Sitosterolemia: exclusion of genes involved in reduced cholesterol biosynthesis.
Sitosterolemia (phytosterolemia) is a rare autosomal recessively inherited disorder that is characterized by premature coronary artery disease, xanthomas, and increased plasma plant sterols and 5alpha-stanols. Affected individuals show an increased absorption of both cholesterol and sitosterol from the diet, decreased bile clearance of these sterols and their metabolites resulting in markedly expanded whole body cholesterol and sitosterol pools. Biochemical studies have shown that the regulation of the cholesterol biosynthetic pathway may be abnormal in this condition. In particular, the activities and mRNA for the biosynthetic enzymes, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and HMG-CoA synthase are low in liver biopsy specimens isolated from affected individuals, suggesting replete intracellular cholesterol pools. However, the membrane expression of hepatocyte low density lipoprotein receptors was increased, suggesting discordant regulation. Segregation analyses in three families for the genes for HMG-CoA reductase, HMG-CoA synthase, and LDL-receptor excluded these as sites of mutation. In view of the previously described discordant regulation of the above genes in sitosterolemia, the two major regulatory genes for this pathway, sterol regulatory element binding proteins (SREBP-1 and -2), were also examined. These genes did not segregate with the disease and were thus excluded. Two other genes involved in cholesterol absorption and chylomicron secretion, namely acyl coenzyme A:cholesterol acyltransferase (ACAT) and microsomal triglyceride transfer protein (MTP) were also examined for segregation and similarly excluded. Although the gene defect in sitosterolemia therefore remains to be elucidated, important candidate genes have been excluded.
Patel
S B
SB
Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas 75235-9052, USA.
Honda
A
A
Salen
G
G
D000328:Adult; D022762:CCAAT-Enhancer-Binding Proteins; D002784:Cholesterol / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D006904:Hydroxymethylglutaryl-CoA Synthase / Q000378:metabolism; D008052:Lipid Metabolism, Inborn Errors / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010375:Pedigree; D011973:Receptors, LDL / Q000378:metabolism; D012855:Sitosterols / Q000097:blood*; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011973:Receptors, LDL; C497387:SREBF1 protein, human; D012855:Sitosterols; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D006904:Hydroxymethylglutaryl-CoA Synthase