In summary, the genetic and molecular analyses of this work have confirmed the index patient’s diagnosis of Jervell and Lange-Nielsen syndrome 1 (JLNS1) by the identification of biallelic variants in the KCNQ1 gene, p.R259L and a previously undescribed intronic variant c.1686−9 T > C. This evidence concerns the gene KCNQ1 and Jervell and Lange-Nielsen syndrome.