Familial Hyperchylomicronemia Syndrome (FCS)

Written by Rachel Reiff Ellis
Medically Reviewed by Neha Pathak, MD on January 09, 2025
12 min read

Familial hyperchylomicronemia syndrome (FCS) is a rare disorder you get from genes passed down from your parents. When you have it, your body isn’t able to break down (metabolize) fat. Specifically, FCS prevents you from breaking down fats (lipids) called triglycerides. Sometimes FCS is called lipoprotein lipase deficiency. 

When you have FCS, fatty droplets called chylomicrons build up in the plasma of your bloodstream. Chylomicrons help move triglycerides to different parts of your body for energy and fat storage. When chylomicrons build up, this is called chylomicronemia syndrome. Chylomicronemia syndrome causes increased levels of triglycerides in your bloodstream. 

Typically, FCS causes symptoms that affect your quality of life such as pain and inflammation of certain organs. 

Only one to two people per million have FCS. You can get it at any age, although it’s more common to get a diagnosis before age 10. Around 25% of people with FCS get a diagnosis in their first year of life. It affects all genders, races, and ethnicities equally. 

The primary way to help manage the disorder is through diet. 

FCS happens because of a mutation in certain genes related to an enzyme called lipoprotein lipase (LpL). You have to get the mutated gene from both your parents to have the disorder. If you get only one gene with the mutation, you’re a carrier for the disease but won’t have the disorder yourself. But you may be at a higher risk of other health disorders caused by abnormal levels of lipids in the blood. 

Researchers know of at least six genes related to FCS. The disorder happens when you get a mutation in any of these genes. Some of these genes help encode LpL itself, and some encode other proteins that help LpL work correctly. Mutations in these genes either mean you don’t have LpL at all in your body or your LpL can’t work the way it should.

Enzymes are proteins that speed up processes in the body. Your pancreas makes the LpL enzyme. Normal LpL breaks down chylomicrons in your bloodstream so your body can use them for energy. When LpL doesn’t work the way it should, or you don’t have enough LpL, your body can’t break down fat and your chylomicron levels – and therefore, your triglyceride levels – skyrocket.

The symptoms you get from FCS are caused by the high levels of triglycerides in your bloodstream. A normal triglyceride blood level is less than 150 milligrams per deciliter (mg/dL). When you have FCS, it’s common to have a triglyceride level of 1,000 mg/dL. This level can change drastically based on how much fat is in your diet. 

Common symptoms of FCS include:

  • Abdominal pain. This is the most common symptom of FCS. Typically the pain comes in episodes and can range from mild to severe. Usually the pain happens in the upper central part of your belly area, and it may spread to your back. 
  • Pancreatitis. Pancreatitis is the inflammation of your pancreas, the organ behind your stomach that makes hormones and digestive enzymes. Often the abdominal pain of FCS is related to pancreatitis. It’s common to also have nausea, sweating, weakness, chills, and slight yellowing of the skin and eyes.
  • Skin changes. About half of all people with FCS will get a condition called cutaneous xanthomas, which causes painless, raised, reddish-yellow bumps on the skin of your bottom, knees, and outer arms. These bumps are made of lipids. When you see these bumps, it can be a sign that your triglyceride levels are going up. They typically go away as triglyceride levels go down.
  • Eye changes. Lipaemia retinalis is an eye condition that causes a milky appearance of the blood vessels in your eye. This milky look happens because of fatty buildup. It goes away when lipid levels decrease and doesn’t affect your vision.
  • Enlarged liver and spleen. Infants and young children are at risk of making extra white blood cells called macrophages. Macrophages try to reduce excess fat in the body by absorbing fat cells and turning them into foam cells. Foam cells build up in the liver, and spleen, making them bigger.
  • Neuropsychiatric symptoms. Some people with FCS have depression, memory loss, and dementia.

Research shows that people with FCS see an average of five doctors before getting a diagnosis. This is in part because it’s so rare and doesn’t have a universal set of criteria for diagnosis. 

Endocrinologists (doctors who treat hormone disorders) and lipidologists (doctors who treat cholesterol and blood fat disorders) are the specialists who typically treat FCS. You could also get a diagnosis from a geneticist. You may also see a gastroenterologist because of your abdominal pain, who can help diagnose you. 

Your doctor may suspect you have FCS if you have:

  • A history of abdominal pain
  • Multiple bouts of pancreatitis
  • High triglyceride blood count (hypertriglyceridemia)
  • Diabetes 
  • Medications that are known to cause hypertriglyceridemia
  • High triglycerides with no other cause (such as excessive alcohol intake)

If you have these signs, they may give you certain tests to gather more information.

Tests for familial hyperchylomicronemia syndrome

To give you an official diagnosis of FCS, your doctor may give you tests such as:

Fasting triglyceride blood test. To do this test, your doctor will ask you not to eat for a certain number of hours before drawing a blood sample. A lab will look at the level of triglycerides in your blood. If your levels are 750 mg/dL or above, you may have FCS. The extra lipids in your blood may also make it look milky. 

Lipase level test. This test looks at how much LpL your body releases. Your doctor gives you a dose of heparin through an IV. Heparin tells your body to release LpL. If your levels don’t go up after you get heparin, it tells your doctor your body isn’t making it. 

Genetic tests. Your doctor can confirm you have FCS with a genetic test to see if you have the genetic mutation for the condition from both parents. The common mutations geneticists look for are:

  • LpL
  • Apolipoprotein C2 (APOC2)
  • Lipase maturation factor 1 (LMF1)
  • Apolipoprotein A5 (APOA5)
  • Glycosylphosphatidylinositol-anchored high-density lipoprotein (HDL)-binding protein 1 (GPIHBP1)

CT scan. In some cases, your doctor may want to give you a CT scan (computerized tomography scan) to help confirm a diagnosis. A CT scan can show your doctor if you have an enlarged spleen or liver, or if you have pancreatitis.

In December 2024, the FDA approved the first medication for treating FCS. Olezarsen (Tryngolza) is a shot you take under the skin once a month. It’s a specially designed molecule that attaches to the genetic instructions (mRNA) for making a protein called apoC-III. 

Once olezarsen binds to this mRNA, it causes the mRNA to break down. Without the mRNA, the body makes less of the apoC-III protein.

Since apoC-III protein usually slows down the removal of certain fats (like triglycerides and very low-density lipoproteins, or VLDL) from the blood, lowering apoC-III helps the body clear these fats more efficiently. This can help reduce the levels of these fats in the blood.

Treatments for other lipid disorders that reduce lipid levels, such as statins, fibrates, and niacin, won’t work on FCS. These medications rely on your body having a functioning lipoprotein lipase enzyme in order to work.

Familial hyperchylomicronemia syndrome diet

To help manage your FCS, your doctor will recommend you limit your fat intake to less than 20 grams a day, or less than 10% to 15% of your total calories for the day. An FCS diet also means avoiding alcohol and limiting simple carbohydrates like the ones you get in candy and soda. 

Foods to eat when you have FCS include:

  • Vegetables
  • Fruits
  • Whole grains
  • Egg whites
  • Legumes
  • Fat-free dairy products
  • Seafood
  • Lean poultry

You need some essential fatty acids for your body to function. The best way to get these when you have FCS is by taking supplements with fat-soluble vitamins (A, D, E, and K). Talk to your doctor about whether a diet rich in medium-chain fatty acids can help treat FCS. You can find medium-chain fatty acids in:

  • Coconut oil
  • Milk fat
  • Palm kernel oil

It’s also best to eat small meals more often and larger meals less often. These small meals should have fat-free or low-fat protein. Your doctor can recommend a registered clinical dietitian to help you learn and maintain an FCS diet. 

Some medications can increase triglyceride levels. Talk to your doctor to see if you need to reduce or stop taking these medications:

  • Diuretics
  • Steroids
  • Estrogen
  • Blood pressure medications
  • Immune system suppressants
  • Antidepressants
  • Certain heart medications
  • Fish oil supplements

Many of the complications of FCS happen when you have repeated bouts of pancreatitis. When pancreatitis happens often, your pancreas may have trouble working the way it should. This could lead to complications such as: 

Diabetes. Your pancreas makes insulin, and damage to your pancreas over time disrupts this process. Without enough insulin, you can get diabetes and have to take insulin as a medication.   

Cardiovascular disease. When your triglycerides stay at high levels, it affects your artery walls and increases your risk of heart and vessel problems.

Pancreatic pseudocyst. Leaking pancreatic fluid can collect and form sacs next to your pancreas. Sometimes they don’t cause any symptoms, and other times they cause pain, bloating, fever, nausea, and vomiting. 

Multiorgan failure. If you have a severe bout of pancreatitis, it can cause other organs to shut down. This increases your chances of further complications and even death.

After you’ve gotten an FCS diagnosis, you’ll have many questions. You may want to know:

  • How did I get FCS?
  • Should I see a specialist to help treat my FCS?
  • Should my family members be tested for FCS, even if they don’t have symptoms?
  • What are my treatment options?
  • What is the goal of treatment? 
  • How soon should I see changes in my triglyceride levels?
  • How does FCS increase my risk of pancreatitis, and what should I do if I have abdominal pain?
  • How often should I have my blood triglyceride levels checked?
  • What is my target triglyceride level?
  • Do any of my other health conditions or medications affect my FCS?
  • What are serious symptoms I need to know about right away?
  • How will this affect my quality of life?

Gather as much information as you need to take an active part in your FCS management.

It can take a while to get an FCS diagnosis, but once you know what you have, spend time getting to know what to expect and what it means to have this condition. Having FCS can have a big impact on your life. Managing it takes a lot of effort. It can be common to deal with issues such as:

  • A hard time eating at restaurants 
  • Higher food costs
  • More time preparing food
  • Mental and physical fatigue 

Aside from the physical symptoms, you may also deal with the mental and emotional toll of living with the disease. You may have:

  • Trouble concentrating
  • “Brain fog”
  • Anxiety about your health
  • Worry about how you’ll manage FCS the rest of your life
  • Fear 
  • Stress

It’s possible you’ll need to go to the hospital because of your condition, and this can make it hard to keep social engagements and work obligations. Around 75% of people with FCS report that it restricts their social life. Nearly 94% of people with the disease who are unemployed or underemployed point to FCS as the cause. 

Staying connected with your care team – especially a registered clinical dietitian and a mental health professional – can better help you navigate life with FCS.

As you work with your care team to manage your FCS, be sure you’re also adopting habits that can help you live as fully as possible. This includes:

Educate yourself. Studies show the more you know about FCS, the more likely you are to stick to treatment and lifestyle habits that support people who have FCS. Ask your doctor where you can learn more, and come prepared with your questions when you go to doctor visits. 

Tap into help. Don’t try to go it alone. Professionals can help with diet and disease management, but loved ones can be a source of support, too. Ask for help with diet and lifestyle changes you need to make to live well with your disease. Make sure others know what FCS is and how they can be part of your team. 

Cut out alcohol. Alcohol will increase your triglycerides. It’s not enough to reduce your alcohol consumption; you need to avoid it completely.

Be vigilant. Tell your doctor right away if you begin having more FCS symptoms so they can be addressed quickly.

Follow your treatment plan. If you don’t treat your condition, the complications can be serious and life-threatening.

FCS is rare, but there are others out there dealing with it. Connecting with those who “get it” can help you feel less alone and also provide tips and advice for living well with the condition. 

The FCS Foundation is an organization that offers education, advocacy, and support for people living with the condition. It was created by people directly affected by FCS, either themselves or as parents of children with the condition. The FCS Foundation has an active social media group, a medical advisory board, and a monthly newsletter to help you stay informed.

Other organizations, such as the National Organization for Rare Disorders, can help people living with rare conditions. They provide financial and logistical resources for those navigating life with a rare disease.

Living with a chronic condition, especially one that affects your life so fully, can have a profound impact on your mental and emotional health. It’s important to find a way to plug into mental health care, whether that’s through group support or individual therapy. 

Make your emotional health a regular part of your conversation with your doctor as you manage your FCS. When you're struggling with your emotional health, it’s harder to stay on top of your condition management. Try these tips:

Connect with a counselor. There are many options, including virtual appointments through mental health care apps, trained counselors you see in person, cognitive behavioral therapists, psychologists, and even psychiatrists who can help with medical management of depression, anxiety, and other mental health issues.

Move your body. Regular physical activity boosts your mood and supports mental health.

Open up. Talk to trusted loved ones about how living with FCS affects you. Create a mental support network to buoy you when needed.

Find fun. Prioritize a hobby you enjoy, foster social connections, and seek out the big and small things that bring meaning and pleasure to your life.

Caring for someone with a rare condition has challenges. But there are ways you can support your loved one’s care while also caring for yourself. 

Learn what you can. You’re a better caregiver when you know what you’re helping care for. Educate yourself on FCS: how it impacts your loved one and what kind of care they need to live a full life. 

Find your own support. If you’re caring for someone with FCS, especially if you’re a parent helping a child live with the condition, you may find it helpful to plug into a caregivers network. There are many support groups for people caring for others. These include:

  • Family Caregiver Alliance
  • National Alliance for Caregiving
  • Caregiver Action Network
  • National Family Caregiver Support Program
  • The Caregiver Space

Advocate for your loved one. Come to medical visits and take notes. Ask questions and clarify things you don’t understand. Be an active part of your loved one’s care team.

FCS is a rare genetic disorder preventing the normal breakdown of triglycerides. It’s caused by a mutation in genes related to the lipoprotein lipase (LpL) enzyme. When you have it, triglycerides build up in your bloodstream. 

Symptoms include abdominal pain, pancreatitis, skin and eye changes, and issues with your thinking skills. In December 2024, the FDA approved a once-a-month shot to help treat FCS along with changes to your diet.

FCS can have a big impact on daily life, bringing frequent pain, fatigue, anxiety, and dietary restrictions and creating social, emotional, and economic challenges. Support groups, emotional health care, and regular monitoring can help you manage your condition.

Is FCS a rare disease?

Doctors consider FCS a rare disease because it affects only one to two out of every million people. 

What foods should you avoid if you have familial hyperchylomicronemia syndrome?

Because managing the disease means strictly limiting the amount of fat in your diet, you shouldn’t eat foods with high fat, even healthy fat. Simple-sugar foods such as candy, soda, or juice also pose a risk. 

What is the life expectancy for someone with familial hyperchylomicronemia syndrome?

While you can manage the disease for life with diet, FCS can increase your risk of complications that can reduce your life expectancy. Pancreatitis is the main life-limiting issue.

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