What Is Familial Chylomicronemia Syndrome (FCS)?

Familial chylomicronemia syndrome, or FCS, is a metabolic disorder. This means it is a problem with how the body processes substances to make energy. FCS is a genetic condition. It is passed down in families. It is not something you "catch."¹

FCS is extremely rare. It affects only about 1 to 2 people out of every 1 million worldwide. Because it is so rare, many people struggle for years to get a correct diagnosis. The condition centers on how your body handles fat. Symptoms can include:¹

• Severe abdominal pain
• Nausea and vomiting
• Bloating
• Fatigue
• Brain fog

What causes FCS?

When you eat food, your body digests the fats, which are called triglycerides. These fats are packaged into large particles called chylomicrons. Chylomicrons then travel through your blood to give your body energy.¹

A healthy body makes a special enzyme called lipoprotein lipase, or LPL. The job of LPL is to act like scissors. It breaks down the chylomicrons and clears the triglycerides from the blood.¹

People with FCS have a genetic defect, or mutation. This mutation means their body cannot make LPL that works. About 8 out of 10 people with FCS have a problem with the LPL gene itself. Other, even rarer, cases are caused by mutations in genes that help LPL do its job.¹

Without working LPL, the body cannot break down the chylomicrons. The fat from your food has nowhere to go. The chylomicrons and triglycerides build up in the blood to extremely high levels.¹

What are the complications of FCS?

A normal fasting triglyceride level is below 150 mg/dL. A very high level is 500 mg/dL. People with FCS often have fasting triglyceride levels over 1,000 mg/dL. Sometimes their levels are 10 to 100 times higher than normal.¹

This severe, milky-white fat in the blood is very dangerous. It puts a person at high risk for acute pancreatitis.^1,2

Acute pancreatitis is a sudden, painful swelling of the pancreas. The pancreas is an organ behind your stomach. The high levels of fat can damage this organ, causing severe pain. This pancreatitis is the most serious complication of FCS. It can happen over and over again. These recurrent attacks can lead to long-term damage. Acute pancreatitis is a medical emergency that can be life-threatening. It may require a hospital stay and can sometimes be fatal if left untreated.^1,2

FCS is not a lifestyle condition

This is the most important point for you to understand. FCS is not the result of an unhealthy, high-fat diet. FCS is a monogenetic disorder. This means it is caused by a defect in a single gene. It is not caused by lifestyle choices. People with FCS can have symptoms even with a low body weight. They often get sick as children, long before lifestyle factors are a problem.^1,2

Standard medicines used to lower triglycerides in MCS, such as fibrates or statins, often do not work for people with FCS. This is because those drugs require a working LPL system. People with FCS do not have one.^1,2

How is FCS treated?

For years, the main treatment for FCS has been a very strict, low-fat diet. Recently, new drugs have been developed to help manage the condition. In 2024, the U.S. Food and Drug Administration (FDA) approved Tryngolza™ (olezarsen). It is the first drug approved for adults with FCS in the United States.³

Tryngolza works by lowering the body's production of a protein called apoC-III. This protein is a key regulator of fats in the blood. By reducing this protein, the drug helps lower high triglyceride levels and significantly reduces attacks of acute pancreatitis. This drug is used in addition to a low-fat diet to help lower triglycerides and is self-administered as an injection once a month.³

Another drug, Waylivra® (volanesorsen), was approved in Europe in 2019. However, it is not available in the US.⁴

What this means for you

Understanding FCS is the first step toward managing it. FCS is an ultra-rare genetic disorder that prevents the body from breaking down dietary fat. This leads to extremely high triglyceride levels in the blood. This buildup causes a high risk of frequent, painful, and life-threatening acute pancreatitis, among other symptoms.^1,2

FCS is a lifelong medical condition. It is not caused by poor lifestyle choices. If you have a history of severe abdominal pain and very high triglycerides, talk to your doctor. Ask if your symptoms could be caused by FCS.