Purpose: The goal of this study was to investigate the etiologic basis for the association between deficits in phonological memory (PM) and vocabulary in school-age children. Method: Children with deficits in PM or vocabulary were identified within the International Longitudinal Twin Study (ILTS; Samuelsson et al., 2005). The ILTS includes 1,045…

Modern behavior-genetic studies of twins in the United States, Australia, Scandinavia, and the United Kingdom show that genes account for most of the variance in children's reading ability by the end of the 1st year of formal reading instruction. Strong genetic influence continues across the grades, though the relevant genes vary for reading words…

Reading disability (RD) and math disability (MD) frequently co-occur, but the etiology of this comorbidity is not well understood. Groups with RD only (N = 241), MD only (N = 183), and RD + MD (N = 188) and a control group with neither disorder (N = 411) completed a battery of measures of internalizing and externalizing psychopathology, social and…

Does the choice of test for assessing reading comprehension influence the outcome of genetic analyses? A twin design compared two types of reading comprehension tests classified as primarily associated with word decoding (RC-D) or listening comprehension (RC-LC). For both types of tests, the overall genetic influence is high and nearly identical.…

Genetic and environmental relations between vocabulary and reading skills were explored longitudinally from preschool through Grades 2 and 4. At preschool there were strong shared-environment and weak genetic influences on both vocabulary and print knowledge but substantial differences in their source. Separation of etiology for vocabulary and…

Longitudinal twin data were analyzed to investigate the etiology of the stability of genetic and environmental influences on word reading and reading comprehension, as well as the stability of those influences on their relationship. Participating twin pairs were initially tested at a mean age of 10.3 years, and retested approximately five years…

To test the hypothesis that the etiology of reading difficulties may differ for males and females in more severely impaired samples, reading performance data from monozygotic (MZ), same-sex dizygotic (DZ[subscript ss]), and opposite-sex dizygotic (DZ[subscript os]) twin pairs were analyzed using a model-fitting implementation of the DeFries-Fulker…

This study investigated the role of the myelin oligodendrocye glycoportein (MOG) gene to reading disability in 22 children with dyslexia and 96 random controls. Results suggest that, although alleles in the MOG gene may be in linkage disequilibrium with a locus that contributes to reading disability, the MOG gene itself is probably not involved.…

Numerous studies have examined the etiology of the association between reading difficulties and attention-deficit hyperactivity disorder (ADHD) in school-age children, but little is known about the relation between prereading skills and ADHD behaviors prior to the beginning of formal reading instruction. A population-based sample of 809 pairs of…

Examines the etiology of high reading ability in twin pairs. Suggests that reading ability and its cognitive correlates are on a continuous distribution, with both extremes of the distribution being similarly heritable. Supports the hypothesis that the same cognitive processes that are associated with dyslexia are important for the development of…

A study assessed genetic and environmental etiologies of reading, rapid naming (RN), and their covariation using data from 587 twin pairs (ages 7-20) in which one student had reading difficulties and from 360 control pairs. Correlation between reading and RN performances for subjects was significantly higher than that of controls. (Contains…

Composite reading performance data from 223 pairs of identical twins and 169 same-gender fraternal twins in which at least one member was classified with reading disability were subjected to multiple regression analysis. Results indicated that the genetic etiology of reading disability differs as a linear function of IQ. (Contains extensive…

Preliminary results from data on 146 Australian, 284 American, and 70 Norwegian preschool twins indicate reliable genetic influences on phonological awareness and memory and learning. Vocabulary, grammar, and morphology showed significant shared environment and negligible genetic effects. A print knowledge composite showed genetic and shared…