Andersen-Tawil Syndrome

People who have Andersen-Tawil Syndrome (ATS) experience attacks of muscle weakness, and may also have irregular heart rhythm.

When it comes to potassium levels, there is a lot of inconsistency. Some attacks are associated with elevated blood potassium levels and in others the attacks are associated with low potassium levels.. Some episodes of weakness are triggered by eating a high-potassium meal, and other episodes are triggered by the patient not having enough potassium in their meals! Attacks usually begin before age 20.

Often, people with Andersen-Tawil Syndrome (ATS) 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. Short stature is also common in individuals with  ATS. Individuals with ATS can also have heart problems.  The most common presentation is the presence of a long QT interval on their EKG;  this can be associated with irregular heart rhythms.   It is always 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 when there is a need to treat both the attacks of muscle weakness and heart problems.

PP and Andersen-Tawil Syndrome

Periodic paralysis is a rare genetic disorder that is characterized by temporary attacks of transient muscle weakness or paralysis of variable severity. These attacks can be triggered by a variety offactors, 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 in a potassium channel that is essential for normal functioning of the muscle. 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 can also have abnormal heart rhythms, and they often have distinctive physical features as well.



People with Andersen-Tawil Syndrome have episodes of muscle paralysis.  Unlike other forms of periodic paralysis, it is often difficult to pinpoint what triggered the attacks, making it hard to find a consistent pattern from patient to patient, or even within a 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 a rise or fall in blood potassium levels but can also happen with normal blood potassium levels. The levels of rise or fall in potassium levels in ATS are not dramatic as in other forms of periodic paralysis and so treatment does not usually include lowering or raising the blood levels of potassium. 

This disorder is also known as long QT syndrome 7. Long QT syndromes are conditions in which the heart can develop irregular heart rhythms.  “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 as seen on an EKG. The prolongation of this period tends to trigger irregular heart rhythms. People with ATS may have long QT or other heart rhythm problems, and these problems can lead to fainting and rarely cardiac arrest.

ATS often comes with unusual physical characteristics such as a wide space between the eyes, a small jawline, a cleft palate, low-set 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 short stature. Patients might have some, all, or none of these traits. In addition, some patients have mild problems with thinking and learning. They might have difficulty staying focused, planning ahead, and thinking about abstract concepts. 



Individuals who have ATS  must become aware of what triggers their attacks so that they can try to avoid, or minimize the number of attacks of weakness. 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 ATS causes attacks that vary in severity and triggers, it is recommended that patients keep a diary to help them determine what triggers their attacks of weakness. 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 ATS  start experiencing symptoms before they turn 20.  Some will begin to have heart palpitations and fainting spells, while others may start having episodes of transient muscle weakness. Severity and frequency can vary greatly, and there are many possible triggers, so patients may not be able to pinpoint what triggers the episodes of weakness.  

As all forms of periodic paralysis are very rare diseases, most general practitioners will not be able to confirm the presence of periodic paralysis or to treat it.   All individuals with any form of episodic paralysis should be referred to a neurologist and preferably to a neurologist with neuromuscular training as they are the most likely to be familiar with periodic paralysis.

Giving doctors your family’s health history and your trigger diary can help them come closer to a periodic paralysis diagnosis. An important diagnostic test is the Long Exercise Test which measures the muscle’s response to exercise. This test can’t always detect periodic paralysis, but it can do so in a lot of cases. A positive long exercise test should result in genetic testing to find out if your DNA has a mutation in one of the genes that is associated with periodic paralysis.  This test is often the only necessary to make the diagnosis.

However, a negative genetic test may not rule out the possibility of having ATS since we know of a single gene that is associated with ATS and about 60% of individuals with ATS will have a mutation in that gene.  Consequently, if the DNA testing comes back negative, it is important make sure you don’t have any features of ATS. Because this disorder often causes longer than normal QT intervals in the heart rhythm, an EKG needs to be done 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 also learn about your family to see if they are other individuals with these symptoms: attacks of muscle weakness, heart rhythm problems, or distinct physical features.



Treatment for ATS  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.  It is also essential that the patient is followed by a neurologist experienced with managing patients with periodic paralysis as well as a cardiologist for regular follow-up to determine if and when they may need to be on heart medications to prevent irregularities in the heart rhythm.

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. ATS 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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