1.1.4 Genetic explanations: heritability
Did you know that dyslexia can run in families? Studies show it’s highly heritable, with a 40-70% chance (Gialluisi et al., 2021; Erbeli, Rice and Paracchini, 2021). For example, twin studies estimate heritability at 60-70% (Ciulkinyte et al., 2024). But finding the exact genes is tricky because each gene that has been related to dyslexia has a small effect, and they likely work together. Finding these genes is problematic because it needs very large studies, and past research hasn’t had enough data to clearly identify them.
DYX1C1 and oestrogen
The gene DYX1C1 is linked to dyslexia (Bates et al., 2010). Interaction with oestrogen (a hormone) has been seen to increase the expression of DYX1C1, suggesting a neuroprotective mechanism in females (Krafnick and Evans, 2019). Altarelli et al. (2013) note that some natural substances in our bodies (e.g. certain steroid hormones), along with other factors that aren’t hormone-related, could potentially make women’s brains more resilient to challenges.
Nature vs. nurture
According to the Dyslexia Research Trust (DRT), studies comparing identical and non-identical twins indicate that genetics account for about 50% of reading abilities, while the rest is influenced by environment. The gene KIAA0319, active early in brain development, affects areas crucial for reading.
Other studies mention DCDC2, GCFC2, MRPL19 and ROBO1 as being linked to dyslexia (Brkanac, 2007).
Shared genetic traits
Dyslexia, which is highly heritable, shares genetic links with other learning disorders like ADHD, dyscalculia, dyspraxia and others. Research indicates that genes linked to learning difficulties in one domain such as reading, are often connected to difficulties in another domain like math and some psychopathological disorders (Erbeli, Rice and Paracchini, 2021). Comorbidity is present in the genetic architecture of individuals who have a learning disorder, which is evidenced in different locations throughout the genome that is associated with these disorders and thus, can be somehow attributed to shared genetics influences (Georgitsi et al., 2021). Dyslexia, ADHD and dyscalculia often occur together because they share common genetic risk factors, rather than one causing the other.