Dyslexia

Dyslexia is a specific developmental disorder some symptoms of dyslexia persist till adulthood .

Dyslexia is characterised by impairment of reading and spelling which cannot be explained by the delayed cognitive development.

Rather to the contrary believe children with dyslexia are not unintelligent.

According to The International Classification of Mental Disorders and the Diagnostic and Statistical Manual the disease can be diagnosed and ICD 10 also has criteria for Spelling Disorder.

SYMPTOMS 

Reading disorder is characterized by very significantly reduced reading speed. Children with reading disorder often require two to three times as much time as other children, or more, to read text. Slower reading leads to great difficulty understanding what has been read, particularly when reading longer sentences.

Associating individual letters with their correspond- ing sounds is very slow, and mistakes are often made. In place of words which are difficult to read, children with reading disorder tend to read other words with similar letters. Some children manage to deduce the content of a sentence on the basis of the other words it contains even when individual words are read incor- rectly (e.g. hammer instead of matter). It is therefore very important that diagnosis take into account not only reading comprehension but also the speed with which individual words are read aloud.

Limited reading speed is also the main symptom of reading disorder in adults (4). This occurs in particular with complex, polysyllabic, and rare words. In stressful situations, e.g. reading forms at an official office or in front of colleagues, symptoms increase. Reading disorder also manifests itself in counting (e.g. reading math word problems) and when learning foreign languages.

Spelling disorder is characterized by a significantly increased number of spelling errors. Children with spelling disorder usually spell only 10% of 40 test words correctly. In free writing, words are avoided when children suspect that they cannot spell them correctly. This is often perceived as limited vocabulary or a lack of linguistic ability. However, it is usually a compensation strategy to avoid spelling errors, which are still often corrected in red pen, with negative comments from teachers.

The development of the ability to spell comes in stages. First of all, children begin to spell phonetically, e.g. foto instead of photo or boks instead of box (Fig- ure 1). It usually takes a year to learn all sound-letter associations. Children with spelling disorder often take two years. The next stage of spelling development is orthographically correct writing.

Symptoms of reading disorder

Reading disorder is characterized by significantly reduced reading speed.

Symptoms of spelling disorder

Spelling disorder is characterized by a significantly increased number of spelling errors. Children with spelling disorder usually spell only 10% of the words in a writing-to-dictation task correctly.

CAUSES

Neuroanatomy

Neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), have shown a correlation between both functional and structural differences in the brains of children with reading difficulties. Some people with dyslexia show less electrical activation in parts of the left hemisphere of the brain involved with reading, such as the inferior frontal gyrus, inferior parietal lobule, and the middle and ventral temporal cortex. Over the past decade, brain activation studies using PET to study language have produced a breakthrough in the understanding of the neural basis of language. Neural bases for the visual lexicon and for auditory verbal short-term memory components have been proposed, with some implication that the observed neural manifestation of developmental dyslexia is task-specific (i.e., functional rather than structural). fMRIs of people with dyslexia indicate an interactive role of the cerebellum and cerebral cortex as well as other brain structures in reading.

The cerebellar theory of dyslexia proposes that impairment of cerebellum-controlled muscle movement affects the formation of words by the tongue and facial muscles, resulting in the fluency problems that some people with dyslexia experience. The cerebellum is also involved in the automatization of some tasks, such as reading. The fact that some children with dyslexia have motor task and balance impairments could be consistent with a cerebellar role in their reading difficulties. However, the cerebellar theory has not been supported by controlled research studies.

Genetics

Research into potential genetic causes of dyslexia has its roots in post-autopsy examination of the brains of people with dyslexia. Observed anatomical differences in the language centers of such brains include microscopic cortical malformations known as ectopias, and more rarely, vascular micro-malformations, and microgyrus—a smaller than usual size for the gyrus. The previously cited studies and others suggest that abnormal cortical development, presumed to occur before or during the sixth month of fetal brain development, may have caused the abnormalities. Abnormal cell formations in people with dyslexia have also been reported in non-language cerebral and subcortical brain structures. Several genes have been associated with dyslexia, including DCDC2 and KIAA0319 on chromosome 6, and DYX1C1 on chromosome 15.

Gene–environment interaction

The contribution of gene–environment interaction to reading disability has been intensely studied using twin studies, which estimate the proportion of variance associated with a person’s environment and the proportion associated with their genes. Both environmental and genetic factors appear to contribute to reading development. Studies examining the influence of environmental factors such as parental education and teaching quality have determined that genetics have greater influence in supportive, rather than less optimal, environments. However, more optimal conditions may just allow those genetic risk factors to account for more of the variance in outcome because the environmental risk factors have been minimised.

As environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability. Measures of gene expression, histone modifications, and methylation in the human periphery are used to study epigenetic processes; however, all of these have limitations in the extrapolation of results for application to the human brain.

Language

The orthographic complexity of a language directly affects how difficult it is to learn to read it. English and French have comparatively “deep” phonemic orthographies within the Latin alphabet writing system, with complex structures employing spelling patterns on several levels: letter-sound correspondence, syllables, and morphemes. Languages such as Spanish, Italian and Finnish have mostly alphabetic orthographies, which primarily employ letter-sound correspondence—so-called “shallow” orthographies—which makes them easier to learn for people with dyslexia. Logographic writing systems, such as Chinese characters, have extensive symbol use; and these also pose problems for dyslexic learners.

PATHOPHYSIOLOGY 

Most individuals who are right handed usually they have language centres of their left cerebral hemisphere is more developed. It has been seen that in Dyslexic individuals it’s not seen.

 A popular theory given is Dual Route Theory.

ASSESSMENT

• Strive for a multidisciplinary team approach involving the child’s parent(s) and teacher(s); school psychologist; paediatrician; and, as appropriate, speech and language pathologist (speech therapist); and occupational therapist.
• Possess a thorough familiarity with typical ages children reach various general developmental milestones (write first name; draw a square), and domain-specific milestones, such as phonological awareness (recognise rhyming words; identify the initial sounds in words).
• Avoid over-reliance on tests. Careful observation of the child in the school and home environments, and sensitive, comprehensive parental interviews are just as important as tests.
• Take advantage of the empirically supported “response to intervention” (RTI) approach, which “… involves monitoring the progress of a group of children through a programme of intervention rather than undertaking a static assessment of their current skills. Children with the most need are those who fail to respond to effective teaching, and they are readily identified using this approach.”

TREATMENT 

There are various strategies and support therapy. For dyslexia intervention with alphabet writing systems., the fundamental aim is to increase a child’s awareness of correspondences between graphemes and phonemes and to relate these to reading and spelling by teaching how sounds blend into words 

EPIDEMIOLOGY 

It has been estimated that prevalence of this disease is about 5% it can be as high as 17% in few population group.

SOURCE

1. Wikipedia- https://en.wikipedia.org/wiki/Dyslexia

2. Schulte-Körne G. The prevention, diagnosis, and treatment of dyslexia. Dtsch Arztebl Int. 2010 Oct;107(41):718-26; quiz 27. doi: 10.3238/arztebl.2010.0718. Epub 2010 Oct 15. PMID: 21046003; PMCID: PMC2967798.

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