What is the role of hyperabsorption in the pathophysiology of sitosterolemia (phytosterolemia)?

Updated: May 24, 2019
  • Author: Robert D Steiner, MD; Chief Editor: Luis O Rohena, MD, MS, FAAP, FACMG  more...
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Answer

The intestinal pathway for cholesterol absorption is beginning to be elucidated. Mutations in the ABCG8 and ABCG5 genes were recently identified as the underlying cause of sitosterolemia. The active pumping back into the intestine of passively absorbed plant sterols is disrupted, and hepatic secretion of the resultant accumulation of these sterols is decreased. Animal studies have revealed that expression of G5 and G8 in either intestine or liver is sufficient to limit accumulation of plasma phytosterols in animal models of sitosterolemia, but expression in both tissues is required to maintain the very low levels observed in wild type animals. [9]

The ability of the liver to preferentially excrete plant sterols into the bile is apparently impaired. Although bile acid synthesis remains the same as in healthy people, the total excretion of sterols in the bile is reportedly less than 50% in subjects with sitosterolemia compared with control subjects. The mechanism for decreased hepatic secretion is unknown.


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