Functional assays and drug screening for ion channels

Chai Ann Ng (Andy), PhD, Senior Staff Scientist, Victor Chang Cardiac Research Institute

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What is your first globally validated functional assay for ion channel variants and what does it do?

The first assay I established in 2022 is a functional assay that detects harmful ion channel variants in patients with long QT syndrome related to the dysfunction of cardiac potassium channels¹. It represents a global collaboration among researchers, clinical testing laboratories, clinical geneticists, genetic counsellors, and cardiologists².

In 2024, we collaborated with another lab in the US and successfully developed an assay for patients with Brugada Syndrome associated with cardiac sodium channel dysfunction³. Our functional assays have already helped patients with potassium and sodium channelopathies receive their diagnostic genetic test results^3-5.

Additionally, we have recently demonstrated that our assay can identify patients with high-risk long QT syndrome⁶. I aim to improve genetic diagnosis for patients with various channelopathies, including calcium channels encoded by the CACNA1C gene⁷.

Why is it important to reclassify Variants of Uncertain Significance (VUS), especially for ion channel variants and how could it impact our community

Pathogenic ion channel variants lead to a range of channelopathies, often manifesting as rare diseases. This is one reason many ion channel variants are clinically classified by testing laboratories as Variants of Uncertain Significance (VUS), due to insufficient evidence.

VUS is clinically unactionable, affecting family management and screening while causing unnecessary anxiety for patients, which ultimately undermines the purpose of undertaking genetic testing itself. It is vital to identify patients with harmful VUS and reclassify them as likely pathogenic to enable family screening that can detect and prevent adverse outcomes for asymptomatic family members.

What is your research project funded by the CVMM?

Ion channels play a crucial role in regulating the electrical activity and pumping function of the heart. Dysregulation of these ion channels can result in sudden cardiac arrest, including cases caused by ‘gain-of-function’ variants in the cardiac calcium ion channel. There is a significant unmet clinical need for treating gain-of-function calcium channel-related disorders.

My collaborative grant funded by The University of New South Wales’ Cardiac, Vascular, and Metabolic Medicine (CVMM) Theme aims to utilise the genetic variant that leads to Timothy Syndrome, a heart disease that can precipitate sudden cardiac arrest, to develop a genetic model aimed at identifying drugs that will benefit patients with Timothy Syndrome and may also be effective in treating ventricular arrhythmia.

What does performing a small-scale drug screening mean and how could it impact our community?

The funded project allows me to screen up to 10,000 drug-like molecules that could inhibit the gain-of-function activity underlying the disease mechanism of Timothy Syndrome. It acts as a proof-of-concept study to generate a pilot dataset for future grant applications. While it may not have an immediate impact on the calcium channelopathies community at present, we aim to identify and develop new molecules that may attract commercial interest in the future.

How does feeding back what you are up to through TSA help support PPIE?

Increasing awareness of my research through TSA for patients and the public will ideally encourage closer collaboration. Community-supported research can empower researchers to secure funding, which is crucial for rare diseases. Ultimately, I aim for my research to benefit society and aid patients with harmful ion channel variants in obtaining a diagnostic genetic test result.

References

1. Jiang C, Richardson E, Farr J, et al. A calibrated functional patch-clamp assay to enhance clinical variant interpretation in KCNH2-related long QT syndrome. Am J Hum Genet. Jul 7 2022;109(7):1199-1207. 

2. Thomson KL, Jiang C, Richardson E, et al. Clinical interpretation of KCNH2 variants using a robust PS3/BS3 functional patch-clamp assay. HGG Adv. Apr 11 2024;5(2):100270. 

3. Ma JG, O’Neill MJ, Richardson E, et al. Multisite Validation of a Functional Assay to Adjudicate SCN5A Brugada Syndrome-Associated Variants. Circ Genom Precis Med. Aug 2024;17(4):e004569. 

4. Ng C-A, O’Neill MJ, Padigepati SR, et al. Calibrated Functional Data Decreases Clinical Uncertainty for Tier 1 Monogenic Disease: Application to Long QT Syndrome. medRxiv. 2025:2025.02.05.25321617. 

5. Aljassar RW, Shen Q, Albash B, Vandenberg JI, Ebrahim MA, Ng CA. Integration of validated functional evidence to support the pathogenicity of KCNH2 variants. Genet Med Open. 2024;2:101868. 

6. O’Neill MJ, Ng CA, Aizawa T, et al. Multiplexed Assays of Variant Effect and Automated Patch Clamping Improve KCNH2-LQTS Variant Classification and Cardiac Event Risk Stratification. Circulation. Dec 3 2024;150(23):1869-1881. 

7. Tan C, Shen Q, Vandenberg J, Ng C. Establishing a Functional Genomics Assay to Assess Clinical Variants in CACNA1C-Related Disorders. Heart, Lung and Circulation. 2024;33:S117. 

Summary

Thanks to Daniel Haynes, PhD student funded by the Hodge Foundation, NMHII, Cardiff University.

In 2022, I developed a lab test that detects harmful gene changes in people with Long QT Syndrome, a heart condition caused by faulty potassium channels. We are now working to expand this to other conditions, including calcium channel disorders such as Timothy Syndrome.

My project, funded by the University of New South Wales’ Cardiac, Vascular, and Metabolic Medicine (CVMM) Theme, focuses on understanding and treating serious heart problems like those seen in Timothy Syndrome. As part of this work, we will screen up to 10,000 drug-like molecules to see if any can prevent the problems caused by faulty calcium channels.

Although this is early research, it could lead to future treatments and more funding for rare heart diseases. Sharing my work with the TSA keeps patients and families informed and involved, which is vital for raising awareness and supporting research.