Since 1997, it has been known that mutations to the KCNQ4 K+ channel, a potassium ion pathway only found in three places: 1) on sound-detecting hair cells in the inner ear that leads from the external environment to neurons, 2) a part of the brain stem involved in hearing, and 3) neurons in the skin that help us to sense touch on mutations, lead to progressive deafness. Now a new study on mutations in this same pathway suggests that they also cause heightened sensitivity in skin. The researchers found that in both mice and humans, they disrupt the channel’s buffering ability, which would normally prevent neurons from becoming over-stimulated as stimuli is passed from the channel to the neurons. As this ability to buffer decreases in the inner ear, the hair cells slowly die, which leads to deafness.
[caption id="attachment_3237" align="aligncenter" width="519" caption="The KCNQ4 gene is located on base pair 41,249,683 to base pair 41,306,123 on the short (p) arm of chromosome 1 at position 34, as shown here."][/caption]
Additionally, the team discovered that in mice and human families with this gene mutation, the channel only appeared in neurons in skin that were sensitive to low level vibrations, and that humans with the mutation are better able to discern the subtle differences between various soft materials because of this. They also found that this heightened sensitivity to these types of touch was actually in existence before they went blind, meaning that this sensitivity was not a subsequent adaptation made by the body. Finally, they noted that this particular gene mutation in the KCNQ4 channel is one of many gene mutations that can cause deafness, leading them to conclude that not all those who develop progressive deafness will necessarily develop this type of sensitivity to touch.
The idea that certain traits can be inherited simultaneously (in this case, progressive deafness and increased skin sensitivity) is not a new one – a very common example is sex-linked disorders. However, genetic mutations such as this one are still very mysterious in nature simply due to the fact that there are many similar channels, such as the KCNQ1 channel, that have yet to be studied extensively.
The abstract of the original research article can be found here.