What is Sitosterolemia?
Sitosterolemia is a rare inherited disease characterized by storage of plant sterols. Affected individuals have abnormally high concentrations of plant sterols (phytosterols) in blood and various tissues due to hyper-absorption from the intestine and reduced excretion from the liver. The plant sterols include sitosterol, stigmasterol, and campesterol. Individuals with sitosterolemia also have moderate to high blood cholesterol concentrations since plant sterols and cholesterol are absorbed in the same way by the body. Plant sterols and cholesterol build up in the arteries and in tendons causing swellings (xanthomas) in individuals with sitosterolemia. Sitosterolemia is characterized by premature thickening of the artery walls due to plaque and fat build up. The build-up of plaque can lead to early heart disease. The full clinical spectrum of the disease is not known, but the commonly observed symptoms are listed below.
Common Symptoms Include:
- Tendon and tuberous xanthomas that occur in unusual locations –e.g. heels, knees, elbows, buttocks
- Hemolysis and platelet abnormalities (examples, hemolytic anemia, stomatocytes and macrothrombocytopenia)
- Premature coronary atherosclerosis
- Increased cholesterol concentration in a child without a family history of heart disease or elevated cholesterol
Who gets Sitosterolemia?
Sitosterolemia is a very rare disease. There have been approximately 80 patients worldwide diagnosed with Sitosterolemia. It can affect Individuals of all ages, ethnicities and sex.
What causes Sitosterolemia?
We normally consume plant sterols in our diet. These plant sterols enter the intestinal cells, but then are pumped back out into the gut for disposal to keep plant sterols out of the body. Sitosterolemia is caused by changes (mutations) in the ABCG8 and ABCG5 genes. These two genes code for proteins that normally pump plant sterols out of intestinal cells and liver cells. The changes in these genes result in abnormal proteins that are unable to do their job correctly. Therefore, high concentrations of plant sterols accumulate throughout the body.
Sitosterolemia is an inherited autosomal recessive genetic condition. Affected individuals inherit two copies of the mutated ABCG8 or ABCG5 genes, one from each parent. Therefore, the parents are "carriers" of Sitosterolemia, meaning that they have one normal functioning copy and one non-functioning copy of the genes. With each pregnancy, carriers of Sitosterolemia have a 1 in 4 or 25% chance of having a child with the disease.
How is Sitosterolemia diagnosed?
Sitosterolemia is diagnosed by measuring elevated plant sterols in the blood, including sitosterol, campesterol and stigmasterol. Normal cholesterol testing will not diagnose sitosterolemia because it cannot distinguish among the different sterols. DNA analysis of the ABCG5 and ABCG8 genes can be helpful detect mutations and confirm the diagnosis, but such testing is not routinely available.
What is/is there treatment for Sitosterolemia?
The primary goal is of treatment is to reduce the concentration of plant sterols in the blood (to be below 1 mg/dl, if possible). Sitosterolemia can be managed by restricting foods that are high in concentrations of plant sterols and shellfish sterols and by pharmacologic therapy. Foods with high plants sterols include vegetable oils, nuts, seeds and chocolate. The drug ezetimibe is effective in decreasing the plant sterol concentration in blood. Cholestryramine has been helpful for some individuals. There are some margarines and medications enriched with plant sterols or stanols (e.g. sitostanol and campestanol) that are often prescribed as a treatment for people with hypercholesterolemia; it is important for individuals with Sitosterolemia to avoid ingesting these preparations.