title: Evidence for a susceptibility locus on chromosome 6q influencing phonological coding dyslexia.
abstract: A linkage study of 96 dyslexia families containing at least two affected siblings (totaling 877 individuals) has found evidence for a dyslexia susceptibility gene on chromosome 6q11.2-q12 (assigned the name DYX4). Using a qualitative phonological coding dyslexia (PCD) phenotype (affected, unaffected, or uncertain diagnoses), two-point parametric analyses found highly suggestive evidence for linkage between PCD and markers D6S254, D6S965, D6S280, and D6S251 (LOD(max) scores = 2.4 to 2.8) across an 11 cM region. Multipoint parametric analysis supported linkage of PCD to this region (peak HLOD = 1.6), as did multipoint nonparametric linkage analysis (P = 0.012). Quantitative trait linkage analyses of four reading measures (phonological awareness, phonological coding, spelling, and rapid automatized naming speed) also provided evidence for a dyslexia susceptibility locus on chromosome 6q. Using a variance-component approach, analysis of phonological coding and spelling measures resulted in peak LOD scores at D6S965 of 2.1 and 3.3, respectively, under 2 degrees of freedom. Furthermore, multipoint nonparametric quantitative trait sibpair analyses suggested linkage between the 6q region and phonological awareness, phonological coding, and spelling (P = 0.018, 0.017, 0.0005, respectively, for unweighted sibpairs < 18 years of age). Although conventional significance thresholds were not reached in the linkage analyses, the chromosome 6q11.2-q12 region clearly warrants investigation in other dyslexia family samples to attempt replication and confirmation of a dyslexia susceptibility gene in this region.
authors.affiliation: Department of Medical Genetics, University of Calgary, Calgary, Alberta, Canada. llfield@interchange.ubc.ca
authors.forename: T L
authors.initials: TL
authors.lastname: Petryshen
authors.forename: B J
authors.initials: BJ
authors.lastname: Kaplan
authors.forename: M
authors.initials: M
authors.lastname: Fu Liu
authors.forename: N S
authors.initials: NS
authors.lastname: de French
authors.forename: R
authors.initials: R
authors.lastname: Tobias
authors.forename: M L
authors.initials: ML
authors.lastname: Hughes
authors.forename: L L
authors.initials: LL
authors.lastname: Field
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002896:Chromosomes, Human, Pair 6 / Q000235:genetics*; D004410:Dyslexia / Q000235:genetics*; D005192:Family Health; D005260:Female; D008040:Genetic Linkage; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006239:Haplotypes; D006801:Humans; D015810:Linkage Disequilibrium; D008126:Lod Score; D008297:Male; D018895:Microsatellite Repeats; D009679:Nuclear Family; D010641:Phenotype