Jervell and Lange-Nielsen syndrome (JLNS), an autosomal-recessive variant of long QT syndrome characterized by deafness, significant QT prolongation (usually more than 500 ms), and a high risk of sudden death, is brought on by homozygous or compound heterozygous mutations in KCNQ1. The homozygous KCNQ1 c.520 C > T (p.R174C) mutation of case 5 was detected. The gene discussed is KCNQ1; the disease is Jervell and Lange-Nielsen syndrome.