Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Andersen-Tawil syndrome ?
    ### Response:
    Anderson-Tawil syndrome is a disorder that causes episodes of muscle weakness (periodic paralysis), changes in heart rhythm (arrhythmia), and developmental abnormalities. The most common changes affecting the heart are ventricular arrhythmia, which is a disruption in the rhythm of the heart's lower chambers, and long QT syndrome.
    