What is Sitosterolemia (Phytosterolemia)?
Sitosterolemia is a rare health issue that causes a buildup of plant-based substances, known as plant sterols, in the blood. It’s a condition that can be passed down in families and it usually starts showing symptoms in early childhood. The symptoms are similar to those of a condition called familial hypercholesterolemia, making it difficult for doctors to tell the difference. People with sitosterolemia absorb more plant sterols and similar substances known as stanols, than healthy individuals.
If not addressed, this absorption can lead to high cholesterol levels and subsequently early onset of atherosclerosis, a condition where artery walls thicken due to fat buildup. This condition can lead to severe heart issues like coronary artery disease and heart attacks, at an early age if left untreated.
As it’s not well recognized, thus often undiagnosed. Diagnosis is done by blood tests to measure the levels of plant sterols followed by genetic testing. However, once diagnosed, the condition can be managed with changes in eating habits and medication. Avoiding food that contains plant sterols along with taking medication, EZETIMIBE, significantly reduces these sterols level in the blood.
What Causes Sitosterolemia (Phytosterolemia)?
Sitosterolemia is a rare condition where the body absorbs too much plant sterols. Typically, a healthy person only absorbs a small amount of plant sterols they consume. Once these sterols enter cells in the digestive system, they are moved into the hollow section of the gut. Interestingly, this transport is facilitated by proteins known as ATP-binding cassette transporter (ABC transporter) proteins.
In someone with sitosterolemia though, this ABC transporter protein doesn’t work properly. Therefore, the plant sterols aren’t moved into the gut as they should be. Additionally, the liver isn’t able to get rid of sterols into the bile as effectively. So, the result is too much accumulation of plant sterols in the person’s blood.
The way sitosterolemia functions is due to a genetic mutation. The genes ABCG5 and ABCG8 are responsible for creating the ABC transporter proteins. To be more specific, they create sterolin-1 and sterolin-2. If there’s a mutation in either of these two genes, the ABC transporter might break down. This condition is a type of ‘autosomal recessive disorder’ – this means that the defective gene is passed down from both parents who may or may not show any symptoms of the disease.
Risk Factors and Frequency for Sitosterolemia (Phytosterolemia)
There have been over 100 cases of a certain disorder mentioned in global medical literature. However, it is believed to be often undiagnosed due to its similarities with other disorders related to body fat. Unfortunately, we don’t know the actual frequency of this disorder because testing isn’t done often. But it’s guessed that it could affect as many as 1 in every 50,000 people.
- Usually, symptoms show up early in life, and patients are generally diagnosed during the first twenty years of their lives.
- If the diagnosis is delayed, it’s possible that patients might not be diagnosed until they’ve had a heart problem.
- False negatives in testing could also happen, especially because of the frequent use of a medication called ezetimibe, which is used to treat fat disorders.
Signs and Symptoms of Sitosterolemia (Phytosterolemia)
Sitosterolemia is a condition that shares many similarities with other fat-related disorders. Patients often develop tendon xanthomas, which are also characteristic of a condition called familial hypercholesterolemia. Other signs may include corneal arcus and xanthelasma, though these are less frequent. People with sitosterolemia may also experience nonspecific symptoms like stomach pain and joint pain. Depending on how long they’ve had the disease, they may also have an enlarged spleen or liver. It’s also important for doctors to ask about the person’s diet to understand their intake of plant sterols.
- Tendon xanthomas (often)
- Corneal arcus (occasionally)
- Xanthelasma (occasionally)
- Stomach pain (nonspecific symptom)
- Joint pain (nonspecific symptom)
- Enlarged spleen or liver (depending on disease timeline)
- Dietary habits (to assess plant sterol intake)
Testing for Sitosterolemia (Phytosterolemia)
If your doctor suspects you have a cholesterol disorder called sitosterolemia, they will usually conduct a laboratory examination. Typical tests include checking your cholesterol levels, including low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglycerides. In sitosterolemia, total cholesterol might be high, but other values in this test don’t give specific details about the condition. Sitosterolemia patients usually don’t respond well to statins, a group of drugs used to lower cholesterol levels in the blood.
The standard way to diagnose sitosterolemia is to check the levels of plant sterols like sitosterol, campesterol, and stigmasterol in your blood. Patients with sitosterolemia often have plant sterol levels about 30 times higher than healthy individuals. For a healthy person, plant sterols usually make up less than one percent of their total cholesterol. If you have sitosterolemia, this number could range from 10 to 65 mg/dL depending on the severity of your condition. Be mindful that some situations can cause the test results to be inaccurate. For instance, taking specific medications like ezetimibe or bile acid-binding resin or eating a low plant sterol diet could make the test results falsely negative. On the other hand, conditions like cholestasis and consuming infant formulas containing plant sterols could make the test falsely positive. If your doctor suspects sitosterolemia based on your plant sterol levels, they might confirm this with genetic testing which–in case of sitosterolemia–often shows specific variations in the genes ABCG5 or ABCG8.
Some other common features of sitosterolemia include hemolytic anemia and thrombocytopenia, conditions affecting red blood cells and platelets in the blood respectively, which can be diagnosed by doing a Complete Blood Count (CBC) and other tests for hemolysis. Patients might also have liver disease or premature atherosclerosis, the build-up of plaques in your arteries that can lead to heart diseases, with an unknown cause. In such cases, more specialised tests like computed tomography (CT) of the heart, calcium scoring, and echocardiography (an ultrasound for your heart) might be conducted.
Treatment Options for Sitosterolemia (Phytosterolemia)
To treat sitosterolemia, a condition where you have too many plant sterols (substances found in certain foods) in your body, the first step is usually changing what you eat. You would need to eat fewer foods with a lot of plant sterols, like vegetable oils, nuts, and avocados. This diet change can lead to a noticeable drop in your plant sterol levels and cholesterol levels.
However, changes in diet alone are usually not enough to control sitosterolemia, so medications are often needed as well. One common medication is ezetimibe, which is approved by the Food and Drug Administration (FDA) in the United States for treating sitosterolemia. It works by blocking plant sterols from getting into your body, which can help lower your overall plant sterol levels. There are other medication options as well like cholestyramine, but it would be used in combination with ezetimibe, not on its own. Sometimes, a surgical procedure called an ileal bypass might be needed for severe cases.
Although you might think of statins (a type of drug that lowers cholesterol) being used to treat sitosterolemia because it also deals with cholesterol levels, they are not typically used here. They might be prescribed to help protect the heart and manage cholesterol levels in patients with sitosterolemia, but they can’t lower plant sterol levels. Therefore, statins alone aren’t enough to treat sitosterolemia. If a person with sitosterolemia is also dealing with heart disease, they would need to receive other standard treatments for heart disease in addition to managing their sitosterolemia.
What else can Sitosterolemia (Phytosterolemia) be?
When considering the diagnosis of a disease called Sitosterolemia, doctors often need to rule out other conditions which might have similar symptoms. Such conditions might include:
- Familial hypercholesterolemia – This shows signs similar to Sitosterolemia but exhibits very high LDL levels.
- Lecithin-cholesterol acyltransferase (LCAT) deficiency – This illness is featured by very low HDL, increased very-low-density lipoprotein (VLDL), and high levels of triglyceride.
- Tangier disease – In this condition, HDL levels are extremely low, something that is not observed in Sitosterolemia.
- Cerebrotendinous xanthomatosis
- Familial dysbetalipoproteinemia
- Familial hypertriglyceridemia
What to expect with Sitosterolemia (Phytosterolemia)
Sitosterolemia is a condition that, if not treated, can lead to early heart disease and death. Since this disease usually starts early in life, it’s crucial to receive a diagnosis in enough time to prevent the build-up of fatty deposits in the arteries (known as atherosclerosis). However, since sitosterolemia is quite rare, doctors aren’t yet sure about its long-term effects or outcome.
By learning more about this disorder, doctors hope to diagnose more people and gain a better understanding of what to expect in the future for those with the condition.
Possible Complications When Diagnosed with Sitosterolemia (Phytosterolemia)
Some potential health conditions associated with gallstones include:
- Heart diseases such as atherosclerosis and coronary artery disease
- Heart attack, known in medical terms as myocardial infarction
- Aortic stenosis, a condition in which the heart’s aortic valve narrows
- Premature death from heart-related problems
- Hemolytic anemia, a condition where red blood cells are destroyed faster than they’re made
- Thrombocytopenia, a low level of platelets in the blood
- Splenomegaly, or an enlarged spleen
- Liver disease and cirrhosis, where healthy liver tissue is replaced with scar tissue
- Arthritis and arthralgia, causing joint pain
Preventing Sitosterolemia (Phytosterolemia)
Managing sitosterolemia, a disease with abnormal cholesterol absorption, greatly depends on maintaining a specific diet. This involves limiting the intake of plant sterols, substances found in many plant-based foods. It’s crucial for patients to understand that consuming plant sterols can lead to serious health issues.
To help them adhere to a plant sterol-free diet, patients are often advised to consult with a nutrition expert. They can provide detailed guidelines about foods to avoid and recommend suitable alternatives.
Since sitosterolemia usually starts early in life, it can be a bit more difficult to deal with. This is why family members are often involved in patient education and counseling, ensuring they fully understand and support the dietary changes. It might be confusing because the foods that need to be avoided aren’t usually unhealthy, so it’s important to remember that these restrictions are specific to managing sitosterolemia.
