Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Myotonia Congenita ?
    ### Response:
    Myotonia congenita is an inherited neuromuscular disorder characterized by the inability of muscles to quickly relax after a voluntary contraction. The condition is present from early childhood, but symptoms can be mild. Most children will be 2 or 3 years old when parents first notice their muscle stiffness, particularly in the legs, often provoked by sudden activity after rest.
    