the molecular mechanisms regulating the amount of dietary cholesterol retained by the body, as well as the body's ability to exclude other dietary sterols selectively, are poorly understood. An average Western diet will contain approximately 250-500 mg of dietary cholesterol and approximately 200-400 mg of non-cholesterol sterols, of which plant sterols are the major constituents
approximately 50-60% of dietary cholesterol is absorbed and retained by the normal human body, but less than 1% of the non-cholesterol sterols are retained. There thus exists a subtle mechanism that allows the body to distinguish between cholesterol and non-cholesterol sterols
in sitosterolaemia (phytosterolaemia), a rare autosomal recessive disorder, affected individuals hyperabsorb and retain not only cholesterol but also all other sterols, including plant and shellfish sterols from the intestine
consequently, patients with this disease have very high levels of plant sterols in the plasma, and develop tendon and tuberous xanthomas, accelerated atherosclerosis, and premature coronary artery disease
the STSL locus has been mapped to human chromosome 2p21. Mutations in two tandem ABC genes, ABCG5 and ABCG8, encoding sterolin-1 and -2, respectively, are now known to be mutant in sitosterolemia
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