Abstract 638: A Novel Mutation In The KCR1 Gene May Influence Susceptibility To The Acquired Long QT Syndrome
Introduction: Acquired QT interval prolongation and torsade de pointes can be caused by exposure to certain drugs, electrolyte imbalance, and myocardial ischemia. Acquired LQTS is more prevalent than the congenital LQTS and represents a significant problem for public health. Previous reports showed that K+ channel regulator 1 (KCR1), an α glucosyltransferase, diminishes HERG drug sensitivity , and that a KCR1 polymorphism, Ile447Val, is associated with protection against drug-induced LQTS in humans. However, few studies address the effects of genetic changes in KCR1 and we screened the coding region of KCR1 in Japanese patients with the acquired LQTS.
Hypothesis: We hypothesized that mutations or polymorphisms in KCR1 may influence the development of acquired LQTS.
Methods: The genomic DNA of 70 unrelated patients with congenital LQTS, 41 unrelated patients with acquired LQTS, and 130 unrelated control subjects was screened by PCR-SSCP, PCR-RFLP, and direct sequencing. Appropriate sequence changes were introduced into subcloned KCR1 cDNA using site-directed mutagenesis, and HERG plus WT or mutant KCR1 cDNA was transiently transfected into CHO-K1 cells. HERG current was recorded using whole cell patch-clamp techniques and drug block of HERG current was assessed.
Results: We identified a novel mutation in KCR1, Glu33Asp in a Japanese acquired LQTS patient. Similar to what we reported previously, WT KCR1 diminished the susceptibility of HERG current to dofetilide (50 nM). After 15 min of continuous pulsing, 74±7% current remained in the presence of WT KCR1 vs 54±5% in the absence of KCR1. In contrast, 48±6% of HERG current remained in the presence of Glu33Asp KCR1 which was comparable to that of HERG alone. Significantly, we found that unlike WT KCR1, Glu33Asp KCR1 is no longer able to complement the genetic defect in α glucosyltransferase activity in yeast strain YG649, suggesting that enzymatic function of Glu33Asp KCR1 is compromised. We found no evidence for the Ile447Val KCR1 in Japanese LQTS patients and control subjects, which is present at an allele frequency of 7% allele frequency in a control population of the United States.
Conclusion: These data suggest that the Glu33Asp KCR1 genetic change may predispose to the development of acquired LQTS.