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What is dyslexia?
Dyslexia is a neurodevelopmental disorder that is characterised by slow and inaccurate word recognition. The other main type of reading difficulty is problems with reading comprehension (some children experience both of these two main types of reading difficulty).
Developmental dyslexia causes difficulties with accurate and/or fluent word recognition and spelling. Learning difficulties associated with dyslexia may be caused by:
- Visual problems through not being able to recognise shape and form.
- Reading speed, accuracy or comprehension.
- Phoneme segmentation (cannot see or hear the components and then put them together to create meaning and to spell the words).
- This is reading impairment following some form of brain insult in individuals with previously normal levels of reading ability.
- It is frequently associated with aphasia where patients will exhibit a type of dyslexia in keeping with their form of aphasia - eg, fluent aphasics will have difficulties understanding printed word meanings while non-fluent aphasics will have trouble with grammatical aspects of reading.
The WHO ICD-11 classifications provides the following definitions:
Developmental learning disorder is characterised by significant and persistent difficulties in learning academic skills, which may include reading, writing, or arithmetic. The individual’s performance in the affected academic skill(s) is markedly below what would be expected for chronological age and general level of intellectual functioning, and results in significant impairment in the individual’s academic or occupational functioning.
Developmental learning disorder first manifests when academic skills are taught during the early school years. Developmental learning disorder is not due to a disorder of intellectual development, sensory impairment (vision or hearing), neurological or motor disorder, lack of availability of education, lack of proficiency in the language of academic instruction, or psychosocial adversity.
Developmental learning disorder with impairment in reading is characterised by significant and persistent difficulties in learning academic skills related to reading, such as word reading accuracy, reading fluency, and reading comprehension. The individual’s performance in reading is markedly below what would be expected for chronological age and level of intellectual functioning and results in significant impairment in the individual’s academic or occupational functioning.
Developmental learning disorder with impairment in reading is not due to a disorder of intellectual development, sensory impairment (vision or hearing), neurological disorder, lack of availability of education, lack of proficiency in the language of academic instruction, or psychosocial adversity.
How common is dyslexia? (Epidemiology)
Dyslexia affects all kinds of people regardless of intelligence, ethnicity or social class. Prevalence estimates depend on definition but is estimated to be between 5% and 17% of school-aged children. Adult dyslexia affects about 4% of the population.
There is a relatively small but significant male predominance. However boys with dyslexia come to clinical attention more often than girls because of higher rates of comorbid disorders, including attention deficit hyperactivity disorder (ADHD).
As well as ADHD, dyslexia is also comorbid with language impairment (defined by problems in the development of structural language, including grammar and vocabulary) and speech sound disorder (inability to produce the sounds of the individual's native language accurately and intelligibly).
Genetic and neuroimaging research have revealed that dyslexia is heritable, with brain differences that are present even before reading instruction begins. A number of susceptibility genes have been suggested.
Symptoms of dyslexia (presentation)
Dyslexia often presents at about the age of 7 or 8 years as the child's difficulties become clear in the school setting. However, many children with dyslexia experience language delays and difficulties preschool.
Common signs of dyslexia include:
- Hesitant and inaccurate reading.
- Need to re-read materials to gain an understanding.
- Difficulty with sequences - eg, putting dates in order.
- Erratic spelling.
- Reversal of letters (occurs in all children but less frequently than in those with dyslexia).
- Auditory language problems or visual spatial problems, which may contribute to difficulties with reading and spelling.
- Inability to distinguish sounds or shapes on the page.
- Associated features include poor spelling and handwriting, and mathematical difficulties.
- Assessment is usually carried out by an educational psychologist following a referral from a parent or teacher.
- Standardised measures, such as the Wechsler Intelligence Scale for Children, are used to assess general intellectual ability. More specific tools (eg, the Dyslexia Early Screening Test for testing early years, the Dyslexia Screening Test and the Aston Index) are used.
- The educational psychologist then investigates whether a child does not understand the meaning of words (semantic difficulty) or cannot see or hear the components and then put them together to create meaning and to spell the words (phoneme segmentation).
- About half of those with dyslexia also have dyscalculia:
- Dyscalculia is defined as difficulty acquiring basic arithmetic skills that is not explained by low intelligence or inadequate schooling.
- About 5% of children in primary schools are affected.
- Dyscalculia does not improve without treatment.
- It is important to identify language difficulties or any hearing problems which may be the underlying cause or contribute to the reading and spelling difficulties.
- There is an overlap between ADHD and a reading disorder. Children with a reading disorder are twice as likely as other children to have ADHD and children with ADHD are twice as likely to have a reading disorder.
- Dyspraxia is more common in people with dyslexia.
- Short-term memory, mathematics, concentration, personal organisation and sequencing may be affected.
Treatment and management of dyslexia
Remediation should be intensive, begin as early as possible, and be tailored to the individual. Phonics-based treatments are most effective.
There are a number of educational methods that can help people with dyslexia overcome their difficulties with reading and writing:
- Children with dyslexia require specialist teaching; many schools now have specialist provision for dyslexic children.
- Providing supportive home and school environments is essential. Parents and teachers should be strongly encouraged to praise and support the child.
- Teaching should be multi-sensory (include visual, auditory, movement and tactile elements), as children with dyslexia learn better when they can use as many different senses as possible - eg, writing the letter in the air at the same time as saying the letter and its sound. Teaching should also be highly structured.
- Phonics: the sounds that the letters represent are emphasised so that the child gradually connects the visual pattern of words to the auditory pattern of words.
- Computers: many children with dyslexia find it easier to work with a computer than write in a book, with the additional benefit of using the spell checker. Computer software programs are available to teach phonemic recognition and can provide effective adjuncts to tutoring and classroom intervention.
- Eye checks: regular eye checks are particularly important for any child or adult who has difficulties with reading or spelling and who may be dyslexic. Eye problems do not cause literacy problems, but can be a contributory factor.
- Colour overlays: some people with dyslexia are light- or colour-sensitive (Meares-Irlen syndrome) - eg, bright sunlight or fluorescent light may cause particular difficulties, black print on shiny white paper may be uncomfortable for the eyes, whiteboards may be too shiny, pattern glare may also be a problem. Transparent colour overlay filters (eg, Irlen coloured overlay lenses) have been widely used to improve reading performance. It may also be helpful to have coloured paper for writing and adjust the colours and brightness on computer screens.
- A number of other educational methods have been studied - eg, exercise-based therapy, which remains controversial.[11, 12]
Complications of dyslexia
- Rates of behavioural problems, social maladjustment, anxiety, withdrawal, and depression are higher in children with reading disorders.
- Social problems may increase as children get older, as they fall further behind with reading skills.
- Although some compensation can occur over time, dyslexia is usually persistent and may have a severe effect on academic achievement.
- The effectiveness of treatment depends on the initial severity of the dyslexia. The earlier the intervention, the better the outcome.
- With appropriate intervention (speech and language therapy) and teaching, affected children with expressive phonological and vocabulary difficulties can achieve an adequate literacy level to function in society, although their reading abilities may still lag behind those of their peers.
- Outcomes for patients with expressive syntax difficulties are more mixed, and interventions for those with receptive language difficulties need more research.
- However, many people affected by dyslexia have good ability in lateral thinking and shine in many fields, such as the arts, creativity, design and computing.
Further reading and references
Wagner RK, Zirps FA, Edwards AA, et al; The Prevalence of Dyslexia: A New Approach to Its Estimation. J Learn Disabil. 2020 Sep/Oct53(5):354-365. doi: 10.1177/0022219420920377. Epub 2020 May 26.
Peterson RL, Pennington BF; Developmental dyslexia. Lancet. 2012 May 26379(9830):1997-2007. doi: 10.1016/S0140-6736(12)60198-6. Epub 2012 Apr 17.
Hulme C, Snowling MJ; Reading disorders and dyslexia. Curr Opin Pediatr. 2016 Dec28(6):731-735. doi: 10.1097/MOP.0000000000000411.
International Classification of Diseases 11th Revision; World Health Organization, 2019/2021
Habib M, Giraud K; Dyslexia. Handb Clin Neurol. 2013111:229-35. doi: 10.1016/B978-0-444-52891-9.00023-3.
Soriano-Ferrer M, Piedra Martinez E; A review of the neurobiological basis of dyslexia in the adult population. Neurologia. 2014 Nov 11. pii: S0213-4853(14)00172-8. doi: 10.1016/j.nrl.2014.08.003.
Sanfilippo J, Ness M, Petscher Y, et al; Reintroducing Dyslexia: Early Identification and Implications for Pediatric Practice. Pediatrics. 2020 Jul146(1):e20193046. doi: 10.1542/peds.2019-3046. Epub 2020 Jun 23.
Kere J; The molecular genetics and neurobiology of developmental dyslexia as model of a complex phenotype. Biochem Biophys Res Commun. 2014 Sep 19452(2):236-43. doi: 10.1016/j.bbrc.2014.07.102. Epub 2014 Jul 28.
Kaufmann L, von Aster M; The diagnosis and management of dyscalculia. Dtsch Arztebl Int. 2012 Nov109(45):767-77
Uccula A, Enna M, Mulatti C; Colors, colored overlays, and reading skills. Front Psychol. 2014 Jul 295:833. doi: 10.3389/fpsyg.2014.00833. eCollection 2014.
Reynolds D, Nicolson RI; Follow-up of an exercise-based treatment for children with reading difficulties. Dyslexia. 2007 May13(2):78-96.
Rack JP, Snowling MJ, Hulme C, et al; No evidence that an exercise-based treatment programme (DDAT) has specific benefits for children with reading difficulties. Dyslexia. 2007 May13(2):97-104
Demonet JF, Taylor MJ, Chaix Y; Developmental dyslexia. Lancet. 2004 May 1363(9419):1451-60.
Law J, Garrett Z, Nye C; Speech and language therapy interventions for children with primary speech and language delay or disorder. Cochrane Database Syst Rev. 2003(3):CD004110.