~Dyslexia is a learning disorder that causes difficulty in reading or interpreting words. Children with dyslexia have problems relating speech sounds to letters.
~ Genetics research shows that changes in how neurons migrate in the brain are linked to dyslexia.
~ Early life stressors may combine with genetic variants to increase the risk of dyslexia.
This article digs into what researchers have learned about dyslexia by examining the genes that are likely to be altered in kids with dyslexia.
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Is Dyslexia Genetic?
Dyslexia is known to run in families. Heritability, or the genetic component, is estimated to be about 50%.
This means that genetics plays a big role in susceptibility to dyslexia but that there are also other factors involved. Researchers have found many different genetic variants that add a little to the risk of being dyslexic, showing that dyslexia is influenced by multiple genes instead of just one ‘dyslexia gene’.
Researchers estimate that 5 – 12% of individuals are affected by dyslexia. It is diagnosed in childhood and mainly occurs in children with normal or above-average IQ.[ref]
What is going on in the brain with dyslexia?
Genetic studies can help to point to the physiological cause of dyslexia. Two of the genes (KIA/A0319 and DCDC2) identified as playing a role in dyslexia are involved in neuron migration. A recent study (Oct. 2016) points to a connection between these genes and cilia, hair-like structures that are present in most neurons.[ref]
In other words, physical changes in the neurons happen in some people with the identified genetic variants. Not everyone with the variants will end up having dyslexia, though. Instead, it is a risk factor that seems to need another component.
It isn’t all genetics… environmental factors matter too.
A recent study looked at the interactions between genetics and environment in children with dyslexia combined with ADHD. The study found that one of the DCDC2 gene variants is associated with dyslexia and ADHD. Environmental factors also came into play: smoking in the home added to the correlation.[ref]
Other environmental factors that interact with genetics in increasing susceptibility may include:[ref][ref][ref]
- birth weight
- socio-economic status
- maternal smoking during pregnancy
- gestational iodine deficiency
- early life stressors
Note that all of those environmental factors cause stress, either physical or mental, in the baby or child.
Stress and the cortico-limbic system
Recent research points to the important role of chronic early-life stress on dyslexia. The brain has a vast potential to change and respond to environmental circumstances. These changes can occur in utero – but the brain is capable of changing throughout life. The biggest times of brain growth are early childhood years.
Stress – whether physical or mental – causes physiological changes. Hormones, including cortisol, can release due to stressors and affect the brain. The Hypothalamic-Pituitary-Adrenal (HPA) axis is the pathway linking stress hormones released from the adrenals and their effects on the brain.[ref]
Researchers hypothesize that early life stress causes physiological changes in the brain. In children with certain KIAA03190 genetic variants, maternal stress during pregnancy was linked with significantly poorer reading ability.[ref]
Not all stress is bad, of course. At a moderate level and intermittent, stress increases attention, motivation, and neuronal synaptic plasticity. However, chronic or excessive stress causes cellular metabolic changes that could shift the brain from growth and plasticity toward stress protection.[ref]
Dyslexia Genotype Report:
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Please note that most of these SNPs are not found in 23andMe v5 data, so if you aren’t seeing your data below, that may be the reason.
The KIAA0319 gene encodes a protein involved in cell-to-cell interactions. In animal models, knocking out the KIAA0319 gene causes animals to have impaired, rapid auditory processing and spatial learning problems. Most of these fairly common variants are found in a quarter of the population or more. Thus, they don’t cause dyslexia alone but rather increase the susceptibility to it.
Check your genetic data for rs4504469 (23andMe v4; AncestryDNA)
- T/T: protective against dyslexia in Asian populations, but linked to a higher risk of dyslexia in European populations.[ref][ref]
- C/T: protective against dyslexia in Asian populations, but linked to a higher risk of dyslexia in European populations.
- C/C: typical
Members: Your genotype for rs4504469 is —.
Check your genetic data for rs9461045 (23andMe v4; AncestryDNA):
- T/T: reduced expression of the KIA/A0319 gene, associated with a risk for dyslexia[ref]
- C/T: reduced expression of the KIA/A0319 gene, associated with a risk for dyslexia
- C/C: typical
Members: Your genotype for rs9461045 is —.
Check your genetic data for rs2038137 (23andMe v4):
- T/T: slightly increased risk of dyslexia[ref]
- G/T: typical risk
- G/G: typical risk
Members: Your genotype for rs2038137 is —.
Check your genetic data for rs761100 (23andMe v4, v5; AncestryDNA):
- C/C: slightly higher risk of dyslexia[ref]
- A/C: typical risk
- A/A: typical risk
Members: Your genotype for rs761100 is —.
Check your genetic data for rs6935076 (23andMe v4, AncestryDNA):
- T/T: slightly increased risk of dyslexia (OR = 1.25)[ref]
- C/T: slightly increased risk of dyslexia (OR = 1.25)
- C/C: typical
Members: Your genotype for rs6935076 is —.
The DCDC2 gene encodes a protein important in forming neurons in the brain.
Check your genetic data for rs793862 (23andMe v4; AncestryDNA):
- A/A: 3 to 5x greater risk of dyslexia[ref]
- A/G: increased risk of dyslexia
- G/G: typical risk
Members: Your genotype for rs793862 is —.
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