The central hypotheses of Research Project II are 1) that reading and writing are complex skills that depend on a number of component processes that have both shared and independent genetic and environmental etiologies in children with disabilities, and 2) that patterns of covariation in etiology will provide unique insights into the cognitive architecture underlying these skills and into the nature of learning disabilities. Project II is assessing component processes in reading, writing, and related language skills in twins and siblings selected for deficits in reading and/or ADHD, and in normal-range control twins. The broad age range of the sample allows us to assess developmental differences in skills and in the expression of disabilities across grades 2 - 12. Our long-running assessment of word recognition, orthographic coding, phonological decoding, and phonological awareness continues to support more powerful and informative behavioral and molecular genetic analyses of these skills, but our main emphasis is on the relations of these skills to reading fluency, reading and listening comprehension, writing, and higher-level language skills.
Univariate multiple regression (DF) analyses are being used to evaluate the genetic and environmental etiologies for deficits in each skill. Bivariate DF analyses and confirmatory factor analyses of twin data are being used to assess the genetic and environmental covariance among the different skills. Behavior-genetic analyses are also used to validate subtypes and/or dimensions of individual differences among children with reading and writing disabilities by assessing their differential genetic and environmental etiology. In collaboration with Research Projects I, III, and IV, QTL analyses are assessing genetic linkage and association for deficits in different reading, writing, and language skills.
In collaboration with Research Project III, we are exploring the relations of these deficits to different symptoms and cognitive components of ADHD. New and recently introduced measures included in Project II are supporting the first thorough analysis of genetic and environmental influences on component processes in reading fluency, reading comprehension, listening comprehension, and writing.
