GENOTYPIC AND PHENOTYPIC HETEROGENEITY IN DYSLEXIA

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Continuation is proposed for three highly interrelated projects: (a) a longitudinal behavioral study of normal, reading impaired, and "at risk" samples which had been started in 1st grade, third grade, and kindergarten, respectively; (b) a family study of adult dyslexics (defined by childhood psychometrics), including their spouses, siblings, parents, and children, and using behavioral measurement of the phenotype for all subjects and electrophysiological measurement of the phenotype for probands and their children; and (c) an integrated multidimensional physiological and anatomical study of the dyslexic phenotype---using blood flow (rCBF), event related potentials (ERP), positron emission tomography (PET), and magnetic resonance imaging (MRI). These studies are intended to clarify: (a) the longitudinal course of normal and impaired reading, and the differentiation of these courses from each other, including the demonstration of phenotypic markers of emerging dyslexia distinct from attention deficit disorder, low intelligence, and related conditions, and the possible intra-linguistic subtyping of the dyslexic phenotype; (b) the familial transmission patterns of the phenotype and its component processes and related comorbid disorders such as ADHD. (c) converging evidence for an anatomical (temporal planum; and physiological (left temporal, left angular gyrus, left caudate) deficit as characterizing the dyslexic phenotype.