Dyslexia

Etiology

Dyslexia is hereditary; however, home literacy and the teaching quality strongly impact the child’s reading ability. Twin studies have shown that reading difficulties are highly heritable, and recent genetic studies have found several small genes that affect reading development.[2] These genes affect neuron migration, cortical morphogenesis, the outgrowth of neurites, and the structure and function of cilia.[1]

Epidemiology

Reading ability is very diverse in the population and varies vastly with education level. The diagnosis of dyslexia can be difficult, but a common criterion is a reading accuracy 1.5 standard deviations below the mean. Approximately 7% of the population has dyslexia and there is no race or sex predilection.[2]

Pathophysiology

The cerebellum is substantially active during the initial stages of the learning process. Structural and functional imaging has found differences in the cerebellum of those with dyslexia. These individuals were found to have reduced grey matter in the right lobule of VI. It was also found that this lobule has abnormal activity in patients with dyslexia when asked to name objects rapidly. It is important to note that the cerebellar disruptions in dyslexia are different than those found in autism spectrum disorder and attention deficit hyperactivity disorder (ADHD), suggesting that specific circuits lead to various symptoms.[3]

Postmortem imaging has showed decreased asymmetry of the left and right sides of the planum temporale, left perisylvian architectonic dysplasias, and neuronal ectopias.[1] Magnetic resonance imaging (MRI) scanning is used for in vivo studies. Functional MRI (fMRI) is currently being used to study the brain areas involved in performing certain tasks. fMRI testing has found that those with dyslexia have altered activations in the left temporoparietal regions and bilaterally in the frontal and occipital regions.[1]

History and Physical

Children with reading difficulties present differently depending on their age. Early intervention is essential to improving their outcome as most children with reading issues still present in the third grade continue to struggle throughout their formal education. Diagnosis is not typically made until formal reading education has been attempted, usually in the first grade.

At-risk preschoolers may present with:[4]

• Rhyming difficulty
• Confusing words that sound similar
• Trouble learning the names of letters

At-risk kindergarten and first graders may present with:

• Inability to learn letters[5] 
  • Strong predictor for reading ability[6]
• Unable to read words and difficulty spelling by the end of first grade[5] 

Second grade and beyond may present with:[7]

• Poor school performance
• Dislike of school
• Somatic dysfunctions when heading to school or before work is due

Children with reading disabilities will avoid reading; this will expose them to fewer words and increase their reading deficiency. The physical exam for patients with dyslexia should be standard with a focus on signs of other neurological, medical, or genetic causes of their impairment.

Evaluation

Due to the ability to diagnose dyslexia as early as preschool, early intervention is possible. One study found that if there is a familial risk, but the child develops the early ability to letter-name, then the risk of having dyslexia dramatically decreases.[2] Children who have poor letter-naming skills at 4.5 to 5.5 years of age but have good phonological awareness are also at a reduced risk of having dyslexia.[2] Dyslexia is complicated and is the outcome of many factors. Those with language difficulties at the end of preschool are at high risk, and this is when screening is most effective.[2]

These children should first be screened for hearing and vision impairment. Laboratory or imaging testing is not typically necessary for these children unless there are other factors influencing this decision that was found in their history and physical examination. fMRI is used for research purposes and not for a diagnosis.

Children suspected of dyslexia should be referred for evaluation by the school system. Their reading ability, executive function, and intelligence quotient (IQ) will be tested. This testing, in the United States, is free and is typically required before services can be rendered.

Treatment / Management

As a clinician, it is crucial to work with parents, schools, and caregivers to identify patients with dyslexia early. However, most treatment is provided at school and at home. Early intervention will focus on vocabulary, comprehension, and necessary skills such as phonics. As students progress through their education, the intervention will move to improve understanding of word meanings, improved comprehension, more challenging reading, and strategies to excel.[8](A1)

Differential Diagnosis

• Hearing impairment
• Vision impairment
• Educational deficits
  • Decreased exposure
  • Increased absences
  • Poor instruction
• Cognitive impairment
• Learning disabilities
• Toxin exposure (lead poisoning)
• Familial dysfunction
• Emotional illness

Prognosis

Those with reading difficulty that is overcome during early education typically develop average reading skills. Those children who have a persistent reading deficit may become proficient in reading words in their area of interest. A longitudinal study has found that reading disabilities improve with age, but a gap may remain when compared to their peers.[9]

Complications

• Poor school performance
• Dislike of school
• Somatic dysfunction
• Social maladaptation
• Psychiatric illness (anxiety, depression)