Newly identified mutations in SCA19/22 and their dysfunctions

Written by Sophia Leung Edited by Dr. Marija Cvetanovic

While the mutant proteins in SCA19/22 lose part of their innate functions and properties, they also disrupt the key functions of the normal healthy protein.

The underlying mechanism of the hereditary property of SCA19/22 is elusive. In this study, the researchers investigated the molecular properties of four different mutations found in patients with SCA19/22. They looked at how these mutant proteins affect the normal protein if they are both present in the cell. They found that the mutant proteins are not only non-functional (do not work properly), but that in their presence, the normal protein’s function is also diminished. Furthermore, while the production and proper localization of these mutant proteins are found to be defective, they also bring the same decline to the normal protein. This adds to their disease-causing properties. This study is significant in that it offers a molecular investigation into mutant proteins associated with SCA19/22 that was previously lacking. It also provides evidence that may explain the hereditary property of the disease.

A number of mutations in the gene KCND3 has been associated with SCA19/22. The gene makes the voltage‐gated potassium ion (K+) channel subunit KV4.3. In general terms, the gene makes a protein that functions to allow potassium ions to pass through the membrane of nerve cells. Similar to how a flute has many holes to allow air to pass through when played to make a specific note, a nerve cell has different kinds of channels to allow ions to pass through their membrane to orchestrate normal functioning. One could imagine the disruption to any channels, a partial obstruction or a total blockage, could perturb the overall output of the cell.

flute resting on a music stand
Similar to how a flute has many holes to allow air to pass through when played to make a specific note, a nerve cell has different kinds of channels to allow ions to pass through to orchestrate normal functioning. (Photo by Rajesh Kavasseri / Unsplash)

In this study, the researchers found that the normal KV4.3 channel protein detectably allows potassium ions to pass through. But little to no ions can pass through the SCA19/22 mutant KV4.3 channels. Even under the assistance of a “helper” protein, which normally enhances the function of this channel, only one of the mutant channel proteins shows improvement. This indicates that the SCA19/22 causing mutations result in a reduced function of mutated KV4.3 channels.

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