellular hyperphosphorylated tau protein. These pathological hallmarks of AD are measured either through neuroimaging, cerebrospinal fluid analysis, or diagnosed post-mortem. Importantly, neuropathological progression occurs in the eye as well as the brain, and multiple visual changes have been noted in both human and animal models of AD. The eye offers itself as a transparent medium to cerebral pathology and has thus potentiated the development of ocular biomarkers for AD. The use of non-invasive screening, such as retinal imaging and visual testing, may enable earlier diagnosis in the clinical setting, minimizing invasive and expensive investigations. It also potentially improves disease management and quality of life for AD patients, as an earlier diagnosis allows initiation of medication and treatment. In this review, we explore the evidence surrounding ocular changes in AD and consider the biomarkers currently in development for early diagnosis.
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Affiliation(s)
- Fatimah Zara Javaid
- Glaucoma and Retinal Degeneration Research Group, Visual Neurosciences, UCL Institute of Ophthalmology, London, UK
| | - Jonathan Brenton
- Glaucoma and Retinal Degeneration Research Group, Visual Neurosciences, UCL Institute of Ophthalmology, London, UK
| | - Li Guo
- Glaucoma and Retinal Degeneration Research Group, Visual Neurosciences, UCL Institute of Ophthalmology, London, UK
| | - Maria F. Cordeiro
- Glaucoma and Retinal Degeneration Research Group, Visual Neurosciences, UCL Institute of Ophthalmology, London, UK
- Western Eye Hospital, Imperial College Healthcare NHS Trust, London, UK
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Abstract
Age-related cataracts are frequently associated with degenerative changes in the ocular lens including the aggregation of proteins - mainly crystallins, but also other proteins including amyloids (Aβ) leading to the hypothesis that cataracts could be used as "biomarkers" for Alzheimer disease. Even if this hypothesis was rejected by David Beebe's last paper (Bei et al., Exp. Eye Res., 2015), it is a fascinating aspect to look for commonalities between eye diseases and neurological disorders. In this review, I discuss such commonalities between eye and brain mainly from a developmental point of view. The finding of the functional homology of the Drosophila eyeless gene with the mammalian Pax6 gene marks a first highlight in the developmental genetics of the eye - this result destroyed the "dogma" of the different evolutionary routes of eye development in flies and mammals. The second highlight was the finding that Pax6 is also involved in the development of the forebrain supporting the pleiotropic role of many genes. These findings opened a new avenue for research showing that a broad variety of transcription factors, but also structural proteins are involved both, in eye and brain development as well as into the maintenance of the functional integrity of the corresponding tissue(s). In this review recent findings are summarized demonstrating that genes whose mutations have been identified first to be causative for congenital or juvenile eye disorders are also involved in regenerative processes and neurogenesis (Pax6), but also in neurodegenerative diseases like Parkinson (e.g. Pitx3) or in neurological disorders like Schizophrenia (e.g. Crybb1, Crybb2).
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Affiliation(s)
- Jochen Graw
- Helmholtz Zentrum München, Institute of Developmental Genetics, Ingolstaedter Landstr, 1, D-85764 Neuherberg, Germany.
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