<unk>  causes severe sensorineural hearing loss from birth, affecting both ears. Those affected have a prolonged QT interval on an electrocardiogram and are at risk of abnormal heart rhythms (arrhythmias), which can cause dizziness, blackouts, or seizures. In general,<unk>  affects the heart more severely than other forms of long QT<unk> . 90% of those with<unk>  experience arrhythmias, with 50% becoming symptomatic by the age of 3. In some cases these arrhythmias lead to sudden death.
Jervell and Lange-Nielsen syndrome
Long QT syndrome
Fox–Fordyce disease
Andersen–Tawil syndrome
Laron syndrome
Cowden syndrome
Koolen–De Vries syndrome
Prader–Willi syndrome