And thanks to a large population study, evidence has become more compelling that two particular genes contribute to dyslexia. The link between dyslexia and one of these genes was even stronger when subjects had attention-deficit/hyperactivity disorder or a developmental language disorder as well as dyslexia.
More information about this study can be found in Psychiatric News at http://pn.psychiatryonline.org/content/46/12/19.full.
And more information about dyslexia in general can be found in a book published by American Psychiatric Publishing called Learning Disabilities - Implications for Psychiatric Treatment. See http://www.appi.org/SearchCenter/Pages/SearchDetail.aspx?ItemId=8383.