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Sitosterolemia (Phytosterolemia)

Rare Autosomal Recessive Sterol Storage Disease with Premature Atherosclerosis

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

References (5)

This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Endokrinoloji department. Book Appointment →

What is Sitosterolemia (Phytosterolemia)?

Sitosterolemia (phytosterolemia) is an autosomal recessive sterol storage disease with prevalence approximately 1 in 200,000 to 1 in 1,000,000 worldwide.

Caused by loss-of-function mutations in ABCG5 or ABCG8 genes encoding heterodimeric ATP-binding cassette transporters that normally limit intestinal sterol absorption and promote biliary excretion of plant sterols.

Pathophysiology involves marked increase in intestinal absorption of dietary plant sterols (normally <5%, increasing to 20–40%) and decreased biliary excretion, leading to plasma plant sterol elevation 30- to 100-fold above normal.

Often misdiagnosed as familial hypercholesterolemia due to xanthomas and premature atherosclerosis but distinguished by markedly elevated plant sterols on specialized assays.

Symptoms

Tendinous and tuberous xanthomas in childhood or adolescence (Achilles tendon, knees, elbows, hands), often the presenting feature
Premature atherosclerotic cardiovascular disease (myocardial infarction, stroke) sometimes in second to fourth decades despite only modestly elevated total cholesterol
Hemolytic anemia with stomatocytes and macrothrombocytopenia (large platelets), often misdiagnosed as Mediterranean stomatocytosis or hereditary hemolytic anemia
Splenomegaly from hemolysis
Abnormal liver enzymes and rarely hepatic steatosis or cirrhosis
Joint manifestations: pseudo-arthritis from xanthomatous tendon involvement
Family history of premature atherosclerosis or unexplained xanthomas in young persons

Risk Factors

Autosomal recessive inheritance: parental consanguinity increases risk
Compound heterozygotes with one mutant ABCG5 or ABCG8 allele have intermediate elevations of plant sterols and may have moderately increased cardiovascular risk
Higher prevalence in Old Order Amish, Japanese, and certain founder populations
Differential considerations: familial hypercholesterolemia, cerebrotendinous xanthomatosis (CTX), familial defective ApoB, autosomal dominant or recessive hypercholesterolemia
Increased plant sterol intake (vegan diet, plant sterol-supplemented foods or margarines) markedly worsens disease and is contraindicated

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Tendinous xanthomas in child or adolescent, especially with normal or mildly elevated cholesterol
  • Premature coronary artery disease in young adult without traditional risk factors
  • Unexplained hemolytic anemia with stomatocytes and macrothrombocytopenia
  • Family history suggestive of recessive sterol storage disease
  • Established sitosterolemia with progressive cardiovascular disease, persistent xanthomas, or hematologic deterioration despite therapy

Treatment Methods

01
Diagnostic confirmation: plasma plant sterol measurement (sitosterol typically >10 mg/dL, normal <0.5 mg/dL) by gas chromatography-mass spectrometry; campesterol and stigmasterol also markedly elevated
02
Genetic testing for ABCG5 and ABCG8 sequence variants confirms diagnosis and enables family screening
03
Differentiation from familial hypercholesterolemia: total cholesterol may be normal or mildly elevated; LDL receptor pathway intact; statins are far less effective
04
Dietary management: strict avoidance of plant sterol-rich foods (vegetable oils, nuts, seeds, plant sterol-fortified margarines and yogurts); low-fat diet; reduce shellfish (rich in stigmasterol); referral to specialized lipid dietitian
05
Ezetimibe 10 mg/day: cornerstone of medical therapy by inhibiting intestinal Niemann-Pick C1-Like 1 (NPC1L1) protein, reduces plant sterols by 50% and induces xanthoma regression
06
Bile acid sequestrants (cholestyramine 8–24 g/day, colesevelam 3.75–4.375 g/day, colestipol): bind plant sterols in gut and prevent enterohepatic recirculation, often combined with ezetimibe for additive effect
07
Statins: relatively ineffective for plant sterol reduction but may be added for residual cardiovascular risk and modest LDL lowering
08
Splenectomy: rarely indicated for severe symptomatic hemolysis if medical therapy insufficient (controversial; preferred medical control)
09
Cardiovascular risk assessment: lipid profile (including plant sterols), coronary calcium scoring, carotid ultrasound, stress testing in symptomatic adults
10
Surveillance: serial plant sterol levels every 3–6 months, xanthoma documentation, hemoglobin and platelet counts, transaminases, liver imaging if hepatomegaly; cardiovascular evaluation periodically
11
Family screening: genetic counseling and cascade testing of first-degree relatives; identified carriers receive dietary advice and lipid monitoring

Which Department to Visit?

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