In a systematic genome-wide investigation of reading ability in a sample of 233 siblings diagnosed with ADHD, four chromosomal regions emerged as potential locations for genes underlying reading ability. Reading ability was measured by three types of reading tests including a spelling task, a reading recognition task, and a reading comprehension task. Because performance on all three measures was highly correlated, a reading factor representing performance on all three was used in the analysis, as well as the individual test scores. A dense set of highly informative molecular markers covering the human genome at about a 10cM density was used to investigate linkage. Linkage was determined based on increased sharing of molecular markers across the 233 sibling pairs against that expected for siblings due to their degree of genetic relationship.
Four regions found on chromosomes 2p, 10q, 16p, and 17q, showed suggestive evidence for linkage. Three of the locations (10q, 16p, 17q) overlapped regions suggested from previous investigations of ADHD and one region (2p) overlapped that suggested from previous studies of RD. These findings support the idea that common genes may underlie ADHD and RD but also that reading ability and RD have genetic underpinnings that differ from those underlying ADHD as well. However, since each region that overlaps ADHD and reading ability harbors hundreds of genes, further work is required to identify specific genetic variants underlying ADHD and RD and to determine if they are actually the same or different.