Sitosterolemia (phytosterolaemia) is a rare inherited metabolic disease. Only 45 cases have been described so far. However, the percentage of patients may be much higher, as it is likely that some patients with hyperlipidaemia are misdiagnosed.
Sitosterolemia( phytosterolemia ) is an autosomal recessive disease. The mutation concerns genes encoding ABC family protein transporters (ABCG8 and ABCG5 located in the 2p21 locus). Mammalian cells do not use plant sterols - normally plant sterols are poorly absorbed from the gastrointestinal tract - less than 5% is absorbed.Sterols passively pass into intestinal cells and then most of them are pumped back into the intestinal lumen by the ABC protein transporter (ATP-Binding Cassette). Transporters. In patients with sitosterolaemia, pumping through the ABC transporter is disturbed. The liver's ability to excrete plant sterols into the bile is markedly reduced. On the other hand, the synthesis of bile acids occurs as in he althy people. The excretion of sterols in the bile is lower by 50% compared to the control group. The mechanism of the decreased hepatic secretion is unknown. In patients there is a decrease in cholesterol synthesis: associated with the inhibition of hepatic and intestinal synthesis, and a decrease in HMG-CoA reductase (an enzyme that controls cholesterol biosynthesis). It is debatable whether this is due to the accumulation of sterols in the body. Recent data indicate that secondary effects of unknown regulators may lead to decreased HMG-CoA reductase activity in this disease. This goes hand in hand with significantly increased expression of LDL receptors.
Sitosterolemia: symptoms
Sitosterolemia has several features in common with familial hypercholesterolaemia (FH), such as the presence of tendon jaundice in the first 10 years of life and the premature development of atherosclerosis. Additionally, the following may be present:
- reduced range of motion in joints
- redness
- itching
- excessive heat associated with inflammation
Jaundice can also occur subcutaneously on the buttocks of children. It should be remembered that not every patient has tendon yellows, so their absence does not preclude a diagnosis. Lipid degeneration of the cornea and yellow tufts on the eyelids occurless often. Unlike FH, patients with sitosterelomy have normal or moderately elevated total cholesterol and very high levels of plant sterols (sitosterol, campesterol, stigmasterol, avenosterol) and 5a-stanols. Coronary heart disease and its associated he alth consequences are a major problem and cause of premature death. patients with sitosterolaemia.
Sitosterolemia: diagnosis
The disease is confirmed by basic laboratory tests: hematological and liver enzymes.
Sitosterolemia: treatment
The basis of treatment is to reduce the consumption of food products rich in plant sterols (including vegetable oils, olives and avocados). As plant sterols are found in all plant-derived food products, dietary treatment is not sufficient to control the disease. Statins are used, which in addition to lowering cholesterol levels and a positive effect on atherosclerotic disease, lower the level of plant sterols themselves. Bile acid binding resins (e.g. cholestyramine, colestipol) may be considered. In October 2002, a new cholesterol absorption inhibitor, ezetimibe, was introduced to treat sitosterolaemia. This drug is the standard of care as it blocks sterol absorption and can be used in conjunction with bile acid resins. Before the appearance of esimibe, in some cases, a bypass was performed in the ileum to lower the level of sterols in the body. The effectiveness of therapy should be regularly monitored by measuring the level of sterols in the body.