Dyslexia

Dyslexia



Dyslexia is a learning disability that manifests itself as a difficulty with word decoding, reading comprehension and/or reading fluency. It is separate and distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with vision or hearing, or from poor or inadequate reading instruction. It is estimated that dyslexia affects between 5–17% of the population. Dyslexia has been proposed to have three cognitive subtypes (auditory, visual and attentional), although individual cases of dyslexia are better explained by the underlying neuropsychological deficits and co-occurring learning disabilities (e.g. attention-deficit/hyperactivity disorder, math disability, etc.). Although not an intellectual disability, it is considered both a learning disability and a reading disability.Dyslexia and IQ are not interrelated, since reading and cognition develop independently in individuals who have dyslexia.

Some shared symptoms of the speech/hearing deficits and dyslexia:

1. Confusion with before/after, right/left, and so on

2. Difficulty learning the alphabet

3. Difficulty with word retrieval or naming problems

4. Difficulty identifying or generating rhyming words, or counting syllables in words (phonological awareness)

5. Difficulty with hearing and manipulating sounds in words (phonemic awareness)

6. Difficulty distinguishing different sounds in words (auditory discrimination)

7. Difficulty in learning the sounds of letters (In alphabetic writing systems)

8. Difficulty associating individual words with their correct meanings

9. Difficulty with time keeping and concept of time

10. Confusion with combinations of words

11. Difficulty in organization skills

The identification of these factors results from the study of patterns across many clinical observations of dyslexic children.

Individuals with dyslexia can be gifted in mathematics while having poor reading skills. They might have difficulty with word processing problems (e.g. descriptive mathematics, engineering or physics problems that rely on written text rather than numbers or formulas).

Causes

Neuroanatomy

 Some individuals with dyslexia show less electrical activation in parts of the left hemisphere of the brain involved in reading, which includes the inferior frontal gyrus, inferior parietal lobule, and middle and ventral temporal cortex.

Genetics

Genetic research into dyslexia has its roots in the examination of post-autopsy brains of people with dyslexia. When they observed anatomical differences in the language center in a dyslexic brain, they showed microscopic cortical malformations known as ectopias and more rarely vascular micro-malformations, and in some instances these cortical malformations appeared as a microgyrus.

Abnormal embryonic cell formations in dyslexics found on autopsy have also been reported in non-language cerebral and subcortical brain structures.

Gene-environment interaction

Research has examined gene–environment interactions in reading disability through twin studies, which estimate the proportion of variance associated with environment and the proportion associated with heritability. Studies examining the influence of environmental factors such as parental education, and teacher quality have determined that genetics have greater influence in supportive, rather than less optimal environments. Instead, it may just allow those genetic risk factors to account for more of the variance in outcome, because environmental risk factors that affect that outcome have been minimized.

As the environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability. Animal models and measures of gene expression and methylation in the human periphery are used to study epigenetic processes, both of which have limitations in extrapolating to the human brain.[78]

Signs and symptoms

In early childhood, early symptoms that correlate with a later diagnosis of dyslexia include delays in speech, letter reversal or mirror writing, and being easily distracted by background noise. This pattern of early distractibility is partially explained by the co-occurrence of dyslexia and attention-deficit/hyperactivity disorder. Although each disorder occurs in approximately 5% of children, 25-40% of children with either dyslexia or ADHD meet criteria for the other disorder.

Dyslexic children of school age can have various symptoms; including difficulty identifying or generating rhyming words, or counting syllables in words (phonological awareness), a difficulty segmenting words into individual sounds, or blending sounds to make words,a difficulty with word retrieval or naming problems (see anomic aphasia),commonly very poor spelling,which has been called dysorthographia or dysgraphia (orthographic coding), whole-word guesses, and tendencies to omit or add letters or words when writing and reading are considered classic signs.

Signs persist into adolescence and adulthood with trouble with summarizing a story, memorizing, reading aloud, and learning a foreign language. Adult dyslexics can read with good comprehension, although they tend to read more