Abstract 4147136: Functional Consequences and Phenotypic Manifestations of <i>KCNJ2</i> Variants in Andersen-Tawil Syndrome

Introduction: Andersen-Tawil Syndrome (ATS) is a rare genetic disorder characterized by periodic paralysis, skeletal abnormalities, and elongated QTc. ATS is caused by mutations in KCNJ2 , which encodes the inwardly rectifying Kir2.1 channel that constitutes IK 1 in the heart. Out of 2.3 million subjects in our EHR, only 3 had an ATS diagnosis, confirmed by clinical genetic testing. Due to the low prevalence and variable expressivity, diagnosing ATS is challenging. Hypothesis: ATS is often misdiagnosed and protein truncating variants (PTV) in KCNJ2 are not sufficient to cause disease. Methods: For 173,589 patients with exome sequencing in the EHR we identified all KCNJ2 variants with allele frequency &lt;0.01 and performed gene burden testing using REGENIE. We performed chart reviews and functional testing on all subjects with PTVs and any missense variant with at least one carrier with LQTS or ATS. Variants were tested by whole cell patch clamp, western blot, and immunofluorescence for function, expression and localization, respectively. Dominant negative effect was assessed by co-expressing the wild-type channels. Results: Gene burden analysis revealed cardiac arrhythmias as the only phenotype significantly associated with alpha-missense predicted pathogenic KCNJ2 variants. We found 11 carriers of 4 PTVs (R40Ter, E118Ter, E241fs, L368fs). We also found 5 carriers of 4 missense variants V4E, T75M, R218W, and R312H, which had at least one diagnosis of LQTS or ATS. In whole-cell patch clamp, PTVs did not produce functional channels or affect the function of co-expressed wild-type channels. None of the PTV carriers had ATS. Patients with LQTS diagnoses and PTV variants often had secondary underrated conditions, which can result in elongated QT intervals. V4E showed no functional deficits or dominant effects, and the carrier lacked ATS phenotype with a LQTS diagnosis due to an acute electrolyte imbalance. Variants T75M, R218W, and R312H produced small currents and exhibited dominant negative effects when co-expressed with WT channels. T75M reduced current size and altered channel rectification, and R218W and R312H reduced PIP 2 interactions. Four carriers of these missense variants, including a mother-son pair with the T75M variant, manifested various ATS-related phenotypes. Conclusions: Kir2.1 protein truncation alone does not result in pathogenicity. We propose missense variants in KCNJ2 exerting a dominant-negative effect could result in an ATS phenotype.