Phytosterolaemia: Causes, Symptoms and Treatment
Phytosterolaemia is a rare inherited metabolic disorder in which plant sterols accumulate in the blood and tissues, significantly increasing the risk of cardiovascular disease.
Things worth knowing about "Phytosterolaemia"
Phytosterolaemia is a rare inherited metabolic disorder in which plant sterols accumulate in the blood and tissues, significantly increasing the risk of cardiovascular disease.
What is Phytosterolaemia?
Phytosterolaemia (also known as sitosterolaemia) is a rare, inherited metabolic disorder. In this condition, plant-derived sterols – known as phytosterols, including sitosterol, campesterol, and stigmasterol – are excessively absorbed from the intestine and insufficiently excreted through bile. This leads to abnormal accumulation of these substances in the blood and various body tissues.
Phytosterols are naturally found in plant-based foods such as nuts, seeds, vegetable oils, and vegetables. In healthy individuals, very little of these compounds is absorbed. In patients with phytosterolaemia, a genetic defect disrupts this regulatory mechanism, causing blood levels to rise significantly.
Causes
The condition is caused by mutations in the ABCG5 or ABCG8 genes. These genes encode transporter proteins located in the intestine and liver that are responsible for excreting phytosterols and cholesterol back into the intestinal lumen. When this function is impaired, plant sterols accumulate throughout the body.
- The disease follows an autosomal recessive inheritance pattern, meaning both parents must pass on a defective gene copy for a child to be affected.
- The condition is extremely rare worldwide, estimated to affect fewer than 1 in 200,000 individuals.
- Higher prevalence has been observed in certain populations where consanguineous marriages are more common.
Symptoms
The symptoms of phytosterolaemia are varied and can differ significantly in severity from person to person:
- Xanthomas: Yellowish fatty deposits in the skin, tendons (particularly the Achilles tendon and extensor tendons of the hands), and eyelids (xanthelasmas), caused by sterol accumulation in connective tissue.
- Premature atherosclerosis: Deposition of phytosterols in artery walls leads to early vascular calcification and narrowing, significantly increasing the risk of heart attack and stroke.
- Haemolytic anaemia: Destruction of red blood cells, leading to fatigue, pallor, and weakness.
- Thrombocytopaenia: Reduced platelet count, which can cause an increased tendency to bleed.
- Joint and muscle pain may also occur.
- In children, growth retardation can be observed.
Diagnosis
Phytosterolaemia is often diagnosed late because it is very rare and its symptoms can resemble those of other lipid disorders.
- Blood tests: Measurement of plasma phytosterol levels (e.g., sitosterol, campesterol). Elevated values are indicative of the diagnosis.
- Lipid profile: Total cholesterol may be elevated, normal, or even reduced, which can make diagnosis more challenging.
- Genetic testing: Confirmation by identifying mutations in the ABCG5 or ABCG8 genes.
- Family screening: Since the disorder is hereditary, siblings and parents should also be tested.
Treatment
Treatment of phytosterolaemia aims to reduce phytosterol levels in the blood and prevent long-term complications.
Dietary Modification
A low-phytosterol diet is the cornerstone of management. Affected individuals should reduce their intake of foods high in phytosterols, including:
- Vegetable oils (e.g., rapeseed, sunflower, and olive oil)
- Nuts and seeds
- Wholegrain products
- Legumes
- Phytosterol-enriched foods (e.g., certain margarines or yoghurt products)
Pharmacological Therapy
- Ezetimibe: This medication inhibits the intestinal absorption of cholesterol and phytosterols and is the treatment of choice in phytosterolaemia. It effectively lowers plasma phytosterol concentrations.
- Bile acid sequestrants (colestyramine): Bind bile acids in the intestine and can promote sterol excretion, although they are used less frequently today.
- Statins are less effective in phytosterolaemia than in other lipid disorders and may even be contraindicated in some patients.
Regular Monitoring
Regular medical monitoring of phytosterol levels, blood lipid values, and cardiological assessments are essential for the early detection and management of complications.
References
- Berge K. E. et al. - Accumulation of dietary cholesterol in sitosterolemia caused by mutations in adjacent ABC transporters. Science, 2000; 290(5497): 1771–1775.
- Patel S. B. - Sitosterolemia: insights and challenges. Current Opinion in Lipidology, 2014; 25(3): 185–191.
- Salen G., Shefer S., Nguyen L. et al. - Sitosterolemia. Journal of Lipid Research, 1992; 33(7): 945–955.
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