ADHD and Reading Disability Share Genetic Root

Attention Deficit Hyperactivity Disorder (ADHD) and developmental reading disability (RD) are two childhood disorders that usually occur together, and a new study figured out the reason why.

The new research suggests that the two disorders have common genetic influences, and that this can also lead to a slow processing speed within the brain, which takes longer to understand all the information it receives.

The study's co-authors are Erik G. Willcutt, Rebecca S. Betjemann, Lauren M. McGrath, Nomita A. Chhabildas, Richard K. Olson, John C. DeFries and Bruce F. Pennington.

They looked at 457 pairs of twins from the Colorado Learning Disabilities Research Center (CLDRC) twin study, which focused on the causes of reading disabilities, ADHD, and other related disorders.

Dr Erik Willcutt and his colleagues compared groups of participants with RD and ADHD and without the disorders, AlphaGalileo reports.

They measured general cognitive ability, processing speed, reading and language skills, by using a variety of tests and then analyzed the results from pairs of twins within those groups to see the genetic causes of any correlations.

The researchers used identical twins sharing all their genes, and non-identical twins, sharing only half of their genes, and this allowed them to identify the genetic and environmental influences on the cognitive abilities of the subjects.

The results concluded that both RD and ADHD are very complex disorders, and they are influenced by many factors – ADHD was linked to a very low ability of controlling responses to stimuli, while RD were linked to several weaknesses in memory and language.

Nevertheless, they were both related to a slow processing speed, and thanks to the twin-analysis, the researchers found a genetic correlation between the two – an individual with one of the disorders was likely to have symptoms of the other as well.

The reason for this correlation remains unknown for now, so further research is necessary.

This study was reported in the latest special issue of Cortex, dedicated to “Developmental Dyslexia and Dysgraphia”.