(RxWiki News) Attention Deficit Hyperactivity Disorder (ADHD) and developmental reading disability (RD) frequently occur together in children, though the reason for this correlation remains unknown.
A new study in the latest issue of Cortex suggests the disorders have common genetic influences. This may lead to slow-processing speed in the brain, which takes longer to process the information it receives.
Researchers looked at 457 pairs of twins from the Colorado Learning Disabilities Research Center (CLDRC) twin study, an ongoing effort that analyzes the causes of reading disabilities, ADHD, and related disorders. Using numerous tests to measure general cognitive ability, processing speed, reading and language skills, the researchers analyzed results from pairs of twins (in groups with and without RD and ADHD) to determine the genetic causes of any correlations between the two groups.
Dr. Erik Willcutt and colleagues discovered RD and ADHD are complex disorders, influenced by many factors. On its own, ADHD was associated with reduced ability to inhibit responses to stimuli. Reading disabilities on the other hand were associated with various weaknesses in language and memory. Both disorders were linked to slow processing speed, and participants with one of the disorders were more likely to show symptoms of the other.
Attention Deficit Disorder (ADD) is the most commonly diagnosed behavioral childhood disorder. It affects an estimated 3 percent to 5 percent of school-aged children.