Official websites use. Share sensitive information only on official, secure websites. Author for correspondence: Tel. Cross-country, longitudinal twin studies provide strong evidence for both the biological and environmental basis of dyslexia, and the stability of genetic influences on reading and spelling, even when skills improve in response to instruction. General principles for diagnosis and treatment, based on research with children who failed to respond to the regular instructional program, are summarized for children meeting research criteria for having or being at risk for dyslexia or dysgraphia.
Research documenting earlier emerging specific oral language impairment during preschool years associated with reading and writing disabilities during school years is also reviewed. Recent seminal advances and projected future trends are discussed for linking brain endophenotypes and gene candidates, identifying transchromosomal interactions, and exploring epigenetics chemic al modifications of gene expression in response to developmental or environmental changes.
Rather than providing final answers, this review highlights past, current and emerging issues in dyslexia research and practice. Keywords: brain imaging, childhood, chromosome linkage, dysgraphia, dyslexia, family genetics, gene candidates, oral and written language learning disability OWL LD , reading and writing disorders, specific language impairment. Behavioral genetic research with twins in the USA [ 1 , 2 ], England [ 3 ], Australia [ 4 ] and Finland [ 5 ] has clearly demonstrated both biological and environmental influences on reading disability [ 6 ].
Comparison of twins who share the same genes versus those who share, on average, only half their genes has shown in these cross-country, longitudinal studies that genetic influences on reading and writing are stable from the preschool years to grade 2.
Yet related instructional research has shown that children with dyslexia benefit from specialized, language-based instruction [ 7 ]. The exciting new finding in these cross-country twin studies is that new genetic influences emerge in grade 2 when curriculum requirements change relative to kindergarten, demonstrating that how genetic vulnerability expresses itself is a function of the nature of the instructional environment. In this article we address the current understanding of the genetic and brain indicators of dyslexia and their relationship to therapy.
