Version May 2024
INTRODUCTION — Reading is critical to the academic, economic, and social success of children. However, many children complete schooling without achieving more than basic literacy. Pediatric clinicians are well positioned to identify children at risk for reading difficulties and children who have unexpected difficulties in learning to read. Early identification and timely intervention for such children improve long-term outcome.
The epidemiology, etiology, and pathogenesis of reading difficulty in children will be reviewed here. The clinical evaluation, diagnosis, and treatment or reading difficulty and general issues related to learning disabilities are discussed separately.
●(See "Reading difficulty in children: Clinical features and evaluation".)
●(See "Reading difficulty in children: Interventions".)
●(See "Specific learning disorders in children: Clinical features".)
●(See "Specific learning disorders in children: Educational management".)
NORMAL READING DEVELOPMENT — Literacy development is a process that begins in infancy and has a natural hierarchy of progression. Literacy develops in parallel with language, but in contrast to language, which is natural and inherent, reading is acquired and must be taught (table 1). (See "Emergent literacy including language development".)
The transition from prereading to reading skills usually begins when children enter school [1]. At this stage, children begin to associate written letters with sounds. They gradually learn to recognize all of the letters within a word and to map the letters onto the correct sound, a process called "decoding." With repeated exposure, and reading words in context, children are able to recognize certain words automatically.
The skills needed for normal reading encompass five domains [1-4]:
●Phonemic awareness – Ability to focus on and manipulate phonemes (the smallest units of spoken language) in spoken words.
●Phonics – Knowledge of relationships between letters and sounds and spelling-sound correspondence, which allows decoding of words. The English language is particularly difficult for beginning readers because it contains inconsistent mappings between letters and sounds [5].
●Sight word acquisition – Automaticity of reading words by sight without having to decode sound by sound; sight word acquisition facilitates reading efficiency and allows interpretation of homonyms.
●Vocabulary – The knowledge of word meanings.
●Comprehension – An active, intentional process where meaning is extracted from text [6]. Reading comprehension is influenced by the ability to decode and sight read, vocabulary, oral comprehension, and "executive function" (eg, higher order skills such as working memory and planning) [1,7]. When reading passages, children construct meaning from sentences, which they must remember as reading progresses; at the same time they must link the information that is read to their background knowledge to anticipate what comes next [3].
The "simple view of reading" conceptualizes reading as two-step process: The first involves decoding, in which written letters are translated into words; the second involves extracting meaning from words. Extracting meaning from words draws on the same skills required to understand spoken language – vocabulary, knowledge of grammatical structure, and the ability to make inference. Although reading is predominantly the product of word identification and reading comprehension, other factors such as rapid word identification and reading fluency play a role [8].
TERMINOLOGY AND CONCEPTUAL FRAMEWORK — A variety of terms are used to describe reading problems. Different terms may be used in different settings and by different groups (eg, educators, health care providers). Definitions for the terms that are used in this topic review are provided below.
Reading difficulty — "Reading difficulty" is defined from a normative perspective (ie, how a child performs in reading compared to peers or educational expectations) [9]. Reading difficulty has a number of causes, the two most important of which are reading disability (ie, difficulties in decoding) and deficits in reading comprehension. The relationship between decoding deficits and reading comprehension deficits is unclear; they are considered to be separate deficiencies [10]. Most children with reading difficulties have some degree of deficit in both decoding and reading comprehension. However, some children have isolated deficiencies in either decoding or reading comprehension [11,12].
Other causes of reading difficulty include environmental factors (eg, lack of exposure to books or reading, inadequate instruction), cognitive impairment, hearing impairment, language impairment, chronic illness, and psychosocial stressors [13]. (See "Specific learning disorders in children: Clinical features", section on 'Differential diagnosis'.)
Reading disability — Reading disability is best defined as "an unexpected difficulty in learning how to read despite adequate intelligence, instruction, and motivation" [9]. The terms "dyslexia," "developmental dyslexia," "specific learning disorder with impairment in reading," "specific reading disability," and "reading disorder" are also used to describe this condition, although a more specific definition for "dyslexia" is provided below [10]. Reading disability is the most common form of learning disability. (See "Specific learning disorders in children: Clinical features".)
Dimensional model — Reading ability and reading disability occur along a continuum. Children with reading disabilities represent the tail end of a normal distribution of reading abilities [14,15].
Discrepancy model — In practice, reading disability has been defined by reading skills that are 1.5 or more standard deviations below the intelligence quotient (IQ). This definition has been used for research purposes, and many states use it to determine whether a child qualifies for special education services [9].
However, definitions based upon IQ-achievement discrepancy are problematic for several reasons and have largely been replaced by dimensional models. Problems with discrepancy models include [5,15-19]:
●An arbitrarily defined cut-off. Children on one side of the cut-off do not differ in any qualitative way from those on the other side.
●Children with a similar level of reading difficulty share the same fundamental deficits and respond to the same interventions (regardless of IQ).
●Discrepancy definitions do not take into account the changing demands of reading over time.
●Because most intelligence tests contain items that depend upon knowledge and skills that are acquired through reading, they may underestimate intelligence in children with long-standing reading difficulties (and fail to identify them as reading disabled by the discrepancy definition).
Dyslexia — The term "dyslexia" is used as a synonym for a specific reading disability [5,20]. The International Dyslexia Association defines dyslexia as follows [21,22]:
"Dyslexia is a specific learning disability that is neurologic in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonologic component of language. The deficit is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede the growth of vocabulary and background knowledge."
This definition has been adopted by the United States National Institutes of Child Health and Human Development and is similar to the definition in The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) [10]. The DSM-5-TR describes dyslexia as a specific learning disorder with impairment in accurate or fluent word recognition, decoding, or spelling; additional deficits in reading comprehension are to be specified separately.
In the text that follows, "reading disability" is used synonymously with "dyslexia." Reading comprehension deficits are considered to be separate category of reading difficulty.
Reading comprehension deficit — Reading comprehension deficit refers to difficulty in deriving meaning from written text that cannot be fully explained by difficulties in decoding (ie, reading disability/dyslexia) [10]. Reading comprehension problems are an important cause of persistent reading problems and may be related to underlying language disorders or problems with executive functions [18,23].
Similar to decoding skills, reading comprehension skills are dimensional. Children with reading comprehension deficits represent the lower end of a normally distributed range of reading comprehension skills [18]. (See 'Dimensional model' above.)
EPIDEMIOLOGY
Reading difficulties — As many as 20 percent of children have significant difficulty learning to read [13]. According to the 2017 National Assessment of Educational Progress, approximately 30 percent of United States fourth graders read below a basic proficiency level [24].
Reading below the basic proficiency level is more common in males than in females in the United States (35 versus 29 percent among fourth graders and 28 versus 19 percent among eighth graders based on 2017 statistics) [24]. Reading difficulties are also more common in Black, Hispanic, Native Hawaiian/other Pacific Islander, and American Indian/Alaska Native children and children from low-income families [24]. The exact cause of these discrepancies is not known, but low parental literacy, inadequate instruction, and other social risk factors likely play a role.
Reading disabilities — Reading disability is the most common learning disability, accounting for approximately 80 percent of cases [25]. In the United States, the reported prevalence of reading disability ranges from 5 to 17.5 percent of school children, depending upon the definition [26-29]. Reading disability is more commonly diagnosed in males [24]. However, this probably reflects a referral bias [30-32].
Risk factors — Risk factors for reading difficulty include [20,33]:
●Family history of language, speech, or reading difficulties [34-37]. (See 'Genetics' below.)
●Personal history of speech and language impairment in preschool (more strongly associated with reading comprehension than phonologic deficits) [18,23,38,39]. Approximately 50 percent of children with a history of speech and language impairment develop a reading disability during the early school years [23]. Children receiving intervention (eg, speech and language therapy, Head Start programs) for identified risk factors remain at a higher risk of reading difficulties than other children [18,40,41]. (See "Reading difficulty in children: Clinical features and evaluation", section on 'Preschooler at risk'.)
●History of prematurity and low birth weight [42].
●Congenital or acquired brain injuries (eg, congenital infections, in utero substance exposure, meningitis, encephalitis).
●Certain genetic syndromes (eg, Down syndrome, Klinefelter syndrome). (See "Down syndrome: Clinical features and diagnosis" and "Clinical features, diagnosis, and management of Klinefelter syndrome", section on 'Clinical features'.)
●Environmental risk factors – Although environmental factors may be present in children with reading disability, they are generally not the primary cause. Factors other than socioeconomic status have been shown to determine 90 percent of the variance seen in reading skills [43]. Environmental risk factors include [13,44-46]:
•Lack of exposure to books and reading (home literacy environment)
•Inadequate instruction in prereading skills
•Poverty
•Low parental education
ETIOLOGY AND PATHOGENESIS OF READING DISABILITY — The major problem in children with reading disability is thought to be a deficit in phonologic processing [4,5,20,47-49]. Deficits in executive function (eg, working memory) may contribute to problems in reading comprehension [7]. Twin, molecular linkage, neuroanatomic, and neurophysiologic studies indicate that reading disability is a highly heritable trait with a neurobiologic basis [22,50-57]. The exact mechanisms through which genetic and neuroanatomic factors affect phonologic processing are not entirely clear but are beginning to be elucidated with functional brain imaging studies.
Phonologic deficit — Before learning to read, a child must understand that spoken words can be broken down into smaller units of sound (ie, phonemes) [58,59]. As an example, the word "cat" consists of the phonemes /k/, /a/, and /t/. As phonemic awareness is gained, the child understands that the letters in written words represent phonemes that create recognizable words when strung together. (See 'Normal reading development' above.)
This awareness that words, both spoken and written, can be divided into sound segments is difficult for many children to master [14]. Difficulty with phonemic awareness in prereaders is a strong predictor of future reading problems [60-63].
The phonologic deficit in reading disability is independent of nonphonologic abilities [20]. Higher-order cognitive and linguistic functions involved in comprehension (eg, general intelligence, reasoning, vocabulary, syntax) are not affected. However, the circumscribed phonologic deficit may block access to higher-order processes and the ability to draw meaning from the text. As an example, an individual who knows the definition of the word "apparition" will not be able to use that knowledge when presented with the written word unless the word can be decoded and identified [20].
Language impairment — Reading comprehension difficulties frequently are rooted in problems understanding spoken language [18,64-66]. Children who have problems with reading comprehension that cannot be fully explained by difficulties in decoding (ie, dyslexia) often have a history of specific language impairment, low vocabulary, and/or poor grammatical skills [23,67]. Extracting meaning from written words requires the same skills required to understand spoken language – vocabulary, knowledge of grammatical structure, and the ability to make inference. Reading comprehension deficits are an increasingly important cause of reading problems in older children as reading materials grow more complex as they proceed through school [68].
Executive function deficits — Executive function refers to higher-order and goal-oriented skills such as memory, capacity for inference, planning, and automatic self-monitoring. Deficits in executive functions are associated with difficulties in reading comprehension even when other known variables are controlled [7,8]. Executive function skills become more important as the length and complexity of the text increases. Whether deficits in executive function contribute to problems with phonologic awareness/word identification is unclear [7].
Genetics — Reading disability tends to cluster in families with genetic factors accounting for most of the variability [34,35,69]. Reading disability occurs with 70 to 80 percent concordance in monozygotic twins; the concordance in dizygotic twins is 40 to 50 percent, which is similar to that in non-twin siblings [5,70-73]. The risk of reading disability is 40 to 60 percent among children of affected parents; conversely, 25 to 60 percent of parents of a child with reading disability also meet criteria for reading disability (though they may never have been formally diagnosed) [5,74,75].
The genetic contribution to reading disorders almost certainly involves multiple genes that interact with various host and environmental factors to determine the extent of reading disability [76,77]. Strong evidence links reading disability with five chromosomal regions: 1p, 2p, 6p, 15q, and 18q; modest evidence links reading disability with 6q, 3p, 11p, and Xq [51,53,54,78-83]. Evidence is particularly strong for two genes located on chromosome 6p22 (DCDC2 and KIAA0319), which are thought to involve neuronal migration [83-85]. Both genes express messenger ribonucleic acid (mRNA) in regions of the brain known to be involved in reading, such as the temporal cortex and cingulate gyrus [86,87]. This is consistent with the abnormal neuroanatomy described below. (See 'Neurobiology' below.)
Several of the genes with the strongest evidence for a role in reading disability appear to be pleiotropic (ie, to have other phenotypic effects). This suggests that there may be a genetic basis for the relationship between reading disability and other neurodevelopmental disorders, such as attention deficit disorder and speech-sound disorders [86,88].
Neurobiology — Neuroimaging studies of individuals with reading disabilities demonstrate structural and functional alterations in the regions of the brain responsible for language that can be observed before the beginning of reading instruction [33,89,90]. Activation of these regions during functional brain imaging is associated with response to intervention for reading disability. Alterations similar to those in individuals with dyslexia have been demonstrated in at-risk prereaders <18 months [90-92].
Electroencephalogram (auditory evoked response) shows particular promise in its ability to predict reading problems. In observational studies, auditory evoked responses in young children (<3 years old) correlated with reading difficulty during school-age [93-97].
Role of vision problems — Reading disability is not a problem with vision [5,98]. Children with reading disability do not see letters or words backwards; they have difficulty connecting the letters to sounds [20]. Nonetheless, eye problems that might interfere with learning (eg, refractive error, strabismus) should be identified as early as possible [99-101]. Those that are correctable should be managed by an ophthalmologist [99]. (See "Vision screening and assessment in infants and children".)
"Irlen syndrome" is a proposed perceptual disorder that causes distortions when viewing text and contributes to reading difficulty. Both the disorder and the proposed intervention (colored "Irlen" lenses) are controversial, as discussed separately. (See "Reading difficulty in children: Interventions", section on 'Unproven therapies'.)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or email these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient education" and the keyword[s] of interest.)
●Basics topic (see "Patient education: Dyslexia (The Basics)")
SUMMARY
●Normal reading development – The skills needed for normal reading encompass five domains (see 'Normal reading development' above):
•Phonemic awareness
•Phonics
•Sight word acquisition
•Vocabulary
•Comprehension
●Reading disability – Reading disability (also called dyslexia) is an unexpected difficulty in learning how to read despite adequate intelligence, instruction, and motivation. (See 'Reading disability' above and 'Dyslexia' above.)
●Risk factors – Risk factors for reading disability include (see 'Risk factors' above):
•Family history of language, speech, or reading difficulties
•Personal history of speech and language impairment in the preschool years
•History of prematurity or low birth weight
•Congenital or acquired brain injuries (eg, congenital infections, in utero substance exposure, meningitis, encephalitis)
•Certain genetic syndromes (eg, Down syndrome, Klinefelter syndrome)
•Environmental risk factors (eg, lack of exposure to books and reading, inadequate instruction in prereading skills, poverty, low parental education)
●Etiology and pathogenesis – Reading disability is a heritable disorder with a neurobiologic basis. The mechanisms through which genetic and neuroanatomic factors affect phonologic processing are not entirely clear. (See 'Etiology and pathogenesis of reading disability' above.)
The major problem in children with reading disability is a deficit in phonologic processing (the ability to break down spoken and written words into units of sound). (See 'Phonologic deficit' above.)
Another common problem is a deficit in reading comprehension (the ability to derive meaning from written text). (See 'Language impairment' above and 'Executive function deficits' above.)
Reading disability is not a problem with vision. Children with reading disability do not see letters or words backwards. (See 'Role of vision problems' above.)
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