The microsomal triglyceride transfer protein gene-493T variant lowers cholesterol but increases the risk of coronary heart disease.
BACKGROUND
The microsomal triglyceride transfer protein (MTP) transfers lipids into apolipoprotein B-containing lipoproteins for secretion from liver, intestine, and heart. The T-variant of a functional polymorphism in the MTP promoter, MTP-493G/T, has been associated with reduced low-density lipoprotein cholesterol concentrations. We hypothesize that this polymorphism impacts on coronary heart disease (CHD) risk.


RESULTS
The effect of the polymorphism was therefore tested in the West of Scotland Coronary Prevention Study biobank (580 cases and 1160 controls). MTP-493T carrier status was associated with significantly increased risk of CHD despite a small reduction in total cholesterol. Compared with the genotypic group with the lowest event rate (MTP-493GG, pravastatin treatment), the respective odds ratios (95% confidence interval) in the placebo group for CHD events were: GG, 1.23 (0.92 to 1.63); GT, 1.53 (1.12 to 2.08); and TT, 2.78 (1.53 to 5.05), suggestive of a gene-dose effect. The excess risk for CHD of the MTP-493T-variant was eliminated by pravastatin treatment. The Uppsala Longitudinal Study of Adult Men (ULSAM), which is a 20-year follow-up study of CHD, was used as an independent confirmatory database. These unexpected findings prompted the investigation of non-plasma lipid factors that could associate the MTP gene with CHD risk. In a limited number of subjects (n=18), heart muscle biopsies showed a MTP-493T genotype-specific depression of MTP mRNA expression.


CONCLUSIONS
The MTP-493T variant confers an increased risk of CHD that is unrelated to plasma lipids and lipoproteins, but eliminated by pravastatin treatment. A direct effect of the MTP polymorphism on myocardial lipid metabolism and vulnerability upon ischemic damage cannot be excluded.
Ledmyr
Helena
H
King Gustaf V Research Institute, Karolinska Hospital, Stockholm, Sweden.
McMahon
Alex D
AD
Ehrenborg
Ewa
E
Nielsen
Lars B
LB
Neville
Matt
M
Lithell
Hans
H
MacFarlane
Peter W
PW
Packard
Christopher J
CJ
Karpe
Fredrik
F
D000012:Abetalipoproteinemia; D000924:Anticholesteremic Agents / Q000627:therapeutic use; D001706:Biopsy; D002352:Carrier Proteins / Q000235:genetics*; D016022:Case-Control Studies; D008078:Cholesterol, LDL / Q000172:deficiency; D003062:Codon / Q000235:genetics; D015331:Cohort Studies; D003327:Coronary Disease / Q000097:blood / Q000453:epidemiology* / Q000235:genetics; D004198:Disease Susceptibility; D004311:Double-Blind Method; D005838:Genotype; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000627:therapeutic use; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000453:epidemiology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D011110:Polymorphism, Genetic; D017035:Pravastatin / Q000627:therapeutic use; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011446:Prospective Studies; D012333:RNA, Messenger / Q000096:biosynthesis; D012306:Risk; D012606:Scotland / Q000453:epidemiology; D013548:Sweden / Q000453:epidemiology
D000924:Anticholesteremic Agents; D002352:Carrier Proteins; D008078:Cholesterol, LDL; D003062:Codon; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008074:Lipoproteins; D012333:RNA, Messenger; C106092:microsomal triglyceride transfer protein; D017035:Pravastatin