Linkage studies suggest a possible locus for developmental dyslexia on chromosome 1p

Eight extended dyslexic families with at least four affected individuals we re genotyped with twelve genetic markers spanning the Rh (rhesus factor) lo cus. Eleven of these markers were located on the short arm and the other wa s on the long arm of chromosome 1. Five theoretically derived phenotypes we re used in the linkage analyses: 1) phonemic awareness; 2) phonological dec oding; 3) rapid automatized naming; 4) single word reading; and 5) vocabula ry. In addition, a lifetime diagnosis of dyslexia was used as a phenotype. Both parametric and non-parametric genetic analyses were completed. The res ults supported the importance of a putative locus on 1p. In addition, two-l ocus analyses assuming the interaction between a 1p locus and a 6p locus, p reviously shown to be of interest for dyslexia, were conducted. As a result , the nonparametric linkage (NPL) scores for rapid automatized naming and p honological decoding were significantly increased. In particular, the NPL s cores for rapid automatized naming exceeded 5.0 for certain markers. These results provide strong evidence for separate but jointly acting contributio ns of the 1p and 6p loci to the reading impairments associated with rapid n aming and suggestive evidence for a similar mechanism involving phonologica l decoding. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 105:120-129, 2001. (C) 2001 Wiley-Liss, Inc.