Sitosterolemia

A rare genetic disorder affecting cholesterol metabolism

Sitosterolemia, also known as phytosterolemia, is a rare autosomal recessive genetic disorder characterized by the accumulation of dietary plant sterols in the blood and tissues. This condition is caused by mutations in the ABCG5 or ABCG8 genes, which are responsible for regulating the absorption and excretion of sterols.

Pathophysiology

Diagram of autosomal recessive inheritance

Sitosterolemia is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene, one from each parent, to manifest the disease. The ABCG5 and ABCG8 genes encode proteins that form a transporter complex in the enterocytes of the small intestine and in the liver. This complex is responsible for limiting the absorption of dietary sterols and promoting their excretion into the bile.

In individuals with sitosterolemia, mutations in these genes lead to defective transporter function, resulting in increased absorption and decreased excretion of plant sterols, such as sitosterol, campesterol, and stigmasterol. This accumulation of sterols can lead to the formation of xanthomas, premature atherosclerosis, and other complications.

Clinical Features

Patients with sitosterolemia may present with a variety of symptoms, including:

• Xanthomas: These are cholesterol-rich deposits that can appear on the skin, particularly on the elbows, knees, and buttocks.
• Atherosclerosis: The accumulation of sterols can lead to the premature development of atherosclerosis, increasing the risk of cardiovascular disease.
• Hematological abnormalities: Some patients may experience hemolytic anemia and thrombocytopenia.
• Arthralgia: Joint pain may occur due to the deposition of sterols in the joints.

Diagnosis

The diagnosis of sitosterolemia is based on clinical evaluation, laboratory testing, and genetic analysis. Laboratory tests typically reveal elevated levels of plant sterols in the blood. Genetic testing can confirm mutations in the ABCG5 or ABCG8 genes.

Management

Management of sitosterolemia involves dietary modifications and pharmacological interventions. Patients are advised to follow a diet low in plant sterols, which includes avoiding foods high in nuts, seeds, and vegetable oils.

Pharmacological treatment may include the use of ezetimibe, a medication that inhibits the absorption of sterols in the intestine. In some cases, bile acid sequestrants may also be used to reduce sterol levels.

Prognosis

With appropriate management, individuals with sitosterolemia can lead relatively normal lives. However, without treatment, the risk of cardiovascular complications and other health issues increases significantly.

Related pages

• Hyperlipidemia
• Cholesterol
• Genetic disorders