Andersen-Tawil Syndrome

People who have Andersen-Tawil Syndrome (ATS) experience muscle weakness attacks, but they also experience some feelings of muscle weakness between attacks.

When it comes to potassium levels, there is a lot of inconsistency. Some attacks cause the patient’s potassium to rise, and other attacks cause it to fall. Some attacks are triggered by eating a high-potassium meal, and other attacks are triggered by the patient not having enough potassium in their meals! Attacks usually begin before age 20.

Often, people with Andersen-Tawil Syndrome show physical signs of the disorder in their body shape. They might have two toes that are “webbed” together, a finger that is slightly bent, widely-set eyes, and low-set ears. Another Andersen-Tawil Syndrome symptom is problems with heart rhythm. This should show either significantly or minorly as a long QT interval on an EKG. It is often necessary to involve the help of an Electrophysiology Cardiologist in making this diagnosis. Medications can be used to treat this disorder, but figuring out the right medications can be complicated because both the muscle weakness attacks and the heart problems need to be treated.

PP and Andersen-Tawil Syndrome

Periodic paralysis is a rare genetic disorder that is characterized by temporary attacks of extreme muscle weakness or paralysis. These attacks can be triggered by a variety of things, with the most common triggers being resting after exercise, cold temperatures, and having too much or too little potassium. There are several types of periodic paralysis. Understanding the different types can be difficult, but we are here to give you guidance.

Periodic paralysis is caused by muscle cells that do not have the right balance of chemicals to work properly. Muscle cells have openings called channels that open and close to let particles such as sodium, potassium, and calcium go in and out. These particles are called ions, and muscle cells can only work if the right kinds of ions enter and exit the cells at the right times. When the channels don’t open and close the way they’re supposed to, the ions become imbalanced, and muscles aren’t able to function normally.

Andersen-Tawil Syndrome (ATS), also known as long QT syndrome 7, is a genetic disorder in which patients experience muscle weakness and paralysis attacks that are caused by a mutation on potassium channels. Attacks can be triggered by high blood potassium levels or low blood potassium levels, and during attacks, potassium may rise, fall, or remain normal. People with this disorder also have abnormal heart rhythms, and they often have distinctive physical features as well.



People with Andersen-Tawil Syndrome have muscle weakness and paralysis attacks, and there are many factors that vary with these attacks, so it can be hard to find a consistent pattern from patient to patient, or even within one single patient. Attacks can last anywhere from a few minutes to a few hours, and some attacks stretch on for days. The legs and arms are most often affected. Sometimes, the patient’s muscles are weak and heavy, but other times, the muscles are completely paralyzed. There also tends to be mild weakness between attacks. After many years, the patient may eventually develop permanent muscle weakness (myopathy).

The relationship between Andersen-Tawil Syndrome and potassium is inconsistent, and it varies between patients. It’s also possible for one patient to have different experiences at different times. Some attacks are caused by the patient having too much potassium in their blood (hyperkalemia), while other attacks are caused by the patient not having enough potassium in their blood (hypokalemia), and there are additional triggers as well. Potassium may rise or fall during attacks, or it can stay at a normal level. Taking potassium supplements can reduce weakness or increase it.

This disorder is also known as long QT syndrome 7. Long QT syndromes are a group of heart rhythm conditions that involve the electric waves the heart produces on an electrocardiogram (EKG). “Long QT” means that there is a longer than normal period of time between the start of the Q wave and the end of the T wave. People with Andersen-Tawil Syndrome may have long QT or other heart rhythm problems, and these problems can lead to fainting, or more rarely, cardiac arrest. However, it is unlikely that heart problems caused by this disorder will be life-threatening.

Andersen-Tawil Syndrome often comes with unusual physical characteristics such as a wide space between the eyes, a small jawline, cleft palate, low ears, fingers that are crooked (most likely a pinky finger that is bent sideways toward the other fingers), webbed toes (most likely between the second and third toes), a curved spine, and very short stature. Patients might have some, all, or none of these traits. In addition, some patients have problems with thinking and learning. They might have difficulty staying focused, planning ahead, and thinking about abstract concepts. 



People who have Andersen-Tawil Syndrome must become aware of what kinds of things trigger their attacks so that they can try to avoid those things. Potassium-rich foods can sometimes be a trigger, but other times, attacks are triggered by not having enough potassium. Eating too much or too little can cause an attack to occur. Being cold is likely to trigger an attack, so it’s best to live in a warm climate and stay away from strong air conditioning. Even emotions can trigger attacks — stressful emotions are a major trigger.

Another very common attack trigger is exercise followed by a period of rest. The body has difficulty recovering from the exertion, and an attack occurs. This is especially likely if the exercise was intense. On the other hand, inactivity can be a trigger as well. Sitting for a long time can lead to a weakness attack that makes it difficult to stand up and walk away. In addition, sleep is a trigger because it is common for patients to sleep for a while, then experience weakness or paralysis when they wake up.

Because Andersen-Tawil syndrome causes attacks that vary in terms of how severe they are and what triggers them, it is recommended that patients keep a trigger diary. Here’s how: After you have an attack, you should write down what happened, how you felt, what you were doing before the attack, and how you were able to recover from it. After doing this for a while, you’ll be able to look back on your previous diary entries and possibly notice certain patterns. Even if there are no clear patterns, the diary will be useful to discuss with your doctor.



Most people who have Andersen-Tawil Syndrome start experiencing symptoms before they turn 20. They will begin to have heart palpitations and fainting spells, as well as muscle weakness and paralysis attacks. Attack severity and frequency can vary greatly, and there are many possible triggers, so patients may not understand what is going on and why it is happening. 

Doctors usually aren’t familiar with this rare disorder, so they might incorrectly diagnose the patient with a disorder that’s more common. This leads to the patient not receiving the right kind of care and treatment. Having the correct diagnosis of periodic paralysis is necessary for proper treatment. However, because there are multiple types of periodic paralysis, it’s important for the doctor to recognize when a patient has Andersen-Tawil Syndrome specifically.

Giving doctors your family’s health history and your trigger diary can help them come closer to a periodic paralysis diagnosis, and there are other diagnostic tools available, too. A muscle biopsy is sometimes needed for doctors to diagnose periodic paralysis. This means that the doctor must remove and examine a small piece of the patient’s muscle tissue during or after an attack to see if the muscle tissue is abnormal. Another diagnosis method is the Compound Muscle Action Potential test, which measures the electrical activity of muscles. This test can’t always detect periodic paralysis, but it can do so in a lot of cases. 

If you have been diagnosed with periodic paralysis, you should also be screened for Andersen-Tawil Syndrome. Because this disorder often causes longer than normal QT intervals in the heart rhythm, an EKG needs to be used so that the doctor can analyze your heart’s electrical activity. Your doctor should also examine your physical characteristics in order to check for the distinctive facial and body structures that many people with this disorder have. Your doctor needs to learn about your family as well to see if they have one or more of these symptoms: muscle weakness attacks, heart rhythm problems, or distinct physical features.



Treatment for Andersen-Tawil Syndrome is complicated because different patients have different symptoms, and what helps one patient might hurt another. For this reason, it is crucial that doctors come up with an individualized treatment plan for each patient. Complicating things even further is the fact that treatments must address both the heart rhythm abnormalities and muscle weakness attacks, and some treatments can ease one problem and worsen the other. There is some trial-and-error involved in developing the best treatment strategy for a patient.

The drug acetazolamide is likely to help with muscle weakness attacks, as well as dichlorphenamide (brand name KEVEYIS, the only FDA-approved periodic paralysis treatment). Taking potassium supplements can help patients whose attacks are triggered by not having enough potassium in their blood. On the other hand, patients whose attacks are triggered by high potassium may be able to shorten the length of attacks by having a high-carb food or beverage during an attack.

Lifestyle changes are important, too. Andersen-Tawil syndrome patients should try to avoid being in cold environments, and they should also be careful when exercising so that they are not overexerting themselves. Stress management also plays a big role in reducing the chances of an attack. It’s helpful to have healthy ways to cope with stressful situations. Changes in diet may be necessary, because certain foods may trigger attacks.


Special heart medications are needed to address heart rhythm problems. Beta-blockers such as propranolol, anti-arrhythmics such as flecainide, and calcium-channel blockers such as verapamil are possible options, but some of these heart medications could make muscle weakness worse, so caution is needed. Also, people with this disorder should avoid medications that can make their heart’s long QT interval even longer. Credible Meds has created a list of these medications, although ultimately, a doctor’s guidance is necessary.


Your Next Steps

If you think you may have Andersen-Tawil Syndrome, please talk with your doctor. Speaking with a doctor about a rare disorder can be intimidating, and many doctors have little to no prior knowledge about periodic paralysis. The PPA has many resources to help you become a better advocate for yourself. Click here to learn about other types of periodic paralysis. You can also submit a question to our Ask the Experts panel. Remember, we are here to support you all the way as you take action to advocate for your health!

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