Key Points

Stuttering -- characterised by syllable and word repetitions, sound prolongations, and breaks between words -- is the most common fluency disorder, with more than 400 million people affected worldwide. And yet, the causes of this common speech disorder are unclear.

In the paper, published in the journal Nature Genetics, the researchers identified 48 genes, and 57 distinct genomic loci associated with the speech disorder, based on genetic data of more than 1 million individuals.

The findings may lead to earlier identification or therapeutic advances in stuttering and help replace outdated views of stuttering often held by the general public that contribute to stigma, said the researchers.

"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 Jennifer (Piper) Below, Professor of Medicine at Vanderbilt University Medical Center.

"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," she said.

Young people who stutter report increased bullying, decreased classroom participation, and a more negative educational experience.

Stuttering can also negatively impact employment opportunities and perceived job performance, and mental and social well-being, Below noted.

"Rather than being caused by personal or familial failings or intelligence, our study shows that stuttering is influenced by our genes," Below said.

Developmental stuttering onset typically occurs in children between the ages of 2 and 5, and about 80 per cent of children will spontaneously recover, with or without speech therapy.

At its onset, stuttering affects both males and females, but it is more common in adolescent and adult males (4:1 ratio of males to females) because of differences in the rate of spontaneous recovery by sex.

To decode the difference, the researchers also conducted studies on eight sex- and ancestry-specific groups, followed by meta-analyses that combined the findings.

They identified 57 distinct genomic loci, which mapped to 48 genes, associated with stuttering risk. The genetic signatures differed between males and females, which could relate to persistent stuttering versus recovered stuttering, Below said.

- IANS