Behavior Genetics

, Volume 32, Issue 3, pp 181–198

Differential Genetic Etiology of Reading Component Processes as a Function of IQ


    • Department of PsychiatryWashington University School of Medicine
  • Shelley D. Smith
    • University of Nebraska Medical Center
  • Lon Cardon
    • University of Oxford
  • Bruce Pennington
    • University of Denver
  • Javier Gayan
    • University of Oxford
  • Richard K. Olson
    • Institute for Behavioral GeneticsUniversity of Colorado
  • John C. DeFries
    • Institute for Behavioral GeneticsUniversity of Colorado

DOI: 10.1023/A:1016069012111

Cite this article as:
Knopik, V.S., Smith, S.D., Cardon, L. et al. Behav Genet (2002) 32: 181. doi:10.1023/A:1016069012111


Results obtained from previous studies of word recognition, reading component skills, and reading composite measures suggest that genetic factors may be more important as a cause for reading disability among children with higher IQ scores than among those with lower IQ scores. To investigate the genetic etiology of reading disability further, measures of word recognition, phonological decoding, orthographic coding, and phoneme awareness were obtained from a total of 465 twin pairs with a positive school history of reading problems. The basic and extended DeFries and Fulker (DF) multiple regression models for the analysis of selected twin data were employed to investigate the etiology of group deficits in reading and language skills, as well as to assess differential genetic etiology for the reading-related measures as a function of IQ. Data from 168 sibling pairs (drawn from the twins' families), including fraternal twin pairs and their siblings, as well as non-twin siblings of identical twins were subjected to single-marker analyses using the DF basic linkage model to examine evidence for linkage of a quantitative-trait locus (QTL) for reading and language deficits to the short arm of chromosome 6. Lastly, to investigate the possible differential influence of this QTL as a function of IQ, the sibling pair data were fitted to an extension of the DF basic linkage model. Results indicated that reading and language deficits are significantly heritable and that differential genetic influences as a function of IQ are evident for measures of word recognition and phonological decoding. Results obtained from linkage analyses confirmed the presence of a QTL on chromosome 6p that influences phonological and orthographic skills, as well as phoneme awareness measures, and suggest that this QTL may influence phoneme awareness differentially as a function of IQ: however, future analyses with considerably larger samples are needed to test the hypothesis of differential QTL influence more rigorously.

Geneticslinkage analysismultiple regressionreading disabilitysibling-pair studiestwin studiesquantitative-trait loci

Copyright information

© Plenum Publishing Corporation 2002