Gamstorp Disease (Hyperkalemic Periodic Paralysis)

Written by Cynthia Chase | Published on August 7, 2012
Medically Reviewed by George Krucik, MD

What is Gamstorp Disease?

Gamstorp disease is a very rare genetic condition that causes you to have episodes of muscle weakness or temporary paralysis. The disease is known by many names, including hyperkalemic periodic paralysis. The disease is inherited, and people can carry and pass on the defective gene without ever experiencing symptoms. Experts believe that only one in 250,000 people are affected. (HKPP, 2011)

Although Gamstorp disease is incurable, most people who have it are able to live fairly normal, active lives. Doctors have isolated many of the causes for the paralytic episodes and can usually help limit the disease’s effects by guiding patients to avoid certain triggers.

Causes and Risk Factors

Gamstorp disease is caused by a mutation in a gene, referred to as SCN4A, which produces sodium channels, or microscopic openings through which sodium and potassium are able to move through your cells. Muscle movement is controlled by electrical currents that are produced when different sodium and potassium molecules pass through cell membranes. With Gamstorp disease, these channels have physical abnormalities that cause potassium to gather on one side of the cell membrane and build up in the blood, preventing the needed electrical current from forming and causing you to become unable to move the affected muscle.

Gamstorp disease is autosomal dominant, which means that a child only needs to receive one copy of the mutated gene to develop the disease. If one of your parents is a carrier, there is a 50 percent chance you have the gene. However, some people who receive the gene never develop symptoms.

What are the Symptoms of Gamstorp Disease?

Gamstorp disease causes unique symptoms, including:

  • weakness of a limb
  • partial paralysis
  • irregular heartbeat
  • muscle stiffness
  • permanent weakness and immobility

Attachs of Paralysis

Paralytic episodes are short and may be over within a few minutes. Even when you are suffering from a longer episode, you should typically recover fully within two hours of the symptoms starting. However, the attacks often occur suddenly. You might find that you do not have sufficient warning to find a safe place to wait out an attack. For this reason, injuries from falls are common.

Attacks typically begin in infancy or early childhood. For most people, the frequency of the episodes increases through the adolescent years into the mid-twenties. As you approach your thirties, the attacks become less frequent. For some people, they disappear altogether.

Myotonia

One of the more devastating symptoms of Gamstorp disease is myotonia. If you have this problem, some of your muscle groups can become temporarily rigid and difficult to move. This can be very painful; however some people do not feel any discomfort during an episode. Because of constant contractions, the muscles affected by myotonia often look well-defined and strong, but you might find you are able to exert little or no force using these muscles. Myotonia causes permanent damage in many cases. Some people with Gamstorp disease are eventually confined to wheelchairs due to deterioration of their leg muscles, but treatment can often prevent or reverse progressive muscle weakness.

Diagnosis and Treatment

Gamstorp disease can be confirmed through blood tests, DNA analysis, or evaluation of serum electrolyte and potassium levels.

Treatment will vary based on the severity and frequency of your episodes. Many people respond well to medications and supplements, while others simply need to avoid certain triggers.

Medication

Most people have to rely on medication to control paralytic attacks. One of the more commonly prescribed medications is Diamox, a drug commonly used to control seizures. Your doctor may prescribe diuretics to limit the potassium levels in the blood. People with myotonia as a result of the disease can be treated using low doses of drugs such as Mexitil or Paxil, which help stabilize severe muscle spasms.

Other Treatments

People who experience mild or infrequent episodes can sometimes curb a paralytic attack without the use of medication. Mineral supplements, such as calcium gluconate, can be added to a sweet beverage to stop a mild episode. Drinking a glass of tonic water or sucking on a piece of hard candy at the first signs of a paralytic episode may help as well.

Avoiding Triggers

Some episodes can be triggered by potassium-rich foods or even certain behaviors. Too much potassium in the blood stream will cause muscle weakness even in people who don’t have Gamstorp disease—however, those with the disease may react to very slight changes in potassium levels that would not affect the average person.

Common triggers include:

  • fruits high in potassium, such as bananas, apricots, figs, and raisins
  • potassium-rich vegetables such as spinach, potatoes, broccoli, and cauliflower
  • lentils, beans, and nuts
  • alcohol
  • long periods of rest or inactivity
  • going too long without eating
  • extreme cold or heat

Note that not everyone with Gamstorp disease will have the same triggers.

Long-Term Outlook

By carefully managing your risk factors, you can moderate the effects of the condition, while aging actually reduces the frequency of the episodes. It’s important to talk to your doctor about foods and activities that might be causing your episodes. Because Gamstorp disease is hereditary, it cannot be prevented. However, by avoiding the triggers that cause the paralytic episodes, you can limit the disease’s effects.

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