Myotonia Congenita

In Myotonia Congenita, the Chloride channels in muscles are not working properly. This is because of a ‘mistake’ in the gene that makes the chloride channel. This gene is called CLCN1

What is myotonia?

  • Myotonia is difficulty relaxing a muscle after it has been activated or contracted
  • It can feel like stiffness, cramps, locking and tightness.
  • It can sometimes be painful.
  • It can be experienced in all skeletal muscle including the legs, hands, chest and back
  • It can be hard to open the hands after holding things tightly.
  • The leg muscles are often affected the most and can lead to falls

What makes myotonia worse?

  • Myotonia can be made worse by different things for different people.
    • Commonly, starting an activity or movement is the most difficult. E.g. standing up and walking after sitting for a while
    • Cold weather
    • After exercise
    • Sitting still for a long time
    • Stress

What is the warm-up phenomenon?

  • In myotonia congenita, as the muscles are used or activated over and over, the myotonia often settles down and symptoms get better
  • For example when you first stand up and try to walk your legs may feel very stiff but the more steps you take they feel better and walking becomes easier


What are the different types of Myotonia congenita?

  • There are 2 types of Myotonia congenita:
    • Recessive myotonia congenita
    • Dominant myotonia congenita

  • Which type of myotonia congenita a person has determines how the condition is inherited.
    • Patients with recessive myotonia congenita would not be expected to pass on the condition to their children
    • Patients with dominant myotonia congenita have a 50% chance of passing it on to each child.
      (For more information about inheritance click here)