Introduction
Developmental dyslexia is one of the most common neurodevelopmental disorders, characterized by persistent difficulties in accurate and fluent word reading and phonological decoding despite normal intelligence and adequate educational opportunities [1,2]. It is classified as a specific subtype of reading disorder. Although dyslexia is primarily defined by deficits in word-level reading, affected children may also exhibit secondary impairments in fluency and reading comprehension that stem from these underlying decoding difficulties. It is estimated that more than 80% of children diagnosed with learning disabilities meet the criteria for dyslexia. Prevalence estimates range from 5% to 20%, depending on the diagnostic standards applied. Dyslexia has traditionally been described as an ‘unexpected difficulty in reading,’ emphasizing the discrepancy between otherwise intact cognitive and linguistic abilities and disproportionately impaired reading skills [2].
The core deficit lies in phonological awareness—namely, the ability to recognize, manipulate, and decode the relationship between graphemes and their corresponding phonemes. This weakness interferes with accurate and fluent word recognition and constitutes the central explanatory framework for both research and clinical diagnosis of dyslexia. Historically, the concept of dyslexia has evolved over more than a century. In 1884, German ophthalmologist Rudolf Berlin first coined the term ‘dyslexia’ to describe patients who, despite normal vision and intelligence, could not learn to read [3]. Early clinical descriptions by James Hinshelwood (1895), who reported cases of ‘word blindness,’ and Pringle Morgan (1896), who published the first detailed case of congenital word blindness in the British Medical Journal, both described children with selective and persistent reading difficulties despite otherwise normal cognitive and linguistic development [3].
These early observations anticipated the modern understanding that dyslexia reflects a specific developmental failure of brain networks responsible for linking visual symbols to spoken language. With the advent of neuroimaging and genetics, growing evidence has confirmed that dyslexia is associated with atypical development of left-hemisphere reading pathways [2,4]. In contemporary diagnostic frameworks, dyslexia is classified under the broader category of specific learning disorders. The Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) (American Psychiatric Association, 2013) defines dyslexia as a ‘specific learning disorder with impairment in reading,’ encompassing not only deficits in accuracy but also impairments in fluency, reading rate, and spelling [5]. Similarly, the International Classification of Diseases, 11th revision (ICD-11) (World Health Organization, 2019) recognizes dyslexia as a subtype of ‘developmental learning disorder,’ stipulating that the diagnosis applies only when reading difficulties cannot be explained by intellectual disability, sensory impairments, or inadequate educational opportunities [6].
Early diagnostic practice relied heavily on clinical observation and the discrepancy between reading achievement and general cognitive ability. However, as converging evidence from genetics, cognitive neuroscience, and neuroimaging accumulated, dyslexia has increasingly been conceptualized as a neurodevelopmental disorder with identifiable biological underpinnings. This paradigm shift reflects a broader scientific movement from phenomenological description toward a neurocognitive and neurobiological construct, emphasizing that dyslexia arises from specific deficits in brain-based processes underlying word reading and phonological decoding rather than from extrinsic factors such as poor instruction or lack of motivation.
Neurobiological Foundations
1. Structural and functional brain alterations
Reading engages a distributed left-hemisphere network encompassing occipito-temporal, temporo-parietal, and frontal regions that coordinate visual, phonological, and semantic processing (Fig. 1) [7]. Recent neuroimaging studies consistently highlight that this left-lateralized reading network operates less efficiently in individuals with dyslexia. Functional magnetic resonance imaging (fMRI) studies in both children and adults with dyslexia typically reveal reduced activation of posterior reading systems, including the left occipito-temporal cortex (visual word form area [VWFA]), the left temporo-parietal cortex (supramarginal and angular gyri), and, to varying degrees, the left inferior frontal gyrus (IFG; Broca’s area).
The VWFA is specialized for orthographic tuning and rapid word recognition; dysfunction in this region has been associated with slow, effortful, ‘letter-by-letter’ reading. The supramarginal gyrus supports grapheme-phoneme conversion and phonological assembly, while the angular gyrus contributes to verbal working memory and semantic integration. The IFG further supports sublexical phonological processing (BA44) and lexico-semantic retrieval (BA45). In dyslexia, these regions are less efficiently recruited, and atypical or compensatory activation of right-hemisphere regions is frequently observed [8].
2. White-matter microstructure
Diffusion tensor imaging studies consistently report reduced integrity in key language tracts, most notably the left arcuate fasciculus (AF), which connects temporo-parietal and frontal language areas, and the corona radiata (CR). Additional alterations have been observed in the superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, and portions of the corpus callosum. A decade-spanning systematic review demonstrated that: (1) reductions in left AF integrity are the most consistently replicated finding across age groups; (2) SLF alterations are primarily detected in school-aged readers and adults; and (3) effects are largely left-lateralized, with some right-hemisphere increases interpreted as compensatory [4]. Longitudinal and family-risk studies further reveal that pre-reading children with familial risk already show lower AF integrity and atypical right-hemisphere activation patterns, which predict later reading outcomes.
3. Genetic contributions
Several candidate susceptibility genes, including doublecortin domain containing 2 (DCDC2), KIAA0319, and roundabout guidance receptor 1 (ROBO1), have been implicated in dyslexia [9]. Although no single gene is determinative, these loci are believed to influence neuronal migration, axon guidance, and myelination, thereby affecting the efficiency of long-range reading networks and their associated white-matter organization [2].
4. The role of the procedural learning system
Beyond deficits in phonological decoding, converging evidence indicates that procedural memory—the system supporting sequence learning and automatization—also contributes to reading development. A meta-analysis of serial reaction time (SRT) studies demonstrated impaired procedural sequence learning in dyslexia, suggesting a domain-general learning deficit [10]. Behavioral experiments further revealed that children with developmental dyslexia exhibit impaired implicit sequence learning, particularly after extended practice and overnight consolidation [11].
More recently, longitudinal neuroimaging evidence has shown that such procedural learning deficits are accompanied by attenuated gray- and white-matter plasticity following SRT training [12]. Collectively, these findings suggest that inefficient engagement of procedural memory systems undermines automatization processes and, consequently, reading fluency.
Cognitive and Clinical Characteristics Including Positive Dyslexia
Dyslexia is most consistently characterized by deficits in phonological awareness (i.e., the ability to detect, blend, and manipulate phonemes within spoken words). These impairments directly disrupt the decoding process, in which graphemes must be systematically mapped onto their corresponding phonemes [2,12]. In addition, children with dyslexia frequently exhibit difficulties in rapid automatized naming (RAN), a skill reflecting the speed and efficiency of retrieving phonological labels for familiar stimuli such as letters, digits, or objects. Together, weaknesses in phonological awareness and RAN form the basis of the double-deficit hypothesis, which accounts for a significant proportion of individual variability in dyslexic reading difficulties [13].
Beyond these core deficits, broader weaknesses have been identified in working memory, reading fluency, and visual attention span. Importantly, these are not generalized impairments: children with dyslexia typically demonstrate normal nonverbal intelligence, intact oral language comprehension, and preserved higher-order semantic processing. Neurobiological studies suggest that the left temporo-parietal and occipito-temporal regions are primarily impaired at the level of grapheme-phoneme conversion and decoding, whereas the anterior and middle temporal lobes, which support semantic integration and comprehension, remain relatively unaffected [14]. This dissociation helps explain why many dyslexic individuals display strong verbal reasoning and oral comprehension despite severe decoding difficulties. In other words, dyslexia represents a domain-specific impairment in decoding skills rather than a generalized language disorder.
Clinically, dyslexia is also notable for its high rate of comorbidities. Epidemiological studies report that 25%-40% of individuals with dyslexia meet diagnostic criteria for attention deficit/hyperactivity disorder (ADHD), with shared vulnerabilities in attentional control and executive function contributing to this overlap [15]. Dysgraphia and developmental language disorder (DLD) also occur at elevated rates, further complicating assessment and intervention planning. The multiple-deficit model proposes that risk arises from interactions between phonological deficits and additional weaknesses in attention, processing speed, or motor coordination [16]. This model aligns with findings that, although decoding difficulties remain the core impairment, many individuals with dyslexia present a broader profile of cognitive vulnerabilities depending on their comorbid conditions.
Nevertheless, the relative sparing of higher-order language pathways carries important clinical implications. Once decoding is supported through intervention or compensatory strategies, individuals with dyslexia can leverage intact semantic and linguistic systems to achieve meaningful comprehension and learning. Intervention studies using phonological and fluency training have demonstrated not only behavioral improvements but also normalization of posterior reading network function on fMRI, thereby allowing dyslexic readers to access language systems that were never fundamentally impaired [17].
Although dyslexia is primarily defined by reading difficulties, recent research has increasingly emphasized potential cognitive strengths associated with the condition. Within the magnocellular-parvocellular framework, it has been proposed that while dyslexic individuals often exhibit impaired temporal processing within magnocellular systems, they may show a relative proliferation of parvocellular neurons, enhancing holistic and detail-oriented visual processing [18]. Supporting this hypothesis, empirical studies have found that individuals with dyslexia frequently outperform typical readers on tasks requiring global visuospatial perception, such as judging ‘impossible figures,’ detecting anomalies in visual patterns, and navigating complex environments [19].
In the auditory domain, similar advantages have been observed. Dyslexic individuals often demonstrate heightened sensitivity to timbre, harmony, and tonal coloration, even when rhythm processing is impaired. This perceptual profile may help explain anecdotal and case-based reports of dyslexic individuals excelling as musicians, artists, engineers, and entrepreneurs [20]. The concept of ‘positive dyslexia’ therefore highlights that the same neurobiological variations that hinder efficient decoding may simultaneously foster creativity, problem-solving capacity, and lateral thinking skills.
From a clinical perspective, acknowledging these strengths is essential. It reframes dyslexia not merely as a deficit but as a neurocognitive profile encompassing both vulnerabilities and assets. This broader perspective encourages educational and therapeutic interventions that not only target reading difficulties but also cultivate creativity and nonverbal talents, thereby enabling individuals with dyslexia to reach their full academic and personal potential [14,20].
Diagnosis and Assessment
The diagnosis of dyslexia is guided by internationally established criteria, including the DSM-5 and ICD-11, both of which emphasize persistent and significant reading impairments that are unexpected relative to a child’s age, cognitive ability, and educational exposure. A comprehensive evaluation is essential and typically includes standardized assessments of word reading, decoding, and spelling, as well as tasks measuring phonological awareness, reading fluency, and working memory.
Importantly, diagnostic assessment should not be confined to reading-specific skills. Broader evaluations of language and cognitive ability are necessary to distinguish dyslexia from other learning disorders. In addition, the identification of comorbid conditions such as ADHD, DLD, or dysgraphia is critical to capture the full clinical profile. Because dyslexia frequently co-occurs with attentional or emotional difficulties, a comprehensive neuropsychological evaluation is also recommended. Such evaluations should include intelligence testing to establish overall cognitive ability; attention and executive function testing to screen for ADHD or related vulnerabilities; and emotional and behavioral assessments, including measures of anxiety, depression, and self-esteem, as psychosocial difficulties often complicate academic adjustment. This multidimensional approach reflects the multiple-deficit model, which conceptualizes dyslexia as the result of interacting phonological, attentional, and emotional risk factors rather than a single isolated deficit [14,16].
In Korea, several standardized instruments are available for the diagnosis and screening of reading disabilities. Core diagnostic tools include the Korean Language-Based Reading Disability Test (KOLRA), the Reading Ability-Reading Comprehension Profile (RARCP), and the Comprehensive Learning Test (CLT), all of which assess overlapping domains such as phonological awareness, letter and word recognition, reading fluency, comprehension, and spelling. Additional instruments, such as the Early Reading and Math Test (ERAM), the Basic Academic Skills Assessment (BASA), and the Korean Learning Disability Evaluation Scale (K-LDES), provide further opportunities for early screening and multidimensional evaluation across developmental stages—from preschool literacy risk detection to formal diagnosis in school-aged children (Table 1).
Importance of Early Detection and Early Intervention
Early identification and intervention are critical determinants of long-term outcomes for children at risk of dyslexia. Neuroimaging evidence demonstrates that intensive reading interventions can induce measurable neuroplastic changes within the reading network. For instance, functional activation in the left occipito-temporal cortex (VWFA) has been shown to normalize following phonologically based remediation [17], while the structural integrity of white-matter pathways, particularly the AF and CR, improves after intensive intervention [21]. These findings support the view that early intervention coincides with a sensitive developmental period during which neural circuits underlying reading are most responsive to structured instruction. Intervention during this window is associated with substantially greater gains than remediation initiated later in schooling.
Cross-linguistic research further indicates that the manifestations of dyslexia differ depending on orthographic transparency. In transparent languages such as Finnish, Italian, or Korean, difficulties are most evident in reading fluency, whereas in opaque languages such as English or French, deficits in reading accuracy are more prominent [22,23]. These distinctions underscore the need for language-specific screening protocols, ensuring that early detection methods are tailored to the orthographic characteristics of each writing system.
Several early risk markers can be detected during the preschool years, often preceding formal literacy instruction. These include delayed speech onset, reduced vocabulary growth, difficulties in prosody and rhythm perception, and problems learning letter-sound correspondences (Table 2). Incorporating such indicators into teacher- and parent-report screening tools, supplemented by structured observational measures, enhances the accuracy of early identification. Effective early intervention also requires a multidisciplinary approach. Pediatricians, speech-language pathologists, educational psychologists, and special educators each play complementary roles in detection, diagnosis, and remediation. Primary care physicians, in particular, are well positioned to identify at-risk children during developmental surveillance by reviewing family history of dyslexia, monitoring language milestones, and referring for comprehensive assessment when necessary. Finally, early identification not only improves academic performance but also protects against secondary emotional consequences, including low self-esteem, anxiety, and depression. Children who receive timely intervention are more likely to maintain positive attitudes toward learning, whereas delayed diagnosis often leads to frustration and disengagement that exacerbate both academic and psychosocial difficulties [2,15]. Thus, early detection functions not only as an educational strategy but also as an essential component of mental health prevention, fostering resilience and promoting long-term well-being.
Treatment and Interventions
Explicit and systematic instruction remains the cornerstone of evidence-based intervention for dyslexia. Programs emphasizing phonological awareness and phonics, delivered through structured, multisensory methods such as the Orton-Gillingham approach, have repeatedly demonstrated effectiveness [2,15]. By integrating visual, auditory, and kinesthetic modalities, these interventions reinforce grapheme-phoneme mapping and progressively enhance decoding, spelling, and reading fluency. Their cumulative and systematic nature is particularly critical for children with dyslexia, who often fail to acquire these skills incidentally.
Technology and assistive tools provide important complementary support by improving accessibility and engagement. Text-to-speech software, audiobooks, and digital platforms allow children with dyslexia to access age-appropriate content while bypassing decoding barriers. More recently, AI-driven adaptive systems have been developed to personalize instruction and adjust pacing according to individual learning profiles, thereby promoting sustained motivation and participation. However, these tools should be implemented alongside, not in place of, explicit phonological instruction [24].
The intensity and consistency of interventions are decisive for long-term outcomes. Evidence shows that remediation must be intensive, systematic, and sustained to achieve meaningful gains [14]. Neuroimaging studies further demonstrate that such interventions can induce neuroplastic changes within the reading network, including normalization of activation in the left occipito-temporal cortex (VWFA) and improved structural integrity of white-matter pathways such as the AF and CR [17,21]. These findings underscore the importance of providing regular, long-term support, as children with dyslexia typically require more explicit and extended practice than their peers to achieve fluent reading. Equally critical is the expertise of the instructor. Interventions should be delivered by teachers or clinicians specifically trained in dyslexia-focused methodologies, as generic instruction often lacks the structured, diagnostic-prescriptive approach necessary for success. Schools must therefore ensure access to trained professionals and provide ongoing professional development opportunities to maintain instructional quality.
Regular re-evaluation and individualization are also essential. Because children with dyslexia vary in their rate of progress, ongoing assessments are recommended to monitor development, refine instructional goals, and prevent stagnation. Individualized education programs should incorporate these periodic evaluations and be collaboratively updated by teachers, parents, and clinicians [14]. Finally, effective intervention must address the emotional and family context. Sustained, intensive, and specialized support reduces the risk of secondary emotional problems such as anxiety, frustration, low self-esteem, and school disengagement. Active involvement of both teachers and parents provides encouragement, builds resilience, and fosters a positive learning identity. In this sense, treatment should be viewed not only as an academic intervention but also as a means of protecting mental health and promoting holistic development.
Conclusion
Developmental dyslexia is best conceptualized as a specific learning disorder with impairment in reading, characterized by persistent deficits in phonological awareness and decoding that lead to significant reading difficulties despite otherwise normal intelligence and educational opportunities. Advances in neuroimaging, genetics, and cognitive science increasingly reveal its multifactorial etiology, underscoring the necessity of comprehensive, multilevel approaches to diagnosis and intervention. Early detection and evidence-based interventions are central to improving both academic and socio-emotional outcomes. Screening and treatment strategies should therefore be integrated into primary care, educational practice, and national policy frameworks to ensure timely and equitable access to support. From a policy standpoint, it is crucial to incorporate teacher- and parent-report dyslexia screening tools into Korea’s National Health Screening Program for Infants and Children, as well as into routine school health checkups, targeting children from kindergarten through the early elementary years. Such integration would enable systematic early identification of at-risk children and facilitate timely intervention, thereby improving long-term educational and developmental trajectories. At the same time, improving public awareness of dyslexia is essential to reduce stigma and promote equitable educational opportunities. By combining scientific evidence, clinical expertise, and policy implementation, society can establish a comprehensive, lifespan-oriented support system that empowers children with dyslexia not only to overcome their reading challenges but also to thrive academically, emotionally, and socially. These considerations highlight the broader policy implications, emphasizing the need for early screening, structured literacy instruction, and public awareness initiatives to ensure equitable and sustainable support for individuals with dyslexia.
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