Speaking and squeaking may be two very different things, although a team of researchers at Washington University are hoping that stammering mice will squeak volumes about human speech impediments.
Why people stutter is something that is poorly understood, although studies have shown that many of those who suffer from this particular difficulty have a genetic mutation that affects their lysosomes. These are small, membrane-bound components of cells that play a role in breaking down waste materials, like a type of intracellular garbage disposal system.
Many people who stammer have been found to carry a mutated version of a gene called GNPTAB, which alters the efficiency of these lysosomes. Exactly how this causes stuttering is still something of a mystery, which is why researchers were keen to see if they could use mice to study the effects of this mutation in more detail.
Publishing their findings in the journal Current Biology, the study authors explain how they genetically engineered mice to carry a mutation on the GNPTAB gene. After doing so, they conducted a range of tests to determine whether or not this led to the rodents developing difficulties squeaking their minds.
Results showed that, compared to normal mice, the engineered mice tended to be much more repetitive in their vocalizations, using a higher percentage of syllables of a single type, with much longer gaps between squeaks. This pattern of “speech” was found to be identical to that of stuttering humans, to the point where a computer program designed to mathematically analyze speech patterns was unable to tell the difference between stammering mice and people.
Confident that the mutation therefore has the same effect on mice as it does on humans, the study authors subjected the mice to a range of other behavioral tests in order to try and learn more about how the condition works. Amazingly, after examining around 50 non-verbal attributes – such as balance, coordination, and memory – they found absolutely no different between stuttering mice and non-stuttering mice.
Commenting on this finding, lead researcher Timothy Holy described the speech impediment as “a very clean defect,” adding that “one of the things we find scientifically interesting about stuttering is that it is so precisely limited to speech.”
Having successfully shown that the same genetic mutation can cause the condition in both humans and mice, the researchers may now have a unique opportunity to investigate the wider biological implications of stuttering using their mouse model.
At present, they are no closer to understanding how deficient lysosomes produce the speech disorder, although, given the fact that rodents and humans use very different air-flow mechanisms when vocalizing, it is unlikely that the answer lies in the physical mechanisms by which sounds are produced.
Instead, the study authors speculate that the “primary deficit in stuttered speech [may be]the inability to initiate vocalization sequences.” More work will be needed in order to determine the accuracy of this assumption, although for now the significant finding is that when it comes to stuttering, it doesn’t make much difference if you are a man or a mouse.