The present invention describes an association between genetic polymorphismsin the FAM13A1 (family with sequencesimilarity 13, member Al) gene and a predisposition to prolongation of the QTinterval, and provides related methods forthe prediction of such a predisposition, the administration of QT interval-prolonging compounds to individuals having such apredisposition, and determining whether a compound is capable of inducing QTprolongation.