The same genes may impair speech and later, reading

Researchers have found that several genes linked to reading disorder, also called dyslexia, are present in children with Speech Sound Disorder (SSD).

Older names for SSD, such as articulation disorder and phonological disorder, may be familiar to many parents, because about 16% of three-year-old children are affected by it. Many will learn to make themselves understood by the time they are six, leaving around 4% of children starting school with disordered speech.

Articulation is making sounds. Children who have articulation problems will substitute, leave out, or distort normal speech sounds. Of course, since we are born not knowing how to speak, some errors of articulation are a normal part of learning. For example, it is not unusual for three-year-olds to substitute the “f” sound for “th” in their speech; “I am firsty,” instead of thirsty. But these errors should fade slowly and be gone in the speech of a child over five.

Unexplained articulation problems

Dr. Shelley Smith, a genetics researcher and professor of paediatrics at the University of Nebraska Medical Center, started with over a hundred children with unexplained problems articulating the sounds of the English language, many of whom had not yet begun to learn to read. Dr. Smith and her team then pulled in 76 siblings of the affected children. After an array of tests to clarify exactly where in the complicated world of language disorders the children and their siblings stood, the researchers also asked for a cheek swab to look at the children’s genetics.

Some siblings of affected children had learned to speak in typical ways, making typical mistakes, but others were found to share their brother or sister’s SSD. By looking at the genes of the affected and unaffected children, researchers were able to confirm a close connection between several known reading disorder genes and the abnormal development of speech. Their findings were published in the Journal of Child Psychology and Psychiatry in October 2005.

Because of the wide variety of problems with communication that children may experience, it’s important to identify what SSD is not.

  • It’s not stuttering. Stuttering is a very common fluency disorder, which is different from an articulation disorder.
  • It’s not a physical problem with the parts of the mouth and throat that create speech, or the nerves that control them.
  • Problems with articulation can occur when there is damage or abnormal development of the speech motor centres of the brain, but this not SSD.
  • SSD is not a Specific Language Impairment, which would include deficits in comprehension, grammar, or both, as well as articulation problems. However, many children who have SSD or reading disorder also have a Specific Language Impairment.

Some researchers think SSD is caused by differences in the brain areas that process speech and speech sounds. The motor centres know how to move the lips, tongue, and vocal cords to make the required sounds, but the speech processing centres don’t know what the required sounds actually are. A genetic connection to reading disorder would support this theory, since most children who have trouble reading also have trouble perceiving, distinguishing, and manipulating the basic sounds of spoken language.

Reading disorder is diagnosed when children have unexpected trouble learning how to read. Between 3% and 15% of children have reading disorder. Evidence has been mounting for many years that reading disorder is caused by brain differences, and researchers can now point to both environmental and genetic risk factors.

Genes, articulation, and reading

There’s a consensus that children who experience trouble learning to speak are at increased risk of later having trouble learning to read. Researchers have recently been trying to track down a possible common underlying factor creating both problems.

Genetic testing for reading disorder risk genes is still a research tool. In the near future, both speech and reading disorders will continue to be diagnosed with careful psychological testing, not lab work. However, by increasing understanding of how speech and reading disorders are connected, researchers are putting early detection tools in the hands of parents, speech therapists, and doctors. So even if genetic tests for the disorders are never adopted, more children will get earlier intensive help with reading as a result of understanding how these disorders are related.

Dr. Cathy Barr, a senior scientist in the Brain & Behaviour Program at The Hospital for Sick Children and also at the Division of Cellular & Molecular Biology, Toronto Western Research Institute, stressed how important it is to notice when a child shows early warning signs of a language disorder. “Knowing your child is at risk, you can test reading and language skills early. Early vigilance and intervention can have a significant positive effect,” Dr. Barr said.

She added that “Down the road, our goal is to build up a model of how the brain develops an ability to read. This might show how single genes influence very complex and different traits like attentiveness and reading ability.” Dr. Smith’s research provides new and detailed evidence that some of those same genes may also bring on the timely development of intelligible speech.

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