Sitosterolemia: Causes, Symptoms & Treatment
Sitosterolemia is a rare inherited metabolic disorder in which plant sterols (phytosterols) accumulate in the blood and tissues, significantly increasing the risk of cardiovascular disease.
Things worth knowing about "Sitosterolemia"
Sitosterolemia is a rare inherited metabolic disorder in which plant sterols (phytosterols) accumulate in the blood and tissues, significantly increasing the risk of cardiovascular disease.
What is Sitosterolemia?
Sitosterolemia (also known as phytosterolemia) is a rare, autosomal recessive inherited metabolic disorder. Affected individuals are unable to adequately excrete plant-derived sterols – so-called phytosterols such as sitosterol, campesterol, and stigmasterol – from the body. As a result, these substances accumulate in the blood and various tissues, leading to serious health complications.
Causes
The disorder is caused by mutations in the genes ABCG5 or ABCG8. These genes encode transporter proteins that normally return plant sterols from the intestine back into the intestinal lumen or excrete them via bile. When these transporters are defective, phytosterols are absorbed in excessive amounts from food and stored in the body.
- Autosomal recessive inheritance (both parents must carry the defective gene)
- Mutations in ABCG5 or ABCG8 on chromosome 2p21
- Increased intestinal absorption of phytosterols
- Reduced biliary excretion of phytosterols
Symptoms
The clinical signs of sitosterolemia can vary widely and are often recognized late. Typical symptoms include:
- Xanthomas: Deposits of sterols in the skin, particularly on tendons and knees
- Premature atherosclerosis: Hardening and narrowing of the arteries, which can lead to heart attack or stroke
- Elevated blood cholesterol levels (not always present)
- Hemolytic anemia (impaired breakdown of red blood cells)
- Macrothrombocytopenia (enlarged, reduced platelets)
- Joint pain and arthropathy
- In severe cases: cardiovascular events already in childhood
Diagnosis
Diagnosis of sitosterolemia requires specific testing, as standard blood tests often fail to detect the condition:
- Plasma sterol analysis: Measurement of phytosterol concentrations (sitosterol, campesterol) in the blood using gas chromatography or mass spectrometry
- Genetic testing: Detection of mutations in ABCG5 or ABCG8
- General lipid profile (cholesterol, LDL, HDL, triglycerides)
- Blood count to rule out hemolytic anemia
Because the condition is very rare, it is frequently misdiagnosed for years, for example as familial hypercholesterolemia.
Treatment
Treatment of sitosterolemia aims to reduce phytosterol concentrations in the blood and prevent cardiovascular complications:
Dietary Measures
A phytosterol-restricted diet is the cornerstone of therapy. Affected individuals should avoid foods with high phytosterol content, including:
- Plant-based oils (e.g., rapeseed oil, soybean oil)
- Nuts and seeds
- Foods enriched with phytosterols (e.g., certain margarine products)
- Legumes in large quantities
Drug Therapy
- Ezetimibe: Inhibits intestinal absorption of sterols via the NPC1L1 transporter and is the first-line treatment of choice
- Cholestyramine (bile acid sequestrant): Binds bile acids in the intestine, thereby reducing sterol absorption
- Statins show only limited benefit in sitosterolemia
Follow-up Monitoring
Regular monitoring of plasma phytosterol levels as well as cardiovascular examinations are essential to assess treatment success and detect complications early.
References
- Berge KE et al. – Accumulation of dietary cholesterol in sitosterolemia caused by mutations in adjacent ABC transporters. Science, 2000; 290(5497): 1771–1775.
- Patel SB – Plant sterols and stanols: Their role in health and disease. Journal of Clinical Lipidology, 2008; 2(2): S11–S19.
- European Association for the Study of the Liver (EASL) – Clinical Practice Guidelines on lipid-related disorders, 2022. Available at: www.easl.eu
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