Not an actual patient.
Understanding FCS
An overview of Familial Chylomicronaemia Syndrome (FCS) and what a diagnosis can involve
FCS is a rare, inherited condition,
affecting around 1–2 people per million1
What causes FCS?
FCS is a genetic condition that develops when a person inherits an affected gene. Although FCS is present from birth, diagnosis can happen at any age. Some people are identified early in life, while others may experience symptoms for years before receiving a diagnosis.1
When you have FCS, your body has a problem clearing triglycerides, a kind of fat that comes from the food you eat and is carried in particles called chylomicrons.2,3
One of the key proteins that normally works to break down triglycerides in your blood is lipoprotein lipase (LPL). In people with FCS, LPL is either missing or doesn’t work properly.2,4
Triglycerides, therefore, build up in your blood instead of being broken down, leading to very high triglyceride levels.2,4
Symptoms of FCS
FCS is often an invisible condition. You may appear healthy, but you could be living with symptoms that significantly affect daily life. Because these symptoms are often mistaken for other conditions, diagnosis and access to support may be delayed.5
If you have FCS, you may experience a range of signs and symptoms. The most commonly reported symptom is abdominal pain, which can range from mild to severe and is usually felt in the upper abdomen. The most serious symptom is acute pancreatitis. This occurs when the pancreas becomes inflamed and causes pain, typically felt in the upper left side or middle of the abdomen.4,5
Diagnosing FCS
Diagnosing FCS can be challenging.6 Although the condition is present from birth, your symptoms and their onset may vary and can be mistaken for other causes of very high triglycerides, such as those related to diet, lifestyle, or other medical conditions.5,8,9 For some, symptoms may begin later on. Your healthcare professional may first rule out these more common causes before considering a specific underlying condition such as FCS.9 Because FCS is rare, it may take time for the condition to be recognised.6,7
When assessing FCS, your healthcare professionals may consider factors such as:6,7
Very high triglyceride levels
Symptoms
Medical history
Sometimes genetic testing
Even without clear genetic test results, doctors can still recognise FCS by looking at symptoms, medical history, and triglyceride levels6,7
You’re not alone
You may have seen multiple healthcare professionals before receiving a diagnosis – a journey many people with FCS share6–8
Real stories from people living with FCS
Other people whose lives are impacted by FCS have shared their stories and experiences
Abbreviations
FCS, Familial Chylomicronaemia Syndrome; LPL, lipoprotein lipase.
Show References
- Action FCS. About FCS. Available at: https://www.actionfcs.org/about-fcs/. Last accessed May 2026.
- Falko JM, O’Connor CM, et al. Endocr Pract. 2018;24(8):756–763.
- Feingold KR, Grunfeld C, et al. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–.
- Davidson M, Stevenson M, et al. J Clin Lipidol. 2018;12(4):898–907.e2.
- Action FCS. Symptoms of FCS. Available at https://www.actionfcs.org/about-fcs/symptoms-of-fcs/. Last accessed May 2026.
- Larouche MB, Watts GFC, et al. Curr Opin Endocrinol Diabetes Obes. 2025;32(2):75–88.
- Moulin P, Dufour R, et al. Atherosclerosis. 2018;275:265–72.
- Stroes E, Moulin P, et al. Atheroscler Suppl. 2017;23:1–7.
- Virani SS, Morris PB, et al. J Am Coll Cardiol. 2021;78(9):960–93.