Varieties of Developmental Reading Disorder: Genetic and Environmental Influences

Anne Castles*, Helen Datta, Javier Gayan, Richard K. Olson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

169 Citations (Scopus)


There is widespread support for the notion that subgroups of dyslexies can be identified who differ in their reading profiles: Developmental phonological dyslexia is characterized by poor nonword reading, while developmental surface dyslexia is distinguished by a particular difficulty in reading irregular words. However, there is much less agreement about how these subtypes, and particularly the surface dyslexic pattern, are to be accounted for within theoretical models of the reading system. To assist in addressing this issue, the heritability of reading deficits in dyslexic subtypes was examined using a twin sample. Subjects' scores on (a) an exception word reading task and (b) a nonword reading task were used to create a subtype dimension, and surface and phonological dyslexic subgroups were selected from the ends of this distribution. Reading deficits were found to be significantly heritable in both subgroups. However, the genetic contribution to the group reading deficit was much greater in the phonological dyslexies than in the surface dyslexies. The finding of differential genetic etiology across subtypes suggests that there is at least partial independence in the development of the cognitive processes involved in reading exception words and nonwords. Also, the results support accounts of surface dyslexia which emphasize a strong environmental contribution.

Original languageEnglish
Pages (from-to)73-94
Number of pages22
JournalJournal of Experimental Child Psychology
Issue number2
Publication statusPublished - Feb 1999
Externally publishedYes


  • Behavioral genetics
  • Dyslexia
  • Genetic influences
  • Orthographic deficits
  • Phonological deficits
  • Reading disorders
  • Subtypes of dyslexia


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