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Gamstorp disease is an extremely 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. It’s an inherited disease, and people can carry and pass on the defective gene without ever experiencing symptoms. One in 250,000 people have this condition.
Although there’s no cure for Gamstorp disease, most people who have it can live fairly normal, active lives. Doctors know many of the causes for the paralytic episodes and can usually help limit the disease’s effects by guiding people with this disease to avoid certain identified triggers.
Gamstorp disease causes unique symptoms, including:
Paralytic episodes are short and may end after a few minutes. Even when you have a longer episode, you should typically recover fully within two hours of the symptoms starting. However, episodes often occur suddenly. You might find that you don’t have sufficient warning to find a safe place to wait out an episode. For this reason, injuries from falls are common.
Episodes typically begin in infancy or early childhood. For most people, the frequency of the episodes increases through the adolescent years and into their mid-20s. As you approach your 30s, the attacks become less frequent. For some people, they disappear altogether.
One of the symptoms of Gamstorp disease is myotonia. If you have this symptom, some of your muscle groups can become temporarily rigid and difficult to move. This can be very painful. However, some people don’t 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 can only exert little or no force using these muscles. Myotonia causes permanent damage in many cases. Some people with Gamstorp disease eventually use wheelchairs due to deterioration of their leg muscles. Treatment can often prevent or reverse progressive muscle weakness.
Gamstorp disease is the result of a mutation, or alteration, in a gene called "SCN4A." This mutation produces sodium channels, or microscopic openings through which sodium and potassium move through your cells. Electrical currents produced by different sodium and potassium molecules passing through cell membranes control muscle movement.
In 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. This prevents the needed electrical current from forming and causes you to become unable to move the affected muscle.
Gamstorp disease is an inherited disease, and it’s autosomal dominant. This means that you only need to have one copy of the mutated gene to develop the disease. There’s a 50 percent chance you have the gene if one of your parents is a carrier. However, some people who have the gene never develop symptoms.
To diagnose Gamstorp disease, your doctor will first rule out adrenal disorders such as Addison’s disease, which occurs when your adrenal glands don’t produce enough of the hormones cortisol and aldosterone. They’ll also attempt to rule out genetic kidney diseases that can cause low potassium levels.
Once they rule out these adrenal disorders and inherited kidney diseases, your doctor can confirm if it’s Gamstorp disease through blood tests, DNA analysis, or by evaluating your serum electrolyte and potassium levels.
To evaluate these levels, your doctor may have you do tests involving moderate exercise followed by rest to see how your potassium levels change. Someone with Gamstorp disease will see high potassium levels during exercise that reduce during rest and rise again 20 minutes after stopping the exercise.
If you think you may have Gamstorp disease, it may help to keep a diary tracking your strength levels throughout each day. You should keep notes about your activities and diet on those days to help determine your triggers. You should also bring any information you can gather about whether or not you have a family history of the disease.
The treatment is based on the severity and frequency of your episodes. Medications and supplements work well for many people who have this disease. Avoiding certain triggers works well for others.
Most people have to rely on medication to control paralytic attacks. One of the more commonly prescribed medications is acetazolamide (Diamox), which is 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 mexiletine (Mexitil) or paroxetine (Paxil), which help stabilize severe muscle spasms.
People who experience mild or infrequent episodes can sometimes curb a paralytic attack without the use of medication. You can add mineral supplements, such as calcium gluconate, 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.
Potassium-rich foods or even certain behaviors can trigger episodes. Too much potassium in the bloodstream 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 wouldn’t affect someone who doesn’t have Gamstorp disease.
Common triggers include:
Not everyone with Gamstorp disease will have the same triggers. Talk to your doctor and try recording your activities and diet in a diary to help determine your specific triggers.
You can moderate the effects of the condition by carefully managing your risk factors. Aging 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, you can’t prevent it. However, avoiding the triggers that cause the paralytic episodes can limit the disease’s effects.
Written by: Cynthia Chase
Medically reviewed on: Mar 18, 2016: Steve Kim, MD
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