The contribution of gene–environment interaction to reading disability has been intensely studied using twin studies , which estimate the proportion of variance associated with a person's environment and the proportion associated with their genes. Studies examining the influence of environmental factors such as parental education  and teacher quality  have determined that genetics have greater influence in supportive, rather than less optimal, environments.  However, more optimal conditions may just allow those genetic risk factors to account for more of the variance in outcome because the environmental risk factors have been minimized.  As environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability. Animal experiments and measures of gene expression and methylation in the human periphery are used to study epigenetic processes; however, both types of study have many limitations in the extrapolation of results for application to the human brain. 
10. They misspell many words - especially simple one syllable words such as those on the Dolch List or Service word list. Conversely they often are able to spell words that are longer more complicated words. These words are usually connected to specific things or ideas they have interest learning about. They are often nouns which they can picture in their minds. We had one student who could not spell the simple words but could spell volcano, magma, mantle and lava because he had enjoyed learning about volcanoes and was able to connect the words to real things he could visualize and think about. It's hard to visualize the words "the, again, simple, from" which is important for a Dyslexic to remember the spelling of the words.