What is Sitosterolemia?
Sitosterolemia (also known as phytosterolemia) is a rare disease caused by the accumulation of dietary plant sterols in the body. Accumulation of plant sterols can lead to premature death if left untreated. Sitosterolemia is caused by mutations of the ABCG genes encoding for transporters of plant sterols out of the body.
What are a plant sterols/ stanols?
Plant sterols (also known as phytosterols) and stanols are substances found in plant based foods, similar to cholesterol in humans. Vegetable oils are a major source of plant sterols but they can also be found in nuts, cereals and legumes.
For many people, eating foods with added plant sterols can help lower LDL-cholesterol levels, a benefit for those persons who have high LDL-cholesterol levels, which is a well-known risk factor for heart disease. However, consuming plant sterols for someone with Sitosterolemia is harmful to their health.
There are many different plant sterols but some of the main ones are sitosterol, campesterol and stigmasterol.
What causes it?
Sitosterolemia is caused by a mutation or change in the ABCG8 and ABCG5 genes. These two genes code for proteins that pump plant sterols out of intestinal cells as well as liver cells. The mutations or changes in these genes lead to abnormal proteins that are unable to do their job correctly in the body. Therefore, high concentrations of plant sterols accumulate throughout the body.
Sitosterolemia is an inherited autosomal recessive genetic condition. Autosomal recessive is one of the ways a disease can be passed down through families. An autosomal recessive disease means that to develop the disease two copies of the abnormal gene must be present. Affected individuals inherit two copies of the mutated or changed 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.
Sitosterolemia has been found in the Amish, Hutterite, Japanese and Chinese ancestry as well as other populations.
Northern European/ white individuals more frequently have mutations in ABCG8 where Chinese, Japanese, and Indian tend to have mutations in ABCG5.
Tendon and tuberous xanthomas (build-up of yellowish cholesterol rich material over joints)
Hemolysis (destruction of red blood cells) and platelet abnormalities
Early coronary atherosclerosis due to plaque and fat build up
Some patients have high cholesterol with no family history of it
Every case is different and patient may only exhibit one or two of the symptoms, not necessarily all.