Dyslexia

Dyslexia, sometimes called word blindness, is a learning disability that impacts reading, writing, or speaking, with severity varying from person to person. Common challenges include spelling, reading quickly, writing words, mentally sounding out words, pronouncing words aloud, and understanding what has been read. These issues are usually first noticed in school. The difficulties are not voluntary, and individuals with dyslexia have a normal desire to learn. People with dyslexia are more likely to also have attention deficit hyperactivity disorder (ADHD), developmental language disorders, or trouble with numbers.

The condition is thought to arise from a mix of genetic and environmental influences, and it can run in families. When dyslexia results from a traumatic brain injury, stroke, or dementia, it is called acquired dyslexia or alexia. The underlying mechanisms involve differences in how the brain processes language. Diagnosis involves a series of tests for memory, vision, spelling, and reading skills. Dyslexia is distinct from reading problems caused by hearing or vision issues, poor teaching, or lack of learning opportunities.

Treatment focuses on adjusting teaching methods to fit the individual’s needs. While it does not cure the underlying condition, it can reduce the degree or impact of symptoms. Vision-based treatments are not effective. Dyslexia is the most common learning disability and occurs worldwide, affecting 3–7% of the population, though up to 20% may have some symptoms. It is diagnosed more often in boys, but this is partly due to referral bias among teachers and professionals; some believe it affects men and women equally. Some view dyslexia as a different way of learning, with both advantages and disadvantages.

**Classification** Dyslexia is divided into developmental and acquired forms. Acquired dyslexia follows neurological damage, such as from traumatic brain injury or stroke. People with acquired dyslexia show some signs of the developmental disorder but need different assessment and treatment. Pure alexia, also called agnosic alexia or pure word blindness, is a form of alexia within the “peripheral dyslexia” group.

**Signs and symptoms** In early childhood, symptoms linked to later dyslexia include delayed speech onset and a lack of phonological awareness. A common myth ties dyslexia to mirror writing or reading letters backward, but these behaviors are normal in many children learning to read and are not defining traits. School-age children may have trouble identifying or generating rhyming words, counting syllables, segmenting words into individual sounds (like the three sounds in “cat”), or blending sounds—all signs of reduced phonemic awareness. Difficulty with word retrieval or naming objects is also associated. People with dyslexia are often poor spellers, a feature sometimes called dysorthographia or dysgraphia, linked to orthographic coding skills. Problems continue into adolescence and adulthood, including trouble summarizing stories, memorizing, reading aloud, or learning foreign languages. Adults with dyslexia can often read with good comprehension but tend to read more slowly and perform worse on spelling tests or reading nonsense words.

**Associated conditions** Dyslexia often occurs alongside other learning disorders, though the reasons are not clear. These include: - **Dysgraphia**: Difficulty with writing or typing, sometimes due to eye–hand coordination problems; it can also hinder tasks like tying knots or repetitive actions. In dyslexia, dysgraphia is often multifactorial, involving impaired letter-writing automaticity, organizational and elaborative difficulties, and trouble forming visual word images for spelling. - **ADHD**: A disorder with problems sustaining attention, hyperactivity, or impulsivity. Dyslexia and ADHD commonly co-occur; about 15% (or 12–24%) of people with dyslexia have ADHD, and up to 35% of those with ADHD have dyslexia. - **Auditory processing disorder**: A listening disorder affecting how auditory information is processed, leading to issues with auditory memory and sequencing. Many with dyslexia have auditory processing problems and may develop their own logographic cues to compensate. Some research suggests auditory processing skills may be the primary deficit in dyslexia. - **Developmental coordination disorder**: A neurological condition marked by difficulty with routine tasks involving balance, fine-motor control, and kinesthetic coordination; trouble with speech sounds; and problems with short-term memory and organization.

**Causes** Researchers have sought the neurobiological basis of dyslexia since it was first identified in 1881. For instance, some have linked the common problem of not seeing letters clearly to abnormal development of visual nerve cells. Neuroimaging techniques are used to study these differences.