Dyslexia subtypes: genetics, behavior, and brain imaging.

This study was designed to identify inherited subtypes of specific dyslexia and to characterize these types by a variety of studies. A previous linkage study in large three-generation families resulted in a LOD score of 3.24 at a 13% recombination frequency between dyslexia and normal variations for the short arm of chromosome 15. The odds for linkage with chromosome 15 markers are better than 1,000 to 1. We estimate that 30% of an extended series of families show linkage to chromosome 15 polymorphisms. Other linkages remain to be identified. PET scanning is being used to examine measures of regional cerebral glucose metabolism during two types of reading by (adult) dyslexics and normal readers. MRI is also being used to examine pertinent brain structures. Behavioral tests are also in progress. The long-term goals of this study are to develop specific genetic and other diagnostic techniques that can be used to test children before beginning school and to develop sufficient understanding of the abnormal brain function of each subtype so that specific and effective remedial programs can be developed.