In genome-wide association studies (GWAS), researchers look for small variations in the sequences of human genes that are connected to some characteristic or condition. Scientists have now performed this type of study for stuttering, using data from the (now nonprofit) genomics company 23andMe Inc. The findings, which showed that stuttering can have a clear genetic basis, have been reported in Nature Genetics.
In this work, scientists analyzed data from 99,776 cases in which people had self-reported a stutter or stammer, and 1,023,243 people who did not self-report a stutter or stammer. The researchers found 57 unique locations in the human genome that are linked to stuttering, and determined that there is some overlap with genetic features of autism, musicality, and depression. There are 48 genes in these genomic loci that are linked to the risk of stuttering.
The findings were also used to create polygenic risk scores, which utilize genetic data to find the likelihood of some trait appearing in a person.
The work may help researchers understand the biological causes of stutter or stammer, and could help educate the general public and reduce the stigma attached to stuttering.
There are around 400 million people worldwide who are thought to stutter, which is defined as repetitions of syllables or words, prolongations of sound and breaks between words, explained Professor Jennifer (Piper) Below, PhD, director of the Vanderbilt Genetics Institute, among other appointments. It is more common in males.
"No one really understands why someone stutters; it has been a complete mystery. And that's true for most speech and language pathologies. They are profoundly understudied because they don't put people in the hospital, but they can have enormous consequences on people's quality of life," said Below. "We need to understand risk factors for speech and language traits so that we can identify kids early and get appropriate care for those that want it."
Stuttering can impact quality of life: children who stutter tend to experience more bullying and participate less in classrooms, for example. Employment opportunities, social well-being, and mental health can also be affected.
"There have been hundreds of years of misconceptions about what causes stuttering, from ideas about left-handedness to childhood trauma to overbearing mothers," Below said. "Rather than being caused by personal or familial failings or intelligence, our study shows that stuttering is influenced by our genes."
The gene most commonly linked to stuttering was VRK2. This gene has also been strongly linked to the self-reported ability to clap along with a beat. It has also been linked to language decline in Alzheimer's patients.
This work may indicate that there is a shared genetic architecture underlying speech, language, and musicality, Below suggested.
Sources: Vanderbilt University Medical Center, Nature Genetics