What is it? What will it tell us?
How will it benefit people who stutter?
by Dennis Drayna, PhD
National Institute on Deafness and
Other Communication Disorders
National Institutes of Health
Research advances in genetics are in the news almost every day. Many of these news reports tell of the discovery of a gene that causes a disease or other medical problem. While these reports are often exciting and provocative, it is often not easy to understand exactly what has been discovered and how that discovery will help the people with that disorder. There are a number of studies on the genetics of stuttering now in progress. Findings from these studies are beginning to appear, and there is much hope that more discoveries, telling us more important information about stuttering, will soon be made. What exactly are these studies, and what do scientists hope to learn from them?
Several of the current genetic studies on stuttering, including our NIH Family Research Project on Stuttering, are technically known as linkage studies. In linkage studies, scientists attempt to find genetic markers that are co-inherited with stuttering in families. This co-inheritance in families is known as linkage. When a marker or markers show co-inheritance with stuttering, scientists know that these markers lie very close to the gene or genes that help cause stuttering in those families. Since scientists already know the location of each marker they test, discovering linkage to a marker tells them the location of the gene(s) involved. If scientists can find the location of these genes, they can learn a great deal about the contribution of each one of those genes to stuttering. In addition, they can use the information on where the genes are located to find, isolate, and study these genes.
What are these genetic markers? Anything that shows inherited differences in people is a genetic marker. A good example is your blood type. A person's blood type can be type A, type B, or type O, and each person inherits their blood type from their parents. The gene which specifies blood type resides on chromosome number 9. One of the first examples of linkage ever demonstrated in humans was co-inheritance of ABO blood type with a rare and unusual disease called nail-patella syndrome, in which people have abnormal fingernails and kneecaps. Knowing that the gene causing nail-patella syndrome is linked to the ABO blood type gene told scientists that the nail-patella syndrome gene is on chromosome number 9 as well. This information on where this gene is located allowed scientists to find this gene and to see how it was different in people with nail-patella syndrome. This discovery revealed new information on how fingernails and kneecaps develop, and how these two parts of the body are actually related to each other. The goal of linkage studies on stuttering are exactly the same.
Scientists hope to find the genes that can cause stuttering, to see what these genes do, both in normally fluent people and in those who stutter. How will this help people who stutter? First, despite decades of effort by dedicated researchers, no underlying cause of stuttering has been found. While many stuttering therapy methods have proven to be helpful, understanding the underlying causes of stuttering will be a tremendous aid in designing new and better therapies. Even before this point, however, having good genetic markers for stuttering could help with stuttering diagnosis, identifying those that stutter because of genetic factors. These could help identify individuals at risk in families, and help get early intervention started in those who need it most. It's an exciting time in stuttering research. We have good reason to hope for better understanding of this age-old problem within the coming few years.