A team of researchers from the University of California, San Francisco claims to have identified in a group of individuals with attention deficit hyperactivity disorder four chromosomal regions that contain genes that may influence reading ability.
The team performed a systematic genome-wide investigation of reading ability in a sample of 233 siblings pairs diagnosed with ADHD. The researchers measured reading ability by three types of tests: a spelling task, a reading recognition task, and a reading comprehension task. Because performance from all three was “highly correlated,” the researchers used in the analysis not only the individual test scores but also a “reading factor” representing performance on the tests.
The researchers used a set of molecular markers covering the human genome at about a 10cM density 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,” the team explained in a brief statement.
The researchers identified regions on chromosomes 2p, 10q, 16p, and 17q that “suggest evidence for linkage.” Three of these areas — 10q, 16p, 17q — overlapped regions suggested by earlier studies of ADHD. Meantime, one region, 2p, overlapped earlier research into 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,” the team wrote in the statement. “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.”
The study, led by UCLA researcher Sandra Loo, appears in the December issue of Molecular Psychiatry.
ADHD and RD “are common disorders” of childhood that often co-occur. It is estimated that between 20 percent and 25 percent of children and adolescents with ADHD have a reading disability, though the causes of this association are unknown.