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Dyslexia: A Disease Without a Country

It has long been noted that the prevalence of dyslexia varies with the ratio of sounds to written letters in the native language. Thus, in Italy, where the language contains 25 sounds to 33 letter combinations, the prevalence of dyslexia is low, but in English-speaking and French-speaking countries, where there are at least 40 sounds to 1120 letter combinations, the prevalence of dyslexia is relatively high. To determine whether dyslexic individuals have similar brain activity regardless of their native languages, researchers administered IQ and specific reading tasks to 54 Italian, French, and British dyslexics (age range, 21 to 27) and to 76 matched controls as they underwent labeled-water PET scans.

Previously diagnosed dyslexics with college-level educations were selected from the U.K. and France; because of difficulty in locating college-educated dyslexics in Italy (likely due to the overall low prevalence), Italian dyslexics were chosen after more complicated screenings. Dyslexics from all 3 countries scored worse than controls on all reading tasks. Although Italian-speaking dyslexics did score lower than Italian controls, they were less impaired on reading tasks than English- or French-speaking dyslexics. Dyslexics from all 3 countries had similar PET scans with reduced activity in the left middle, inferior, and superior temporal gyri and the middle occipital gyrus, compared with findings for controls.

Comment: This impressive study establishes that the neurologic mechanisms of dyslexia are similar regardless of native language. The brain regions involved correspond to areas of the brain concerned with language processing and are consistent with postmortem findings of ectopic areas in the cortex and dyslamination of cortical layers of dyslexic individuals.

— B Geller

Published in Journal Watch Psychiatry April 10, 2001

Citation(s):

Paulesu E et al. Dyslexia: Cultural diversity and biological unity. Science 2001 Mar 16 291 2165-2167.

• Original article (Subscription may be required)
• Medline abstract (Free)

Helmuth L. Commentary: Dyslexia: Same brains, different languages. Science 2001 Mar 16 291 2064-2064.

• Original article (Subscription may be required)
• Medline abstract (Free)

Reader Remarks:

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• Dyslexia
  JJ Curran, Co.Down, 9 Apr 2010 10:41 AM EST
  How do we know that the dyslexics in all three countries were not a result of poor teaching rather than... [more]
• A response from JW Psychiatry Associate Editor Barbara Geller
  Barbara Geller, MD, Emeritus Professor of Psychiatry, Department of Psychiatry, Washington University in St. Louis, 9 Apr 2010 2:41 PM EST
  The question of the effect of teaching on dyslexia is important. For this reason, the authors of this study used... [more]
• Dyslexia
  JJ Curran, Co. Down, 10 Apr 2010 4:02 PM EST
  Thank you Professor Geller for your response. A friend that I have discussed this subject with feels that it is... [more]