Mice with squeak impediments have been created by scientists to help them study human speech disorders.
Mouse pups with a special genetic mutation squeaked in high-pitched sounds with longer pauses and a repetitive staccato pattern, similar to the utterances made by people who stammer.
Scientists recorded the noises made by the mice until they were eight days old, with each recording session lasting 3.5 minutes.
Studying the mice, scientists found “abnormalities that mimic some features of human stuttering,” said Dr Terra Barnes, a scientist at Washington University School Medicine in St Louis, whose research is published in the journal of Current Biology.
The mutated mice produced nearly a third fewer sounds and emitted more singular syllables than mice without the mutated gene. The pauses proved similar to the hesitations that fragment the flow of speech in human stutterers, while the repetition reflected human stammering.
Another quality of stuttering is that, whatever its cause, it only affects speech. After being put through a range of tests measuring factors including balance, strength, co-ordination, movement, leaning, memory and sociability, the mice were also found to be healthy and normal in every other respect.
"One of the things we find scientifically interesting about stuttering is that it is so precisely limited to speech, It’s a very clean defect in an incredibly complex task,” said Dr Tim Holy, associate professor of neuroscience at Washington University.
Nervousness, stress and even bad parenting have previously been labelled as causes of stammering. However, the principal cause of the impediment is now understood to be biological, with anxiety exacerbating the disorder.
The modified mice had the same mutant version of a gene linked to human stammering – the defective gene Gnptab that famously plagued King George VI.
In 2010, researchers found mutations in the gene Gnptab appeared to cause stuttering in some people. The discovery was surprising as the Gnptab gene’s primary role is to help cells dispose of unwanted molecules.
“It’s kind of crazy that this gene that’s involved in digesting the garbage in your cells is somehow linked to something so specific as stuttering,” said Dr Holy. “It could be that the protein has many functions and this mutation affects only one of them.”
The findings suggest mice could lead to a new understanding of stuttering and ultimately to treatments that could help millions of people around the world who stutter.
Dr Holy said: “Speech is obviously a unique human capacity, but the patterns of speech are built out of a lot of building blocks that are much simpler.
“You have to be able to control the timing of your breath and the fine muscles in your tongue and mouth. You have to be able to initiate movement. Those kind of things may be shared all the way from mice to people.”
Dr Dennis Drayna, a geneticist with the National Institute on Deafness and Other Communication Disorders, said: “While it's surprising that the disorder can, to some degree, be recreated in a mouse, having an experimentally tractable animal model for some aspects of this disorder presents many exciting, new opportunities to move research in this area forward."
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