Dyslexia is an interesting example of the intersection between an evolved behavior (language) and a cultural invention (literacy). While there cannot be genes for reading or other relatively recent cultural inventions (consider agriculture, banking, and football), there can be genetic influences on evolved cognitive and behavioral traits necessary for proficiency in such cultural inventions. Because there is now extensive evidence of genetic influences on individual differences on most domains of cognition and behavior, it is not surprising that there are genetic influences on reading and spelling skills.
Dyslexia can be defined as a relatively severe difficulty in learning to recognize printed words, which is not explicable in terms of obvious intellectual or sensory impairments (for more discussion of detailed issues to do with the definition see Snowling, 2000b, and Vellutino & Fletcher, this volume). In what follows, we will first provide a brief history of the genetics of dyslexia, and then discuss the dramatic advances that have occurred in the last two decades using both behavioral and molecular approaches, and close with a discussion of how these approaches are being used to analyze the comorbidities of dyslexia. The goal is to provide an overview of this rapidly evolving field and to direct the reader to more detailed reviews of the findings, methods, and issues covered here. Earlier reviews of the genetics of dyslexia include Finucci (1978), Pennington and Smith (1983), DeFries and Gillis (1993), and Schulte-KΓΆrne (2001).
Brief History
Clinicians have known for a long time that dyslexia runs in families. Soon after developmental dyslexia was first described by Pringle-Morgan (1896) and Kerr (1897), several reports of familial aggregation appeared (Fisher,