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Kershner JR. Early life stress, literacy and dyslexia: an evolutionary perspective. Brain Struct Funct 2024; 229:809-822. [PMID: 38436668 PMCID: PMC11003919 DOI: 10.1007/s00429-024-02766-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 01/18/2024] [Indexed: 03/05/2024]
Abstract
Stress and learning co-evolved in parallel, with their interdependence critical to the survival of the species. Even today, the regulation of moderate levels of stress by the central autonomic network (CAN), especially during pre- and post-natal periods, facilitates biological adaptability and is an essential precursor for the cognitive requisites of learning to read. Reading is a remarkable evolutionary achievement of the human brain, mysteriously unusual, because it is not pre-wired with a genetic address to facilitate its acquisition. There is no gene for reading. The review suggests that reading co-opts a brain circuit centered in the left hemisphere ventral occipital cortex that evolved as a domain-general visual processor. Its adoption by reading depends on the CAN's coordination of the learning and emotional requirements of learning to read at the metabolic, cellular, synaptic, and network levels. By stabilizing a child's self-control and modulating the attention network's inhibitory controls over the reading circuit, the CAN plays a key role in school readiness and learning to read. In addition, the review revealed two beneficial CAN evolutionary adjustments to early-life stress "overloads" that come with incidental costs of school under-performance and dyslexia. A short-term adaptation involving methylation of the FKBP5 and NR3C1 genes is a liability for academic achievement in primary school. The adaptation leading to dyslexia induces alterations in BDNF trafficking, promoting long-term adaptive fitness by protecting against excessive glucocorticoid toxicity but risks reading difficulties by disruptive signaling from the CAN to the attention networks and the reading circuit.
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Affiliation(s)
- John R Kershner
- Department of Applied Psychology and Human Resources, University of Toronto, Toronto, ON, M5S 1A1, Canada.
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2
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Theodoridou D, Tsiantis CO, Vlaikou AM, Chondrou V, Zakopoulou V, Christodoulides P, Oikonomou ED, Tzimourta KD, Kostoulas C, Tzallas AT, Tsamis KI, Peschos D, Sgourou A, Filiou MD, Syrrou M. Developmental Dyslexia: Insights from EEG-Based Findings and Molecular Signatures-A Pilot Study. Brain Sci 2024; 14:139. [PMID: 38391714 PMCID: PMC10887023 DOI: 10.3390/brainsci14020139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 01/25/2024] [Accepted: 01/26/2024] [Indexed: 02/24/2024] Open
Abstract
Developmental dyslexia (DD) is a learning disorder. Although risk genes have been identified, environmental factors, and particularly stress arising from constant difficulties, have been associated with the occurrence of DD by affecting brain plasticity and function, especially during critical neurodevelopmental stages. In this work, electroencephalogram (EEG) findings were coupled with the genetic and epigenetic molecular signatures of individuals with DD and matched controls. Specifically, we investigated the genetic and epigenetic correlates of key stress-associated genes (NR3C1, NR3C2, FKBP5, GILZ, SLC6A4) with psychological characteristics (depression, anxiety, and stress) often included in DD diagnostic criteria, as well as with brain EEG findings. We paired the observed brain rhythms with the expression levels of stress-related genes, investigated the epigenetic profile of the stress regulator glucocorticoid receptor (GR) and correlated such indices with demographic findings. This study presents a new interdisciplinary approach and findings that support the idea that stress, attributed to the demands of the school environment, may act as a contributing factor in the occurrence of the DD phenotype.
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Affiliation(s)
- Daniela Theodoridou
- Laboratory of Biology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Christos-Orestis Tsiantis
- Laboratory of Biology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Angeliki-Maria Vlaikou
- Biomedical Research Institute, Foundation for Research and Technology-Hellas (FORTH), 45110 Ioannina, Greece
- Laboratory of Biochemistry, Department of Biological Applications and Technology, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Vasiliki Chondrou
- Laboratory of Biology, School of Science and Technology, Hellenic Open University, 26335 Patras, Greece
| | - Victoria Zakopoulou
- Department of Speech and Language Therapy, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Pavlos Christodoulides
- Department of Speech and Language Therapy, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
- Laboratory of Physiology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Emmanouil D Oikonomou
- Department of Informatics and Telecommunications, School of Informatics & Telecommunications, University of Ioannina, 47100 Arta, Greece
| | - Katerina D Tzimourta
- Department of Electrical and Computer Engineering, University of Western Macedonia, 50100 Kozani, Greece
| | - Charilaos Kostoulas
- Laboratory of Medical Genetics, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Alexandros T Tzallas
- Department of Informatics and Telecommunications, School of Informatics & Telecommunications, University of Ioannina, 47100 Arta, Greece
| | - Konstantinos I Tsamis
- Laboratory of Physiology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Dimitrios Peschos
- Laboratory of Physiology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Argyro Sgourou
- Laboratory of Biology, School of Science and Technology, Hellenic Open University, 26335 Patras, Greece
| | - Michaela D Filiou
- Biomedical Research Institute, Foundation for Research and Technology-Hellas (FORTH), 45110 Ioannina, Greece
- Laboratory of Biochemistry, Department of Biological Applications and Technology, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
| | - Maria Syrrou
- Laboratory of Biology, Faculty of Medicine, School of Health Sciences, University of Ioannina, 45110 Ioannina, Greece
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Zaki ZMM, Ali SA, Ghazali MM, Jam FA. Genetic Modifications of Developmental Dyslexia and Its Representation Using In Vivo, In Vitro Model. Glob Med Genet 2024; 11:76-85. [PMID: 38414980 PMCID: PMC10898997 DOI: 10.1055/s-0044-1781456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/29/2024] Open
Abstract
Dyslexia is a genetic and heritable disorder that has yet to discover the treatment of it, especially at the molecular and drug intervention levels. This review provides an overview of the current findings on the environmental and genetic factors involved in developmental dyslexia. The latest techniques used in diagnosing the disease and macromolecular factors findings may contribute to a higher degree of development in detangling the proper management and treatment for dyslexic individuals. Furthermore, this review tried to put together all the models used in the current dyslexia research for references in future studies that include animal models as well as in vitro models and how the previous research has provided consistent data across many years and regions. Thus, we suggest furthering the studies using an organoid model based on the existing gene polymorphism, pathways, and neuronal function input.
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Affiliation(s)
- Zakiyyah M M Zaki
- Department of Neurosciences, School of Medical Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
| | - Siti A Ali
- Department of Electronic Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Kampar, Perak, Malaysia
- Centre for Healthcare Science and Technology, Universiti Tunku Abdul Rahman, Kampar, Perak, Malaysia
| | - Mazira M Ghazali
- Department of Neurosciences, School of Medical Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
- Faculty of Medicine, Universiti Sultan Zainal Abidin, Terengganu, Malaysia
| | - Faidruz A Jam
- Department of Biochemistry, Faculty of Medicine, Manipal University College Malaysia, Melaka, Malaysia
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Huang A, Zhang J, Wu K, Liu C, Huang Q, Zhang X, Lin X, Huang Y. Exposure to multiple metals and the risk of dyslexia - A case control study in Shantou, China. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2022; 307:119518. [PMID: 35618141 DOI: 10.1016/j.envpol.2022.119518] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 04/14/2022] [Accepted: 05/19/2022] [Indexed: 02/05/2023]
Abstract
Environmental heavy metal exposure has been considered to be the risk factor for neurodevelopmental disorders in children. However, the available data on the associations between multiple metals exposure and the risk of dyslexia in China are limited. The purpose of our study was to examine the associations between urinary metal concentrations and Chinese dyslexia risk. A total of 56 Chinese dyslexics and 60 typically developing children were recruited. The urinary concentration of 13 metals were measured by inductively coupled plasma-mass spectrometer (ICP-MS). Binary logistic regression and the Probit extension of Bayesian kernel machine regression (BKMR-P) were used to explore the associations between multiple metal exposure and the risk of Chinese dyslexia. Our results indicated that Co, Zn and Pb were significantly associated with Chinese dyslexia in the multiple-metal exposure model. After adjusting the covariates, a positive association was observed between Pb and the risk of Chinese dyslexia, with the odds ratio (OR) in the highest quartiles of 6.81 (95%CI: 1.07-43.19; p-trend = 0.024). Co and Zn were negatively associated with the risk of Chinese dyslexia. Compared to the lowest quartile, the ORs of Co and Zn in the highest quartile are 0.13 (95%CI: 0.02-0.72; p-trend = 0.026) and 0.18 (95%CI: 0.04-0.88; p-trend = 0.038), respectively. In addition, BKMR-P analysis indicated that with the cumulative level across Co, Zn and Pb increased, the risk of Chinese dyslexia gradually declined and then rebounded, albeit non-significantly, and Pb was the major contributor in this association. In general, the urinary concentrations of Co, Zn and Pb were significantly associated with Chinese dyslexia. More prospective studies are needed to confirm the health effects of multiple metals exposure in children with Chinese dyslexia.
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Affiliation(s)
- Anyan Huang
- Mental Health Center, Shantou University Medical College, North Taishan Road, Shantou, 515065, Guangdong Province, China
| | - Jingbing Zhang
- Department of Preventive Medicine, Shantou University Medical College, Shantou, 515041, Guangdong Province, China
| | - Kusheng Wu
- Department of Preventive Medicine, Shantou University Medical College, Shantou, 515041, Guangdong Province, China
| | - Caixia Liu
- Department of Preventive Medicine, Shantou University Medical College, Shantou, 515041, Guangdong Province, China
| | - Qingjun Huang
- Mental Health Center, Shantou University Medical College, North Taishan Road, Shantou, 515065, Guangdong Province, China
| | - Xuanzhi Zhang
- Mental Health Center, Shantou University Medical College, North Taishan Road, Shantou, 515065, Guangdong Province, China
| | - Xuecong Lin
- Mental Health Center, Shantou University Medical College, North Taishan Road, Shantou, 515065, Guangdong Province, China
| | - Yanhong Huang
- Mental Health Center, Shantou University Medical College, North Taishan Road, Shantou, 515065, Guangdong Province, China
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Kershner JR. Multisensory deficits in dyslexia may result from a locus coeruleus attentional network dysfunction. Neuropsychologia 2021; 161:108023. [PMID: 34530025 DOI: 10.1016/j.neuropsychologia.2021.108023] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 08/06/2021] [Accepted: 09/11/2021] [Indexed: 12/13/2022]
Abstract
A fundamental educational requirement of beginning reading is to learn, access, and rapidly process associations between novel visuospatial symbols and their phonological representations in speech. Children with difficulties in such cross-modal integration are often divided into dyslexia subtypes, based on whether their primary problem is with the written or spoken component of decoding. The present review suggests that starting in infancy, perceptions of audiovisual speech are integrated by mutual oscillatory phase-resetting between sensory cortices, and throughout development visual and auditory experiences are coupled into unified perceptions. Entirely separate subtypes are incompatible with this view. Visual or auditory deficits will invariably affect processing to some degree in both domains. It is suggested that poor auditory/visual integration may be diagnostic for both forms of dyslexia, stemming from an encoding weakness in the early cross-sensory binding of audiovisual speech. The review presents a model of dyslexia as a dysfunction of the large-scale ventral and dorsal attention networks controlling such binding. Excessive glutamatergic neuronal excitability of the attention networks by the Locus coeruleus-norepinephrine system may interfere with multisensory integration, with deleterious effects on the acquisition of reading by degrading graphene/phoneme conversion.
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Affiliation(s)
- John R Kershner
- Dept. of Applied Psychology and Human Resources University of Toronto, ON, M5S 1A1, Canada.
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Developmental Dyslexia: Environment Matters. Brain Sci 2021; 11:brainsci11060782. [PMID: 34199166 PMCID: PMC8231524 DOI: 10.3390/brainsci11060782] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 06/09/2021] [Accepted: 06/11/2021] [Indexed: 12/15/2022] Open
Abstract
Developmental dyslexia (DD) is a multifactorial, specific learning disorder. Susceptibility genes have been identified, but there is growing evidence that environmental factors, and especially stress, may act as triggering factors that determine an individual's risk of developing DD. In DD, as in most complex phenotypes, the presence of a genetic mutation fails to explain the broad phenotypic spectrum observed. Early life stress has been repeatedly associated with the risk of multifactorial disorders, due to its effects on chromatin regulation, gene expression, HPA axis function and its long-term effects on the systemic stress response. Based on recent evidence, we discuss the potential role of stress on DD occurrence, its putative epigenetic effects on the HPA axis of affected individuals, as well as the necessity of early and appropriate intervention, based on the individual stress-associated (endo)phenotype.
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Autophagy status as a gateway for stress-induced catecholamine interplay in neurodegeneration. Neurosci Biobehav Rev 2021; 123:238-256. [PMID: 33497785 DOI: 10.1016/j.neubiorev.2021.01.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 01/08/2021] [Accepted: 01/09/2021] [Indexed: 12/13/2022]
Abstract
The catecholamine-containing brainstem nuclei locus coeruleus (LC) and ventral tegmental area (VTA) are critically involved in stress responses. Alterations of catecholamine systems during chronic stress may contribute to neurodegeneration, including cognitive decline. Stress-related catecholamine alterations, while contributing to anxiety and depression, might accelerate neuronal degeneration by increasing the formation of toxic dopamine and norepinephrine by-products. These, in turn, may impair proteostasis within a variety of cortical and subcortical areas. In particular, the molecular events governing neurotransmission, neuroplasticity, and proteostasis within LC and VTA affect a variety of brain areas. Therefore, we focus on alterations of autophagy machinery in these nuclei as a relevant trigger in this chain of events. In fact, these catecholamine-containing areas are mostly prone to autophagy-dependent neurodegeneration. Thus, we propose a dynamic hypothesis according to which stress-induced autophagy alterations within the LC-VTA network foster a cascade towards early neurodegeneration within these nuclei.
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Kershner JR. An Evolutionary Perspective of Dyslexia, Stress, and Brain Network Homeostasis. Front Hum Neurosci 2021; 14:575546. [PMID: 33551772 PMCID: PMC7859477 DOI: 10.3389/fnhum.2020.575546] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 12/18/2020] [Indexed: 12/20/2022] Open
Abstract
Evolution fuels interindividual variability in neuroplasticity, reflected in brain anatomy and functional connectivity of the expanding neocortical regions subserving reading ability. Such variability is orchestrated by an evolutionarily conserved, competitive balance between epigenetic, stress-induced, and cognitive-growth gene expression programs. An evolutionary developmental model of dyslexia, suggests that prenatal and childhood subclinical stress becomes a risk factor for dyslexia when physiological adaptations to stress promoting adaptive fitness, may attenuate neuroplasticity in the brain regions recruited for reading. Stress has the potential to blunt the cognitive-growth functions of the predominantly right hemisphere Ventral and Dorsal attention networks, which are primed with high entropic levels of synaptic plasticity, and are critical for acquiring beginning reading skills. The attentional networks, in collaboration with the stress-responsive Default Mode network, modulate the entrainment and processing of the low frequency auditory oscillations (1-8 Hz) and visuospatial orienting linked etiologically to dyslexia. Thus, dyslexia may result from positive, but costly adaptations to stress system dysregulation: protective measures that reset the stress/growth balance of processing to favor the Default Mode network, compromising development of the attentional networks. Such a normal-variability conceptualization of dyslexia is at odds with the frequent assumption that dyslexia results from a neurological abnormality. To put the normal-variability model in the broader perspective of the state of the field, a traditional evolutionary account of dyslexia is presented to stimulate discussion of the scientific merits of the two approaches.
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Affiliation(s)
- John R. Kershner
- Department of Applied Psychology, University of Toronto, Toronto, ON, Canada
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