Detecting differences in calcium influx

Richard Dolder, Graduate Student in Human Genetics, Glazer Laboratory, Vanderbilt University Medical Center

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Variants in the CACNA1C gene can cause a change in the function of the calcium
channel Ca_V 1.2. Ca_V 1.2 is responsible for facilitating the flow of calcium ions from outside the cell to inside the cell. This regulated calcium flow is crucial to the activity of both cardiomyocytes in the heart and neurons in the brain. Therefore, variants in CACNA1C that alter the channel’s regular function can cause multisystem disorders affecting the heart and brain.

The most common variant associated with Timothy syndrome is G406R, where the 406th amino acid is altered from glycine to arginine. This variant is well-studied and known to be pathogenic, allowing clinicians to quickly assess its effects and decide on subsequent actions when it appears in a patient. Several other well-studied variants are already known to be pathogenic or benign. Unfortunately, for most CACNA1C variants, very little information is available regarding their effects, making clinical decisions challenging. These understudied variants are called variants of uncertain significance (VUS).

The goal of the Glazer Lab is to assist in the reclassification of VUS into more clinically actionable categories. We have helped develop a new technique, Deep Mutational Scanning, to test the effects of thousands of variants in a single experiment. The Glazer Lab plans to assess the impact of all single amino acid variants in CACNA1C on its primary function, calcium influx. Preliminary data has already shown promising results for a fluorescent method to detect differences in calcium influx between different variants. If this project is successful, any time new patients with CACNA1C variants are found, there will be some data available on that variant’s effect on channel function.

While there is considerable nuance in how CACNA1C functions, and this method will not measure all the complicated functions of the protein, this research aims to provide some data on a key role of CACNA1C function for all possible variants. This will aid in both the diagnosis of Timothy Syndrome and CACNA1C-related disorders and enhance our overall understanding of how this complex channel operates.