Overview

Dyslexia is a common learning difficulty affecting a person's ability to read, write and spell. Along with these skills, dyslexia targets information processing, where dyslexic people may have trouble processing and remembering information they see and hear which affects their literacy, and sometimes organisational skills. The difficulty in relating speech sounds to letters and words is referred to as decoding, typically present in children.¹ 

It is a common misconception that dyslexia primarily affects children. In fact, people of all ages can be diagnosed with learning difficulty, with many recognising signs of dyslexia and diagnosed in their later adult years. In the UK, an estimated 1 in 10 people have some degree of dyslexia.

Dyslexia is a learning difficulty, rather than disability. This means that it is not caused by problems with hearing, vision or intelligence, but rather by differences in how the brain processes language. Although a lifelong problem that can cause challenges to daily activities and academic performance, many children diagnosed with dyslexia are able to succeed in their education, aided by specialised tutoring and emotional support. 

There is no cure for dyslexia, therefore understanding and having awareness of its causes and symptoms allows for early identification and management, ensuring a better quality of life for those affected. 

This article will delve into the causes of dyslexia, comprising genetic, neurological and environmental factors. Continue reading to also understand the symptoms you can look out for during early childhood, school-age and teenage to adult years. 

Causes of dyslexia

The exact causes of dyslexia are unclear. However, studies have demonstrated the role of genetic, neurological and environmental factors in developing the condition.

Genetic factors

Family history

Dyslexia is highly heritable and runs in families, indicating that genetics are an important factor in determining your reading and writing skills. This is sometimes referred to as developmental dyslexia. Family studies have shown that children with a dyslexic parent have an estimated 45% risk of inheriting the condition themselves in comparison to those who do not.^1,2 

There have been several twin studies establishing the heritability of dyslexia. Studies comparing genetically identical twins to fraternal twins (who are genetically no more similar than regular siblings) showed that there is a significant 40-70% increase in developing dyslexia if you are an identical twin.² Twin studies have also proven the increased heritability of some learning difficulties associated with dyslexia, such as:²

• 46-52% increase in rapid automatised naming (RAN) which is how quickly individuals can name objects, colours, pictures or symbols
• 62-68% increase in letter-word knowledge, word decoding, reading comprehension and reading
• 80% increased heritability in spelling
• 34% increased risk in language skills

Genes linked to dyslexia 

Twin studies helped to identify gene variants which were linked to dyslexia and reading ability. The specific genes with an established link to the learning difficulty include:

• KIAA0319 - This gene is important during early brain development. Underexpression of this gene influences neurodevelopmental processes which can cause complexity in reading and impaired phonological processing³
• ROBO1 - This gene is a neuronal axon guidance receptor gene involved in brain development. Variations in this gene are associated with reading difficulties and language processing⁴
• DCDC2 - Variations in this gene have been associated with reading and spelling difficulties 

Neurological factors

Dyslexia is a neurological condition, which means the problem is located in the brain and people with the condition are sometimes referred to as “neurodivergent”. This is because dyslexic people have differences in their brain structure and function. 

Those with dyslexia have a different distribution of metabolic activity in the brain compared to those without reading difficulties. 

Brain anatomy and function in relation to dyslexia

The brain can be divided into the left and right hemispheres, where dyslexia is associated with failures in function of the left side of the brain. The left side of the brain is responsible for reading, speech and language processing.⁵ 

People without dyslexia think predominately with the left side of their brain. However, due to impaired function of the left hemisphere, dyslexics use the right side of the brain to process information which is why they are commonly said to think differently. The right hemisphere is responsible for traits such as creativity, rhythm and intuition. 

Structural changes found in the left side of the brain associated with dyslexia include a reduction of neuroplasticity which is the brain's ability to change and adapt with experiences. This targets the language processing areas located in the left region of the brain:⁴

• Broca’s area - Located in the frontal region of the left side of the brain, containing neurons which are involved in speech production
• Wernicke’s area - This region of the brain contains motor neurons responsible for speech comprehension

The brain comprises of two types of material:

• Grey matter - Composed of nerve cells with the primary function of information processing. Grey matter is what is typically seen when looking at brain scans
• White matter - Composed of connective fibres coated in myelin to aid communication between nerves and responsible for transferring information around the brain. White matter is located in deeper parts of the brain

Those at risk of dyslexia have been found to have decreased grey matter in the left side of the brain which may lead to issues in processing language. Reduced grey matter observed in the cerebellum is linked to poor motor control and cognitive functions.⁶ Additionally, many people may have reduced white matter which is linked to a decreased reading skill.⁵ 

Environmental factors

Environmental factors play a crucial role in the development of dyslexia, especially in the developing brain of children. 

Prenatal and perinatal influences

Poor maternal health during pregnancy has been shown to negatively impact foetal brain development and increase the risk of developmental dyslexia, including:⁷

• Drug use
• Alcohol use
• Smoking tobacco
• Malnutrition
• Infectious diseases 

Complications arising during birth may increase developmental dyslexia by causing neurological impairments, such as:⁷

• Premature births
• Poor birthing conditions 
• Neonatal asphyxia (lack of oxygen in the womb during, after and before birth) 
• Low birth weight

Early language exposure and education

Children in a language-rich environment tend to develop stronger language skills as they engage in conversations and reading. 

Educational factors that may influence a child’s risk of developing dyslexia include:⁸

• Little exposure to reading materials and spoken language can hinder phonological development
• Parental involvement in their child’s education, such as supporting home learning and reading with them. A poor family environment can decrease literacy skills and may be caused by work commitments, poor parental literacy or lack of knowledge 
• Good quality of early education helps children develop their literacy skills. Employing ineffective teaching methods could increase the risk of dyslexia. This includes effective teacher training to identify dyslexia in children early on
• Children from a lower socioeconomic status may face challenges with access to educational resources and books, decreasing cognitive function and increasing language and literacy development. Studies have shown that children from low socioeconomic backgrounds read below grade-level proficiency⁹

Symptoms of dyslexia

Dyslexia can be diagnosed at any stage of life, with symptoms appearing differently depending on your age and the severity of the condition. The signs can be difficult to recognise, particularly in children. However, the condition can often become noticeable once children start reading. 

Early childhood symptoms

Indicators of dyslexia in early childhood often include:¹

• Delayed speech compared to other children
• Difficulty with pronunciation, such as reversing sounds in words or confusing words that sound similar 
• Delay in learning new words 
• Difficulty remembering numbers, colours and letters
• Problems learning and recognising rhyming words and nursery rhymes
• Finding it hard to carry out more than one instruction at a time

School-age symptoms

Dyslexia may become apparent during school, for example:⁹

• Reading below the expected level for their age
• Reading errors such as mispronouncing words and reversing letters, for example “d” and “b” or “p” and “q”
• Problems forming answers to questions 
• Difficulty remembering spelling patterns and rules 
• Being unable to see and hear similarities and differences in letters and words
• Spelling difficulties, such as consistent incorrect spelling and spelling mistakes
• Writing difficulties, including grammar and punctuation mistakes and putting thoughts into writing
• Spending a long time completing reading and writing tasks
• Struggles with mathematics, such as understanding symbols, numbers and simple arithmetic 

Teenage and adult symptoms

Signs of dyslexia can appear later in life and are similar to that in children. Some evident symptoms in teenagers and adults can include:

• Avoiding reading tasks 
• Labour-intensive and slow reading and writing 
• Problems reading aloud and mispronouncing words
• Frequent spelling and grammar mistakes 
• Disorganisation due to difficulty organising tasks
• Finding it difficult to keep up with conversations due to slow processing speed
• Difficulty completing mathematical word problems
• Difficulty maintaining focus and attention when completing literacy tasks

When to see a doctor

Untreated dyslexia can have negative long-term educational, social and economic implications on people of all ages. It is vital to speak to your doctor if you believe that you or your child may be showing signs of dyslexia. Particularly in children, if dyslexia is undiagnosed and unmanaged, it can continue into adulthood and prevent them from reaching their full potential. 

FAQ’s

What are the main symptoms of dyslexia?

The main symptoms of dyslexia are; 

• Difficulties in speaking, spelling words, pronouncing and reading
• Difficulties in solving maths-based problems
• Difficulties in concentration, focus and listening

Is dyslexia a form of autism?

Autism and dyslexia are both classified as learning difficulties and symptoms of both conditions may overlap, however, autism is considered a neurodevelopmental disorder whereas dyslexia is considered a specific learning difficulty.

Summary

• Dyslexia is a learning difficulty that affects an individual's reading, writing and spelling skills
• Studies show the condition is hereditary with a 45% risk of children developing the condition if they have a dyslexic parent. Several twin studies have shown that mutations and expression of specific genes can compromise reading and language processing 
• It is a neurological condition where differences in brain structure and function cause impaired function of the left side of the brain, which is responsible for literacy
• Environmental factors such as prenatal (before birth) and perinatal (after/during birth) influences and quality of education and early language exposure can increase the risk of dyslexia
• Symptoms can arise in early childhood, during school age and from teenage to adult years. Some common signs include delayed speech, mispronouncing words, reading errors including confusing letters, reading and writing difficulties, spelling mistakes and struggling with mathematics