leading to the hearing loss and irregular heart rhythm characteristic of Jervell and Lange-Nielsen syndrome. Diagnosis The sensorineural hearing loss in Jervell and Lange-Nielsen syndrome is present from birth and can be diagnosed using audiometry or physiological tests of hearing. The cardiac features of JLNS can be diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. In those with Jervell and Lange-Nielsen syndrome the QTc is typically greater than 500 ms. Other factors beyond the QT interval should be taken into account when making a diagnosis, some of which have been incorporated into scoring systems such as the Schwartz score. These factors include a history of characteristic abnormal heart rhythms (Torsades de Pointes), unexplained blackouts (syncope), and a family history of confirmed LQT syndrome. Genetic testing to identify variants in the KCNQ1 or KCNE1 genes can also be used. Treatment The risk of arrhythmias can be reduced in several ways. Medications that further prolong the QT interval such as sotalol should be avoided, as should very strenuous or competitive exercise. Blood potassium levels should be kept within the normal range. Potassium supplements may be used at times when potassium is being lost such as when experiencing diarrhoea or vomiting, but medications that encourage the retention of potassium such as spironolactone or amiloride may also be required. Beta blockers such as propranolol or nadolol reduce the risk of arrhythmias. An implantable defibrillator, a small device that monitors the heart rhythm and can automatically deliver an electric shock to restart the heart, may be used. These devices are recommended for those with JLNS who have experienced a cardiac arrest or a blackout whilst taking beta blockers. Due to the higher risk of arrhythmias associated with JLNS than other forms of long QT syndrome, a defibrillator may be considered even in those without any symptoms. In those who experience recurrent arrhythmias despite medical therapy, a surgical procedure called sympathetic denervation can be used to interrupt the nerves that stimulate the heart. Prognosis The risk of arrhythmias is higher for those with Jervell and Lange-Nielsen syndrome than other forms of long QT syndrome. Although this risk is dependent on the underlying genetic defect and degree of QT prolongation, without treatment more than 50% of those