People affected by dyslexia often go undiagnosed until they're well into high school — living years without intervention and with stunted academic performance. The inability to recognize the order of words and letters within words is the hallmark of dyslexia, and prevents people from being able to read and write properly. Researchers have long suspected a genetic basis for dyslexia and that similar genetic issues may be responsible for impairments in language development and understanding. Dyslexia can affect anywhere from five to ten percent of the population, although no solid studies have been done to determine the prevalence.
Scientists from the Yale School of Medicine have published results from their analysis of over 10,000 students born between 1991 and 1992. All of the students' data was collected from the Avon Longitudinal Study of Parents and Children (ALSPAC) conducted by researchers at the University of Bristol in the United Kingdom. By comparing the incidence of language impairment and dyslexia to genetic variants of the DCDC2 gene, the researchers found that different mutations on different parts of the same gene were responsible for two different conditions.
Previously the same research group, headed by Jeffrey R. Gruen, M.D., professor of pediatrics, genetics, and investigative medicine at Yale, found that the DCDC2 gene and a related gene called ANKK1 were involved in the processing of language, and that DCDC2 specifically was linked to dyslexia. Both DCDC2 and ANKK1 are related to the signal transduction of dopamine, a neurotransmitter molecule.
The current study found that genetic differences in a regulatory element called READ1 (regulatory element associated with dyslexia1), which was contained within the DCDC2 gene, were directly linked to both dyslexia and language impairment, separately. Regulatory elements control when and where a gene will be expressed and made into a protein. Deregulation of gene production invariably has physiological effects that can impact both health and development.
The variants of READ1 interact with another gene that has been associated with dyslexia risk called KIAA0319. "When you have risk variants in both READ1 and KIAA0319, it can have a multiplier effect on measures of reading, language, and IQ," said Gruen. "People who have these variants have a substantially increased likelihood of developing dyslexia or language impairment."
It is known that fetal exposure to nicotine can predispose children to language and language processing problems. But the new research offers a definitive genetic cause that can be tested for in young children, even before they begin formal education. The ability to test for language issues or dyslexia even before children start to develop language and reading skills can result in earlier interventions.
"These findings are helping us to identify the pathways for fluent reading, the components of those pathways; and how they interact," said Gruen in a press release. "We now hope to be able to offer a pre-symptomatic diagnostic panel, so we can identify children at risk before they get into trouble at school. Almost three-quarters of these children will be reading at grade level if they get early intervention, and we know that intervention can have a positive lasting effect."
Source: Powers N, Eicher J, Butter F, et al. Alleles of a Polymorphic ETV6 Binding Site in DCDC2 Confer Risk of Reading and Language Impairment. The American Journal of Human Genetics. 2013.