Any Jervell and Lange-Nielsen syndrome in which the cause of the disease is a mutation in the KCNQ1 gene. The disease is Jervell and Lange-Nielsen syndrome 1 (MONDO_0024540). Also known as: Jervell and Lange-Nielsen syndrome caused by mutation in KCNQ1, KCNQ1 Jervell and Lange-Nielsen syndrome.