The risk of arrhythmias is higher for those with<unk>  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 affected will die before the age of 15. However, treatment with beta blockers markedly reduces the risk of death, as does, in selected cases, implantation of a defibrillator.
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