A recent study from UHN's Krembil Brain Institute has identified genetic variants that are linked to reading disability.
Reading disability, also known as developmental dyslexia, is a complex neurodevelopmental disorder that affects five per cent to seven per cent of individuals in North America.
Individuals with the disorder have difficulty with word reading and spelling, despite typical overall intelligence. Children with reading disability often have co-existing conditions, such as attention-deficit/hyperactivity disorder (ADHD) and other language-based disorders.
"Although the molecular mechanisms that underlie reading disability are not fully understood, studies have identified genes associated with the condition," says Krembil Senior Scientist
Dr. Cathy Barr, who is also a professor in the Departments of Psychiatry and Physiology at the University of Toronto, and a Senior Scientist at The Hospital for Sick Children.
"Several of these genes play important roles in different aspects brain development, such as neuronal migration and axon guidance, and have been associated with autism."
Recent studies have analyzed millions of common genetic variants to uncover those associated with reading disability. However, the numbers of individuals included in these studies have often been too small for the findings to be conclusive.
To address this limitation, Dr. Barr's team used a more powerful approach. They conducted a genome-wide association study that focused on DNA sequences that have been previously linked to brain development or autism susceptibility.
"Identifying genetic variants can be difficult because the human genome contains more than three billion nucleotides that code for over 20,000 genes," explains Dr. Barr. "By zeroing in on key locations within the genome that were identified in previous studies, we were able to focus our efforts."
The team analyzed a sample of 624 individuals from Toronto as well as a large genomic data set that included more than 27,000 individuals from around the world (GenLang Consortium).
Using their Toronto sample, the team found that certain genes associated with autism were also linked to reading disability. In the larger sample, the team uncovered disease-relevant variants in genes that had not been implicated in reading disability in previous studies, as well as genes that had.
"Our findings in the Toronto sample suggest that genes that contribute to autism and brain development may play a role in the genetic basis of reading disability, which makes sense as there is often overlap between neurodevelopmental disorders," says Dr. Kaitlyn Price, a former PhD student in Dr. Barr's lab and the first author of the study.
"The next challenge is to define the molecular mechanisms that underlie how these DNA variations may alter the function of brain cells and cause reading disability."
This work was supported by the Canadian Institutes of Health Research, The Hospital for Sick Children, the Max Planck Society and UHN Foundation.
