Dyslexia is a common and genetically complex trait that manifests primarily as a reading disability independent of general intelligence and educational opportunity. Strong evidence for a dyslexia susceptibility locus on chromosome 1p34-p36 (near marker D1S199) was recently reported, and an earlier study found suggestive evidence for linkage to the same region. We tested for the presence of a dyslexia gene in this region in a sample of 100 Canadian families using both qualitative and quantitative definitions of the phenotype. Using a qualitative definition of dyslexia (affected, unaffected, or uncertain), the largest multipoint Genehunter Maximum LOD-Score (MLS) in 100 core nuclear families was 3.65 at D1S507, distal to D1S199. Quantitative trait locus (QTL) linkage analysis was performed for four measures of dyslexia (phonological awareness, phonological coding, spelling, and rapid automatized naming speed) employing the variance components approach implemented in Genehunter. Using a model with QTL additive and dominance variance and polygenic additive variance, the multipoint LOD scores maximized proximal to D1S199 (between D1S552 and D1S1622), with peaks of 4.01 for spelling and 1.65 for phonological coding (corresponding LOD scores under 1 degree of freedom were 3.30 and 1.13, respectively). In conclusion, our study confirms and strengthens recent findings of a dyslexia susceptibility gene on chromosome 1p34-p36 (now designated DYX8).
Copyright 2003 Wiley-Liss, Inc.