Developmental dyslexia: An update on genes, brains, and environments

The science of reading and developmental dyslexia has experienced spectacul ar advances during the last few years. Five aspects of this research are di scussed in the article. (1) The holistic phenomenon of reading is complex. Many lower-level psychological processes (e.g., phonemic awareness, phonolo gical decoding, ability to process stimuli rapidly and automatize this proc ess, memory, ability to recognize words) contribute to a single act of read ing. Conceptualizing the complex process of reading through its partly over lapping but partly independent components-which contribute to, but do not f ully explain, the holistic process of reading-provides an excellent model f or understanding complex hierarchies of higher mental functions. Those who master reading skills successfully and those who have difficulties doing so differ in a wide range of reading-related processes. The central deficit e xperienced by poor readers appears to be related to phonological processing (a complex hierarchy of functions related to processing phonemes), whereas characteristics of automatization processes seem to moderate the reading o utcome for people whose phonological skills are weak. (2) There are new dat a addressing models of dyslexia in languages other than English. The most f ascinating finding is that the model implicating phonological deficit as ce ntral to dyslexia, and the lack of ability to automatize as leading to trou bled reading, appears to be universal, regardless of the specific language. However, there is an interaction effect between the characteristics of a p articular language and the developmental model of dyslexia. In phonological ly more difficult languages (e.g., English): the most pronounced weakness a ppears to occur in phonological processing, whereas in phonologically easie r languages (e.g., German), the crucial role in the manifestation of dyslex ia is played by the lack of the skills needed to achieve automatization. (3 ) There is abundant evidence that reading (i.e., any single act of reading as well as reading as a holistic process) is "cooked" by the brain. Althoug h no unified brain map of reading has been developed, some specific areas o f the brain have been implicated in different reading-related cognitive pro cesses by different laboratories and on different samples. (4) Indisputable evidence has been accumulated suggesting the involvement of the genome in developmental dyslexia. As of now, specific regions of the genome have been identified as being intimately involved with a number of different reading -related processes. Today the field of developmental dyslexia is the only a rea of genetic studies of human abilities and disabilities in which linkage s to the genome have been robustly replicated in independent laboratories. (5) Finally, evidence suggests that developmental dyslexia might be only on e of the manifestations of a deep, underlying, anatomical syndrome. The com orbidity of developmental dyslexia with both internalizing and externalizin g behavioral disturbances, as well as with other learning disabilities, und erscores the need for wide-ranging cognitive and behavioral approaches in t he remediation programs offered to dyslexic children.