Reading Learning Disorder

Updated: May 27, 2016
  • Author: Eric R Crouch, MD; Chief Editor: Caroly Pataki, MD  more...
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Overview

Background

Learning disabilities, which include reading disabilities, are frequently diagnosed in children. Learning disabilities can occur for a variety of reasons and often require a multidisciplinary approach to address some of the more complex problems that can surround the diagnosis. Early diagnosis and referral to qualified educational professionals for evidence-based assessments and therapies offers the best chance for an improvement in quality of life. Learning disabilities are primarily language-based disorders; vision problems do not cause primary dyslexia or learning disabilities. Although there are some vision problems that can interfere with the development of vision, the neurodevelopmental issues surrounding learning disabilities generally involve other areas of neural processing. 

Diagnostic Criteria (DSM5)

In 2013, the American Psychiatric Association released the Fifth Edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM5). In this latest edition, specific learning disorder (SLD) is the umbrella term for mathematics, reading, and written expression disorders. It is now a single, overall diagnosis, incorporating deficits that impact academic achievement. Rather than limiting learning disorders to diagnoses particular to reading, mathematics and written expression, the criteria describe shortcomings in general academic skills and provide detailed specifiers for the areas of reading, mathematics, and written expression. The diagnosis requires persistent difficulties in reading, writing, arithmetic, or mathematical reasoning skills during formal years of schooling. [1]

Specific learning disorder with impairment in reading includes possible deficits in:

  • Word reading accuracy
  • Reading rate or fluency
  • Reading comprehension

Impediments to successful reading may be caused by one or more impairments to the 3 skills necessary for reading: (1) word decoding, as in dyslexia; (2) automaticity of letter and word recognition, but intact decoding of words, as in a reading fluency problem; and (3) understanding the meaning of words, when decoding and fluency function well, as in a reading comprehension disorder.

Dyslexia is an alternative term used to refer to a pattern of learning difficulties characterized by problems with accurate or fluent word recognition, poor decoding, and poor spelling abilities.

Dyslexia is traditionally defined as an unexpected difficulty learning to read despite adequate intelligence, motivation, and educational opportunities. Longitudinal studies have demonstrated an association between dyslexia and language delays. Children may also have developmental problems with either expressive language, receptive language, or both. Such children are more likely to developing reading disorders. Many children with difficulties with reading, expressive language, or receptive language can also develop behavior disturbances in the home or classroom. These behaviors may ultimately impact their psychosocial development.

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Pathophysiology

The precise mechanism by which dyslexia develops has not been completely elucidated and numerous theories have been advanced.

Visual perceptual problems

At the beginning of the 20th century, dyslexia was believed to be caused by defects in the visual processing system that reversed and transposed words and letters. This belief persists despite research over the past 30 years that shows children with dyslexia do not have an increased risk of poorer vision than the general population. Attempts to overcome these visual defects through various eye training exercises to improve visual perception of written letters and words has not proven effective in treating dyslexia, dyspraxia, or dyscalculia problems. [2]

The etiology of reading disorders has been shown to involve disruption of phonemic processing. Thus, ocular movements are generally not a contributing factor in dyslexic patients. Even with occlusion, dyslexia persists on testing and most dyslexic patients do not demonstrate impaired oculomotor control. Weak ocular dominance by synoptophore testing has been studied by Stein et al; however, ocular dominance therapy has not proved to be an effective treatment in resolving dyslexia. [3]  Although saccades can be altered in patients with dyslexia, patterns of eye movement are a symptom rather than a distinct cause of dyslexia. [4]  Improved reading can result in improved saccadic eye movements, but therapies directed at improving saccadic eye movements have not shown improvement in reading scores. [5]

The visual system involves cortical function in the occipital and subsequently occipito-parietal and occipito-temporal lobes. The process for deciphering of visual images begins in the retina, is transmitted via the optic nerve, and is ultimately processed in the brain. The processes of visual sequencing, visual perception, and memory do not cause dyslexia.

Phonetic processing

Communication of thought is the goal of all language skills. Psychological, educational, and brain research over the past 20 years has consistently shown that dyslexia is a deficit of language processing. Dyslexia involves deficient decoding of individual linguistic units, called phonemes, which are the smallest detectable sound in a spoken word. Poor abilities in any part of this process (eg, segmenting/blending, speed, memory) adversely affects overall reading ability. A child with dyslexia typically has problems with segmentation, the process of recognizing different phonemes that constitute words or with blending these sounds to make words. A problem with speed or with rapidly naming words or letters interrupts reading fluency. Additionally, visual sequential memory problems interfere with reading comprehension.

Phonemes are the building blocks of the linguistic system and critical to developing spoken language. Phonological processing areas in the brain must break words into phonemic units before an individual can identify, understand, store, or remember them. Phonemic processing occurs automatically, without the speaker or listener consciously processing the information. Speech requires blending the phonemes into complete words, and thus words are heard as seamless, with no breaks. Although the word cat may seem like a single sound, humans can segment it into the 3 component phonemes.

A morpheme is the smallest meaningful speech sounds. Phonemes and morphemes are the fundamental elements of the linguistic system and critical to developing spoken and written language. Graphemes, the smallest unit in written language, contain visual symbols to represent the spoken phoneme. Individuals with dyslexia evidence impaired phonological awareness and as a result cannot adequately pair the visually processed graphemes with their associated phonemes. [6]

Research has shown that reading directly reflects spoken language. The process of reading involves the perception of alphabetic script coded as phonemes (ie, each symbol represents a phoneme). A person must recognize the visual sequence of letters in a specific order and correlate with the proper phonology. An individual must be able to simultaneously segment the letters into sounds and then blend those sounds into words.

This process of associating a grapheme with its phoneme must occur fast enough for reading fluency, and the reader must also remember and retain the words read long enough to recall their meanings. Slow grapheme-phoneme processing appears to be the primary cause of dyslexic reading problems.

The most prominent current hypothesis regarding the neuroanatomic regions of phonological and visual processing is that atypical phonological processing in the prereading years leads to inefficient mapping during the development of reading. Thus, the atypical phonological processing disrupts the development of the functional specialization of the visual areas. The brains of individuals with reading disorders are organized somewhat differently and appear to process the phonological information in a less efficient, more diffuse manner.

Neurophysiology

Neuroimaging has demonstrated variations in the right temporoparietal-occipital region among patients with dyslexia. The specific asymmetries have been located in the angular gyrus and corpus callosum. The angular gyrus is located in parietal lobe, specifically Brodmann’s area 39, and is involved in language, cognition, and mathematics. This may, in part, explain the association between dyslexia and dyscalculia.

Postmortem studies have documented disorganized neuronal migration involving other areas, such as the thalamus, subcortical white matter, and parieto-occipital region. EEG studies have also demonstrated differences between patients with and without dyslexia. Neurologically, positron emission tomography (PET) scan studies suggest that phonological defects in reading strongly relate to decreased activity in the left perisylvian region, including the superior and medial temporal gyri. Additional functional imaging work indicates that anterior regions of the brain are activated during phonological or rhyming tasks.

In addition, the left temporo-occipital region, which is active during the automatic perception and processing of visually presented words in skilled readers, is also implicated in reading problems. A lack of word-specific responsiveness in this region is found in adults with reading impairment. Anatomical lesion analysis has shown that this region is necessary for rapid perception of word forms.

Genetics

Genetic and neurobiological research confirms psychological research in this area. Family studies show that a reading disorder is heritable, is found in clusters in families, and probably reflects autosomal dominant transmission. Research has shown a high familial incidence of dyslexia and concordance among both monozygotic and dizygotic twins. Thus far, research has identified 8 isolated genetic defects among dyslexic patients, and at least another 20 genetic conditions with normal intelligence levels but associated reading disabilities with dyslexic features.

Challenges to the existing paradigm view dyslexia as largely determined by genetic load with the additional perspective that expression of the phenotype is on a continuum with the disability on one end and intact reading skills on the other. Given increasing evidence that environment can modify expression of phenotype, the possibility is being explored that the genetic diathesis could be manipulated by enrichment experience to express the nonpathologic aspect of the dyslexia phenotype. [7]

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Epidemiology

Frequency

United States

The prevalence of specific learning disoder across the academic domains of reading, writing, and mathematics is 5%-15% among school-age children across different languages and cultures. [1] Children with delays can be diagnosed with attention deficit disorders, brain dysfunction, sensory integration issues, dyslexia, dyspraxia, and dyscalculia. On occasion, a child may have more than one condition present. Dyslexia accounts for the majority of learning disabilities. [8]   

Data from epidemiological studies indicate as many as 40% of all early elementary school students in the United States have some initial difficulty learning to read; however, many of these children ultimately develop normal reading proficiency. Among older elementary students, up to 15-20% of children have significant problems and demonstrate difficulty with reading fluency, comprehension, and spelling. [9] Developmental delays, emotional disturbance, inadequate education, and sensory disabilities can also lead to academic failures and delays and should be investigated.

Reading disorder rates show no racial differences. For approximately the past 30 years, public schools have included the intelligence quotient (IQ) as part of their assessment for severe reading problems. A learning disability has been defined as a significant discrepancy between a child's IQ and reading achievement score. For example, if a child has an IQ in the 50th percentile and a reading score in the 20th percentile, that child would be considered to have a reading discrepancy. Care should be taken with children with below-average IQ scores and poor reading performance, as such children can be misdiagnosed as reading disabled or delayed.

However, the 2004 version of the federal Individuals with Disabilities Education Act (IDEA) no longer requires states to use the discrepancy score criteria (eg, if the IQ is 20 points higher than the reading achievement score, the discrepancy is significant) to identify reading disabilities. All that is now required to identify a learning disability is a significant delay and a poor response to a reading intervention. How each state interprets this law in the public school is still being developed. Because states develop their own rules, some states may retain the discrepancy criteria.

Sex

Boys are 1.5 times more likely to be referred for reading problems. Although epidemiological studies in the past demonstrated roughly equal reading scores for girls and boys, more recent studies have demonstrated a wider variance in reading performance among male students. [10]

Language

Dyslexia can occur in any language. There have even been cases of differential dyslexia in which a child can be more dyslexic in one language than another. Dyslexia may be more prevalent in English-speaking countries.

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Prognosis

Children with learning disabilities can achieve academic success through a multidisciplinary approach that targets and manages the complex aspects associated with the condition. Children with learning disabilities can be challenging, and addressing the issues is not always simple. With appropriate accommodations and support, children with learning disabilities can achieve academic progress. Patient advocacy is important to ensuring the child's issues are appropriately addressed through an individualized educational plan (IEP).

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Patient Education

Children with concerns for learning disabilities, such as dyslexia, dyscalculia, and dyspraxia, should be referred for multi-disciplinary evaluation with emphasis on educational, psychological, neurodevelopmental pediatrics, and medical assessments.

Broad-based support in the school and home including individualized care and evidence-based therapies should be utilized in maximizing children's neurodevelopment. These interventions can be combined with neuropsychological and medical treatments as needed.

Children with learning disabiliites who are thought to have poor visual development or oculomotor control should be referred to an ophthalmologist with experience with pediatric patients. Routine vision screening assessments will not necessarily detect learning disabilties since vision problems are not a primary cause of dyslexia.

Primary care physicians should help coordinate the multidisciplinary approach and refer children for evidence-based treatments.

Educators should make accommodations for patients with learning disablities and assist them in receiving individualized support in their school systems.

 

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