Understanding the complex etiologies of developmental disorders: Behavioral and molecular genetic approaches

Erik G. Willcutt, Bruce F. Pennington, Laramie Duncan, Shelley D. Smith, Janice M. Keenan, Sally Wadsworth, John C. Defries, Richard K. Olson

Research output: Contribution to journalArticlepeer-review

95 Scopus citations


Objective: This article has 2 primary goals. First, a brief tutorial on behavioral and molecular genetic methods is provided for readers without extensive training in these areas. To illustrate the application of these approaches to developmental disorders, etiologically informative studies of reading disability (RD), math disability (MD), and attention-deficit hyperactivity disorder (ADHD) are then reviewed. Implications of the results for these specific disorders and for developmental disabilities as a whole are discussed, and novel directions for future research are highlighted. Method: Previous family and twin studies of RD, MD, and ADHD are reviewed systematically, and the extensive molecular genetic literatures on each disorder are summarized. To illustrate 4 novel extensions of these etiologically informative approaches, new data are presented from the Colorado Learning Disabilities Research Center, an ongoing twin study of the etiology of RD, ADHD, MD, and related disorders. Conclusions: RD, MD, and ADHD are familial and heritable, and co-occur more frequently than expected by chance. Molecular genetic studies suggest that all 3 disorders have complex etiologies, with multiple genetic and environmental risk factors each contributing to overall risk for each disorder. Neuropsychological analyses indicate that the 3 disorders are each associated with multiple neuropsychological weaknesses, and initial evidence suggests that comorbidity between the 3 disorders is due to common genetic risk factors that lead to slow processing speed.

Original languageEnglish (US)
Pages (from-to)533-544
Number of pages12
JournalJournal of Developmental and Behavioral Pediatrics
Issue number7
StatePublished - Sep 2010


  • ADHD
  • genetics
  • math
  • reading
  • twins

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Developmental and Educational Psychology
  • Psychiatry and Mental health


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