Amaia Carrión Castillo defends thesis “Deciphering common and rare genetic effects on reading ability”
Children differ in how easily they learn to read. About 5 percent of children struggle to read, and when this challenge cannot be explained by other factors (e.g. ADHD, or lack of exposure to books), it can lead to a diagnosis of dyslexia. Twin studies have shown that identical twins are more similar than fraternal twins in their reading abilities, which indicates that reading ability is strongly influenced by our genes. Today, we still know very little about which genes play a role in developing this skill. In her PhD research, Amaia Carrión Castillo approached the genetic basis of reading ability using complementary, state-of-the-art strategies.
Common genetic variants are positions in our genome that vary in the general population and the least frequent forms, or alleles, are found in at least 10% of people. Each of these variants is expected to have a very small effect on the behaviour (as for example, reading), and could act as a risk factor. We expect the sum of these common risk variants to explain the majority of the genetic contribution to reading ability. Carrión Castillo investigated whether some of the common genetic variants that were previously proposed to affect dyslexia or reading-related traits were associated with reading-related scores in two new Dutch datasets. She found evidence of association that was stable across several educational time-points (7-12 years), while other associations differed between children and adults.
Our genetic make-up also contains rare genetic variation, which is not common in the general population. These variants are likely to have bigger effects on behaviour, and have the potential to explain how dyslexia is inherited in unusual families where this condition is very common, affecting about half of the family members. Which are these rare variants? Carrión Castillo studied two families in which dyslexia seems to be inherited as a Mendelian trait, using high throughput sequencing technologies that enabled her to screen virtually the entire genome for rare variants. The results pointed to a gene that could explain dyslexia in one of the families (SEMA3C), and is proposed as a new candidate gene., In the other family, her results suggest that the ‘simple’ inheritance pattern that we see may not always reflect one single genetic cause.
Further research, looking at even larger groups of people and other families with high rates of dyslexia is needed to confirm these findings and to discover additional relevant genes. The findings from this research provide new entry-points for future work bridging the gap between our genes and reading abilities.
- Amaia Carrion Castillo will defend her thesis on Monday, November 7 at 12:30 in the Aula of the Radboud University.
- The thesis appears in the MPI Series (no 114).