Dyslexia and DCDC2: normal variation in reading and spelling is associated with DCDC2 polymorphisms in an Australian population sample

The 6p21-p22 chromosomal region has been identified as a developmental dyslexia locus both in linkage and association studies, the latter generating evidence for the doublecortin domain containing 2 (DCDC2) as a candidate gene at this locus (and also for KIAA0319). Here, we report an association between DCDC2 and reading and spelling ability in 522 families of adolescent twins unselected for reading impairment. Family-based association was conducted on 21 single nucleotide polymorphisms (SNPs) in DCDC2 using quantitative measures of lexical processing (irregular-word reading), phonological decoding (non-word reading) and spelling-based measures of dyslexia derived from the Components of Reading Examination test. Significant support for association was found for rs1419228 with regular-word reading and spelling (P=0.002) as well as irregular-word reading (P=0.004), whereas rs1091047 was significantly associated (P=0.003) with irregular-word reading (a measure of lexical storage). Four additional SNPs (rs9467075, rs9467076, rs7765678 and rs6922023) were nominally associated with reading and spelling. This study provides support for DCDC2 as a risk gene for reading disorder, and suggests that this risk factor acts on normally varying reading skill in the general population.