G-->A substitution at position -75 of the apolipoprotein A-I gene promoter. Evidence against a direct effect on HDL cholesterol levels

Single nucleotide polymorphisms of APOA1 gene and their relationship with serum apolipoprotein A-I concentrations in the native population of Assam

Background

There is a growing interest in the role of allelic variants of the APOA1 gene in relation to a number of disorders. We described two common polymorphisms of the APOA1 gene, G-75A and C+83T and investigated their potential influence on the serum apolipoprotein A-I (apo A-I) levels in the native population of Assam — a region that is ethnically distinct and from where no information is hitherto available.

Methods

Blood samples were collected from 150 healthy volunteers. Apo A-I levels were estimated by immunoturbidometry. Genotyping was done by a PCR-RFLP method that involved DNA extraction from whole blood, followed by polymerase chain reaction and digestion of the PCR product by MspI restriction enzyme, and analysis of fragment sizes in 12% polyacrylamide gel.

Results

The GG variant at G-75A locus and CC variant at C+83T locus were the most prevalent. GG/CC was the most common combination. Homozygous TT genotype was not detected in any of the subjects. The rare allele frequencies for the G-75A and C+83T sites were found to be 0.22 and 0.06 respectively, which significantly differed from those reported in some other populations in neighbouring regions. Serum apo A-I concentrations did not vary significantly across the detected genotypes. These findings were consistent in both sexes.

Conclusion

We described the distribution of the G-75A and C+83T polymorphisms of the APOA1 gene in the population of Assam for the first time. These polymorphisms were not found to directly influence apo A-I concentrations in this population either individually or synergistically.

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The G-75A and C + 83T polymorphisms of the APOA1 gene are described for the first time in the native population of Assam, north-east India.

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The minor allelic frequencies of G-75A and C + 83T differ significantly from some populations in the adjoining regions.

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The G-75A and C + 83T polymorphisms do not influence the serum apolipoprotein A-I levels in the current population.

Re-sequencing of the APOAI promoter region and the genetic association of the -75G > A polymorphism with increased cholesterol and low density lipoprotein levels among a sample of the Kuwaiti population

Background

APOAI, a member of the APOAI/CIII/IV/V gene cluster on chromosome 11q23-24, encodes a major protein component of HDL that has been associated with serum lipid levels. The aim of this study was to determine the genetic association of polymorphisms in the APOAI promoter region with plasma lipid levels in a cohort of healthy Kuwaiti volunteers.

Methods

A 435 bp region of the APOAI promoter was analyzed by re-sequencing in 549 Kuwaiti samples. DNA was extracted from blood taken from 549 healthy Kuwaiti volunteers who had fasted for the previous 12 h. Univariate and multivariate analysis was used to determine allele association with serum lipid levels.

Results

The target sequence included a partial segment of the promoter region, 5’UTR and exon 1 located between nucleotides −141 to +294 upstream of the APOAI gene on chromosome 11. No novel single nucleotide polymorphisms (SNPs) were observed. The sequences obtained were deposited with the NCBI GenBank with accession number [GenBank: JX438706]. The allelic frequencies for the three SNPs were as follows: APOAI rs670G = 0.807; rs5069C = 0.964; rs1799837G = 0.997 and found to be in HWE. A significant association (p < 0.05) was observed for the APOAI rs670 polymorphism with increased serum LDL-C. Multivariate analysis showed that APOAI rs670 was an independent predictive factor when controlling for age, sex and BMI for both LDL-C (OR: 1.66, p = 0.014) and TC (OR: 1.77, p = 0.006) levels.

Conclusion

This study is the first to report sequence analysis of the APOAI promoter in an Arab population. The unexpected positive association found between the APOAI rs670 polymorphism and increased levels of LDL-C and TC may be due to linkage disequilibrium with other polymorphisms in candidate and neighboring genes known to be associated with lipid metabolism and transport.

Can novel Apo A-I polymorphisms be responsible for low HDL in South Asian immigrants?

Coronary artery disease (CAD) is the leading cause of death in the world. Even though its rates have decreased worldwide over the past 30 years, event rates are still high in South Asians. South Asians are known to have low high-density lipoprotein (HDL) levels. The objective of this study was to identify Apolipoprotein A-I (Apo A-I) polymorphisms, the main protein component of HDL and explore its association with low HDL levels in South Asians. A pilot study on 30 South Asians was conducted and 12-h fasting samples for C-reactive protein, total cholesterol, HDL, low-density lipoprotein (LDL), triglycerides, Lipoprotein (a), Insulin, glucose levels, DNA extraction, and sequencing of Apo A-I gene were done. DNA sequencing revealed six novel Apo A-I single nucleotide polymorphisms (SNPs) in South Asians, one of which (rs 35293760, C938T) was significantly associated with low (<40 mg/dl) HDL levels (P = 0.004). The association was also seen with total cholesterol (P = 0.026) and LDL levels (P = 0.032). This pilot work has highlighted some of the gene-environment associations that could be responsible for low HDL and may be excess CAD in South Asians. Further larger studies are required to explore and uncover these associations that could be responsible for excess CAD risk in South Asians.

The common apolipoprotein A-1 polymorphism -75A>G is associated with ethnic differences in recurrent coronary events after recovery from an acute myocardial infarction

Since data regarding the relationship between a common polymorphism (SNP) of the apoA1 gene with apoA1 levels and risk of coronary artery disease are inconsistent, we hypothesized that its association with recurrent coronary events differs for White and Black individuals with diagnosed coronary heart disease. The apoA1 -75G>A SNP was genotyped in a cohort of 834 Black (n=129) and White (n=705) post-myocardial infarction patients. Recurrent coronary events (coronary-related death, non-fatal myocardial infarction, or unstable angina) were documented during an average follow-up of 28 months. Thirty percent of White and 21% of Black patients carried the SNP. Cox proportional-hazards regression analysis, adjusting for clinical and laboratory covariates, demonstrated that the SNP was not associated with recurrent events in the total cohort (HR=1.37, 95% CI 0.95-1.97; p= 0.09) but was the only variable associated with an increased risk of recurrent cardiac events in Blacks (HR=2.40, 95% CI 1.07-5.40; p= 0.034). Conversely in Whites, the SNP was not associated with recurrent events (HR=1.12, 95% CI 0.75-1.67; p= 0.59) whereas apoB (HR=1.78, 95% CI 1.20 -2.65; p= 0.0042) and calcium channel blocker use (HR=2.53, 95% CI 1.72-3.72; p<0.001) were associated; p= 0.0024 for interaction between ethnicity and the SNP. A common apoA1 SNP is associated with a significantly increased risk of recurrent cardiac events among Black, but not White, postmyocardial infarction patients. Relationships with lipoproteins may help explain this finding.

Synergistic effect between apolipoprotein E and apolipoprotein A1 gene polymorphisms in the risk for coronary artery disease

Alterations in lipid metabolism and genetic predisposition are major risk factors for coronary artery disease (CAD). Variations in genes involved in lipid metabolism may act synergistically to confer risk or protection against CAD. The objective of the present study was to determine such interactions in variants of apolipoprotein E and apolipoprotein A1 genes. One hundred and forty subjects with clinically confirmed CAD and 100 unrelated normal subjects participated in the study. Multiple regression analysis was used to relate lipid and apolipoprotein profiles with genotypes. Odd ratios were calculated for various combinations of ApoE and ApoA1 genotypes. Prevalence of ApoE 'E4' and ApoA1 'A' and 'T' alleles was significantly higher in patients than controls. Serum apolipoprotein E and apolipoprotein A1 levels were significantly lower in CAD patients than controls. When lipid parameters were related to genotypes, the polymorphisms associated to various markers were in agreement with previous reports. ApoE 2/4 genotype in combination with either ApoA1 heterozygous GA or CT genotype conferred higher risk of CAD. E3 allele in homozygous or heterozygous state in combination with ApoA1+83 CC genotype conferred highest protection (P < 0.05). Thus, it appears that ApoE and ApoA1 gene variants may act synergistically to associate with risk and protection against CAD.

ApolipoproteinA1-75 G/A (M1-) polymorphism and lipoprotein(a); anti- vs. pro-Atherogenic properties

BACKGROUND

ApolipoproteinA1 (apoA1) is the major apoprotein constituent of high-density-lipoprotein(HDL). The relationship of apoA1 -75 bp(M1-) allele polymorphism with lipoprotein phenotype and cardiovascular disease (CVD) remain unclear. Overnight fasting blood samples were collected from a cohort of high-risk Omani population, 90 non-diabetic subjects and 149 type 2 diabetes mellitus (T2DM) subjects for genotype and phenotype studies.

RESULTS

The M1+ and M1- alleles frequencies were 0.808 and 0.192 for M1+ and M1-, respectively, comparable to the frequency of apoA1 (M1+ and M1-) amongst a healthy Omani population, 0.788 and 0.212, respectively. The frequencies of the hetero- and homozygous subjects for the MspI polymorphism at -75 (M1-) of the apoA1 gene were in Hardy-Weinberg equilibrium. The mean Lp(a) concentration was significantly higher(P = 0.02) in subjects carrying M1- allele compared to M1+ allele of the APOA1 gene with an odd ratio of 2.3(95% CI, 1.13-14.3), irrespective of gender and the diabetic status.

CONCLUSION

ApolipoproteinA1-75 G/A (M1-) polymorphism is relatively common and is positively associated with Lp(a) and therefore, may confer a potential risk for cardiovascular disease (CVD).

Genetic interactions with diet influence the risk of cardiovascular disease

Single-nucleotide polymorphisms are an integral component of the evolutionary process that over millennia have resulted from the interaction between the environment and the human genome. Relatively recent changes in diet have upset this interaction with respect to the nutritional environment, but nutritional science is beginning to better understand the interaction between genes and diet, with the resulting potential to influence cardiovascular disease risk by dietary modification. Single-nucleotide polymorphisms in several genes have been linked to differential effects in terms of lipid metabolism; however, even a simple model of benefit and risk is difficult to interpret in terms of dietary advice to carriers of the various alleles because of conflicting interactions between different genes. The n-3 family of polyunsaturated fatty acids is underrepresented in our modern diet; much of the benefit of polyunsaturated fatty acids found in studies of various polymorphisms seems to be linked to increased n-3 polyunsaturated fatty acid intake. The nascent science of nutrigenomics faces many challenges; more and better research is needed to clarify the picture, rebut scepticism, and re-invigorate the discussion concerning genetic polymorphism and its interaction with diet.

Genome-wide linkage analyses and candidate gene fine mapping for HDL3 cholesterol: the Framingham Study

High density lipoprotein cholesterol (HDL-C) is inversely associated with coronary heart disease and has a genetic component; however, linkage to HDL-C is not conclusive. Subfractions of HDL, such as HDL(3)-C, may be better phenotypes for linkage studies. Using HDL(3)-C levels measured on 907 Framingham Heart Study subjects from 330 families around 1987, we conducted a genome-wide variance components linkage analysis with 401 microsatellite markers spaced approximately 10 centimorgan (cM) apart. Nine candidate genes were identified and annotated using a bioinformatics approach in the region of the highest linkage peak. Twenty-eight single nucleotide polymorphisms (SNPs) were selected from these candidate genes, and linkage and family-based association fine mapping were conducted using these SNPs. The highest multipoint log-of-the-odds (LOD) score from the initial linkage analysis was 3.7 at 133 cM on chromosome 6. Linkage analyses with additional SNPs yielded the highest LOD score of 4.0 at 129 cM on chromosome 6. Family-based association analysis revealed that SNP rs2257104 in PLAGL1 at approximately 143 cM was associated with multivariable adjusted HDL(3) (P = 0.03). Further study of the linkage region and exploration of other variants in PLAGL1 are warranted to define the potential functional variants of HDL-C metabolism.

APOA1 polymorphisms are associated with variations in serum triglyceride concentrations in hypercholesterolemic individuals

Background: Apolipoprotein A-I gene (

Methods:

Results: G–75A polymorphism was associated with differences in serum concentrations of triglyceride and very low-density lipoprotein (VLDL)-cholesterol (p=0.026) in HC men. After atorvastatin treatment, women carrying the

Conclusion: Our data suggest that

The interactive effects of hepatic lipase gene promoter polymorphisms with sex and obesity on high-density-lipoprotein cholesterol levels in Taiwanese–Chinese

OBJECTIVES

Hepatic lipase (HL) is involved in the metabolism of several lipoproteins and plays a key role in reverse cholesterol transport. The aim of the current study was to test the statistical association between two HL gene promoter polymorphisms (HL-514C/T and HL-250G/A) and lipoprotein profiles in a Taiwanese-Chinese population.

METHODS

A sample population of 716 Taiwanese-Chinese individuals was analyzed. DNA was extracted from the blood and genotypes were determined by polymerase chain reaction, restriction enzyme digestion, and agarose gel electrophoresis.

RESULTS

Analysis of the data revealed that these two polymorphisms are in strong linkage disequilibrium (D/D(max)=0.97, P<0.001). A significantly lower total cholesterol/HDL-C ratio was noted for carriers with the -514T and -250A alleles compared to non-carriers (P=0.007 and 0.004, respectively). A significant trend of the association was also found on the high levels of high-density-lipoprotein cholesterol (HDL-C) among carriers with the -514T and -250A alleles as opposed to that of non-carriers (P=0.030 and 0.023, respectively). Multivariate analysis has demonstrated that the effects of HL-514C/T and HL-250G/A polymorphisms on HDL-C levels were not affected by subjects' sex, body mass index, plasma triglyceride levels and the cholesterol ester transfer protein gene TaqIB polymorphism. Subgroup analysis on each sex has revealed that the two studied polymorphisms were significantly associated with HDL-C levels among males but not significant in women. The same association between obese and non-obese men was not consistent. The P-value of the respective polymorphisms on HDL-C levels were 0.012 and 0.002 among obese men, but not significant among non-obese men.

CONCLUSION

Analysis of our data revealed an independent association between the HL gene promoter polymorphisms and HDL-C levels in Taiwanese-Chinese. The data also suggests that the HL-514C/T and HL-250G/A polymorphisms interact with sex and obesity on HDL-C levels. The findings give clues for identifying high risk population in preventive medicine and clinical diagnosis. The subsequent impacts on treatment profiles and prognosis were derived from this study.

Consistency of genetic inheritance mode and heritability patterns of triglyceride vs. high density lipoprotein cholesterol ratio in two Taiwanese family samples

BACKGROUND

Triglyceride/HDL cholesterol ratio (TG/HDL-C) is considered as a risk factor for cardiovascular events. Genetic components were important in controlling the variation in western countries. But the mode of inheritance and family aggregation patterns were still unknown among Asian-Pacific countries. This study, based on families recruited from community and hospital, is aimed to investigate the mode of inheritance, heritability and shared environmental factors in controlling TG/HDL-C.

RESULTS

Two populations, one from community-based families (n = 988, 894 parent-offspring and 453 sibling pairs) and the other from hospital-based families (n = 1313, 76 parent-offspring and 52 sibling pairs) were sampled. The population in hospital-based families had higher mean age values than community-based families (54.7 vs. 34.0). Logarithmic transformed TG/ HDL-C values, after adjusted by age, gender and body mass index, were for genetic analyses. Significant parent-offspring and sibling correlations were also found in both samples. The parent-offspring correlation coefficient was higher in the hospital-based families than in the community-based families. Genetic heritability was higher in community-based families (0.338 +/- 0.114, p = 0.002), but the common shared environmental factor was higher in hospital-based families (0.203 +/- 0.042, p < 0.001). Commingling analyses showed that more than one-component distribution models were the best-fit models to explain the variance in both populations. Complex segregation analysis by regressive models revealed that in both samples the best-fit model of TG/HDL-C was the model of environmental effects plus familial correlation, in which significant parent-offspring and sibling correlations were demonstrated. Models of major gene effects were rejected in both samples.

CONCLUSION

Variations of TG/HDL-C in the normal ranges were likely to be influenced by multiple factors, including environmental and genetic components. Higher genetic factors were proved in younger community-based families than in older hospital-based families.

The apo A-I gene promoter region polymorphism determines the severity of hyperlipidemia after heart transplantation

BACKGROUND

To study whether the Apolipoprotein A-I (apo A-I) promoter region gene polymorphism produces changes in the lipid profile of heart transplant recipients.

METHODS

One hundred and three heart transplant recipients (93 men and 10 women, with a mean age of 47 +/- 13 yr) receiving triple immunosuppressive therapy were submitted to a genetic study of the apo A-I gene promoter region. Anthropometric and analytical data, including lipid profile, arterial blood pressure, were collected prior to transplantation and 3, 6, 12, and 24 months after transplantation.

RESULTS

Sixty-three subjects had the GG genotype and 40 the GA genotype. Carriers of the GA genotype had higher triglyceride levels at 6 months and 2 yr (2.50 +/- 1.20 versus 1.93 +/- 0.98 mmol/L and 2.46 +/- 1.58 versus 1.60 +/- 0.68 mmol/L, respectively, p < 0.001), and a greater rise in LDL-cholesterol at 1 yr than the GG subjects (4.57 +/- 1.16 versus 4.16 +/- 1.18 mmol/L, p < 0.05). Multiple regression analyses showed that genetic variants at the apo A-I promoter region are responsible for 11% of the variability in triglyceride levels at 6 months (p = 0.005).

CONCLUSIONS

The GA genotype of the apo A-I promoter region produces a greater rise in plasma triglyceride and LDL-cholesterol levels in heart transplant patients.

Significance of a polymorphism (G-->A transition) in the -75 position of the apolipoprotein A-I gene promoter on serum high density lipoprotein-cholesterol levels in Japanese hyperlipidemic subjects

High density lipoprotein-cholesterol (HDL-C) levels are inversely related to the incidence of coronary artery disease. We studied the influence of a G(-75)-->A transition in the promoter of the apolipoprotein (apo) A-I gene, a major protein component of HDL, on serum HDL-C levels in hyperlipidemic subjects. Seventy three hyperlipidemic subjects with serum levels of high HDL-C (HDL-C > or = 70 mg/dl, Group H) were compared with hyperlipidemic subjects with levels of HDL-C between 40 and 70 mg/dl (Group N) and those with HDL-C < 40 mg/dl (Group L). Group H showed a higher incidence (45.2%) of low plasma cholesteryl ester transfer protein (CETP) activity than Groups N (9.1%) and L (5.3%) (p < 0.001). Group H had a higher incidence of the G(-75)-->A transition (0.275) than Groups N (0.117, p < 0.05) and L (0.056, p < 0.01), among subjects with normal CETP activities. The HDL-C levels in subjects with the transition (84 +/- 16 mg/dl) were higher than those in subjects without the transition (56 +/- 12 mg/dl) (p < 0.05). These data suggest that a G(-75)-->A transition of the apo A-I gene promoter, in addition to the common mutation of CETP gene, contributes to high HDL-C levels among hyperlipidemic patients in Japan.

Effects of apolipoprotein A-I genetic variations on plasma apolipoprotein, serum lipoprotein and glucose levels

The present authors investigated the individual and combined associations of the apolipoprotein (apo) A-I -75 bp and +83 bp polymorphisms with plasma lipid, lipoprotein and apolipoprotein levels in 734 Caucasian men and women. The frequency of the A allele at position -75 bp (G-->A) was 0.14 in women and 0.17 in men. The frequencies for the rare M2 allele at position +83 bp and/or 84 bp (C-->T and G-->A, respectively) were 0.04 and 0.05 in women and men, respectively. In women, the A allele was associated with significantly higher levels of apo B (P = 0.016), total cholesterol (TC) (P = 0.005), low-density lipoprotein cholesterol (LDL-C) (P = 0.018) and TC:high-density lipoprotein (HDL) ratio (P = 0.026) compared to the G/G subjects. In men, no significant associations were detected between the -75 bp polymorphism and any lipid trait examined. The M2 allele for the +83 bp polymorphism was significantly associated in men with higher levels of apo A-I (P = 0.002) and TC (P = 0.046). In women, a significant effect was observed for TC (P = 0.036), with M2+/- subjects having lower levels than M2+/+ subjects. Significant linkage disequilibrium (P = 0.037) between the apo A-I -75 bp and +83 bp polymorphisms was detected. Women carrying both rare alleles (G/A M2+/-) had significantly higher TC:HDL ratios (P = 0.031) compared to the other haplotypes. In men, significant differences were observed for apo A-I (P = 0.021) and TC (P = 0.044), with carriers of the G/G M2+/- haplotype having the highest values compared to other genotype combinations. In conclusion, the -75 bp (G/A) polymorphism appears to have a significant effect on levels of apo B, plasma TC and LDL-C in women, while the +83 bp polymorphism seems to affect the apo A-I levels in men, and the plasma cholesterol levels in both genders.

Polyunsaturated fatty acids modulate the effects of the APOA1 G-A polymorphism on HDL-cholesterol concentrations in a sex-specific manner: the Framingham Study

BACKGROUND

A common G-to-A substitution in the promoter area (-75 base pairs) of the apolipoprotein A-I gene (APOA1) has been described. The A allele was shown to be associated with higher HDL-cholesterol concentrations in some studies but not in others.

OBJECTIVE

We examined whether dietary fat modulates the association between this polymorphism and HDL-cholesterol concentrations.

DESIGN

We studied a population-based sample of 755 men and 822 women from the Framingham Offspring Study.

RESULTS

The frequency of the A allele was 0.165. No significant differences were observed between G/G subjects and carriers of the A allele for any lipid variables. In multivariate linear regression models, HDL-cholesterol concentrations in women were associated with a significant interaction between polyunsaturated fatty acid (PUFA) intake as a continuous variable and APOA1 genotype (P = 0.005). By using 3 categories of PUFA intake, we found a significantly different effect of APOA1 genotype across PUFA categories in women. When PUFA intake was <4% of energy, G/G subjects had approximately 14% higher HDL-cholesterol concentrations than did carriers of the A allele (P < 0.05). Conversely, when PUFA intake was >8%, HDL-cholesterol concentrations in carriers of the A allele were 13% higher than those of G/G subjects (P < 0.05). No significant allelic difference was observed for subjects in the range of PUFA intake of 4-8% of energy. These interactions were not significant in men.

CONCLUSIONS

We found a significant gene-diet interaction associated with the APOA1 G-A polymorphism. In women carriers of the A allele, higher PUFA intakes were associated with higher HDL-cholesterol concentrations, whereas the opposite effect was observed in G/G women.

Variations in the promoter region of the apolipoprotein A-1 gene influence plasma lipoprotein(a) levels in Asian Indian neonates from Singapore

We studied the influence of two DNA polymorphisms (-75 bp G/A and +83 bp C/T) in the promoter region of the apolipoprotein A-1 (apoA1) gene on cord plasma level of lipoprotein(a) [Lp(a)] in 1076 newborns of both genders from the three major ethnic groups in Singapore-Chinese, Malays, and Asian Indians. The frequency of the A: allele at -75 bp in the Indians was significantly lower than the Chinese and Malays. There was no linkage disequilibrium between the two sites studied. Both polymorphic sites were not significantly associated with any lipid factors except for Lp(a) levels in the Asian Indians. The AA and CC homozygotes were significantly associated with lower Lp(a) levels. These associations were specific only to the male Indian neonates. The genetic variations at the -75 and +83 bp explained 6.9% and 7.2%, respectively, of the total variability of plasma Lp(a) levels at birth in the Asian Indians. The Lp(a) levels were also significantly different between composite genotypes in the order GG/TT > GA/CT > GG/CT > GA/CC > GG/CC > AA/CC. The effects of the two polymorphisms seem to be additive as the composite genotypes were able to explain 14% of the Lp(a) variance, equivalent to the sum of the two constituent sites. Our results showed that there is significant ethnic- and gender-specific influence of the apoA1 gene on plasma Lp(a) levels at birth that is inherent and independent of known gene-environment interactions.

Molecular mechanisms, lipoprotein abnormalities and atherogenicity of hyperalphalipoproteinemia

Hyperalphalipoproteinemia (HALP) is caused by a variety of genetic and environmental factors. Among these, plasma cholesteryl ester transfer protein (CETP) deficiency is the most important and frequent cause of HALP in the Asian populations. CETP facilitates the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to apolipoprotein (apo) B-containing lipoproteins, and is a key protein in the reverse cholesterol transport system. The deficiency of CETP causes various abnormalities in the concentration, composition, and function of both HDL and low density lipoprotein (LDL). The significance of CETP in terms of atherosclerosis had been controversial. However, the in vitro evidence showed large CE-rich HDL particles in CETP deficiency are defective in cholesterol efflux. Similarly, scavenger receptor BI (SR-BI) knockout mice show a marked increase in HDL-cholesterol but accelerated atherosclerosis in atherosclerosis-susceptible mice. Recent epidemiological studies in Japanese-Americans and in Omagari area where HALP subjects with the intron 14 splicing defect of CETP gene are markedly frequent, have demonstrated an increased incidence of coronary atherosclerosis in CETP-deficient patients. Thus, CETP deficiency is a state of impaired reverse cholesterol transport which may possibly lead to the development of atherosclerosis. The current review will focus on the molecular mechanisms and atherogenicity of HALP, especially CETP deficiency.

Genetic association of five apolipoprotein polymorphisms with serum lipoprotein-lipid levels in African blacks

Genetic studies carried out mainly in European and European-derived populations have shown that common polymorphisms in genes coding for apolipoproteins are significant determinants of serum lipoprotein-lipid levels variation. However, except for a few sporadic studies, the distribution of apolipoprotein polymorphisms and their association with serum lipoprotein-lipid levels have not been evaluated systematically in African or African-derived populations. In this investigation we have studied five apolipoprotein polymorphisms, including APOA1/MspI-75 bp, APOA1/MspI+83 bp, APOC3/PvuII, APOE, and APOH in 786 Africans (493 men, 293 women) from Nigeria. The sample is comprised of Nigerian civil servants consisting of 462 junior staff (less affluent) and 324 senior staff (more affluent) where staff status is a correlate of their socioeconomic status. We first examined genetic associations in the total sample stratified by gender to determine the role of apolipoprotein polymorphisms in affecting serum lipid profile in the general population, and then by staff status to evaluate possible gene-environment interactions. In the total sample, the APOC3/PvuII polymorphism showed significant effect on HDL-cholesterol (P = 0.029) and HDL3-cholesterol (P = 0.009) in women, and the APOE polymorphism was significantly associated with total cholesterol (P = 0.031) and LDL-cholesterol (P = 0.0006) in women. Multiple regression analyses showed that the APOC3/PvuII polymorphism accounts for about 2 and 3% of the variation in HDL-cholesterol and HDL3-cholesterol, respectively, in women; while the APOE polymorphism accounted for about 5 and 6% of the variation in total- and LDL-cholesterol, respectively, in women. Whereas the association of the APOE polymorphism was independent of the staff status, the significant affect of the APOC3/PvuII polymorphism on HDL- and HDL3-cholesterol was confined to senior staff women where it explained about 7% of their variation. We also observed an interaction between staff and the APOH polymorphism in affecting cholesterol levels. The APOH polymorphism showed significant association with total cholesterol (P = 0.010) and LDL-cholesterol (P = 0.016) in senior staff women and explained about 7 and 5% of their phenotypic variations, respectively. These data indicate that gene-environment interaction may play an important role in affecting serum lipid profile in African populations.

Human pedigree-based quantitative-trait-locus mapping: localization of two genes influencing HDL-cholesterol metabolism

Common disorders with genetic susceptibilities involve the action of multiple genes interacting with each other and with environmental factors, making it difficult to localize the specific genetic loci responsible. An important route to the disentangling of this complex inheritance is through the study of normal physiological variation in quantitative risk factors that may underlie liability to disease. We present an analysis of HDL-cholesterol (HDL-C), which is inversely correlated with risk of heart disease. A variety of HDL subphenotypes were analyzed, including HDL particle-size classes and the concentrations and proportions of esterified and unesterified HDL-C. Results of a complete genomic screen in large, randomly ascertained pedigrees implicated two loci, one on chromosome 8 and the other on chromosome 15, that influence a component of HDL-C-namely, unesterified HDL2a-C. Multivariate analyses of multiple HDL phenotypes and simultaneous multilocus analysis of the quantitative-trait loci identified permit further characterization of the genetic effects on HDL-C. These analyses suggest that the action of the chromosome 8 locus is specific to unesterified cholesterol levels, whereas the chromosome 15 locus appears to influence both HDL-C concentration and distribution of cholesterol among HDL particle sizes.

The genetics of serum lipid responsiveness to dietary interventions

CHD is a multifactorial disease that is associated with non-modifiable risk factors, such as age, gender and genetic background, and with modifiable risk factors, including elevated total cholesterol and LDL-cholesterol levels. Lifestyle modification should be the primary treatment for lowering cholesterol values. The modifications recommended include dietary changes, regular aerobic exercise, and normalization of body weight. The recommended dietary changes include restriction in the amount of total fat, saturated fat and cholesterol together with an increase in the consumption of complex carbohydrate and dietary fibre, especially water-soluble fibre. However, nutrition scientists continue to question the value of these universal concepts and the public health benefits of low-fat diets, and an intense debate has been conducted in the literature on whether to focus on reduction of total fat or to aim efforts primarily towards reducing the consumption of saturated and trans fats. Moreover, it is well known that there is a striking variability between subjects in the response of serum cholesterol to diet. Multiple studies have examined the gene-diet interactions in the response of plasma lipid concentrations to changes in dietary fat and/or cholesterol. These studies have focused on candidate genes known to play key roles in lipoprotein metabolism. Among the gene loci examined, APOE has been the most studied, and the current evidence suggests that this locus might be responsible for some of the inter-individual variability in dietary response. Other loci, including APOA4, APOA1, APOB, APOC3, LPL and CETP have also been found to account for some of the variability in the fasting and fed states.

The effect on transcription efficiency of the apolipoprotein AI gene of DNA variants at the 5' untranslated region

Elevated circulating levels of high-density lipoprotein and apolipoprotein AI are associated with reduced coronary artery disease risk. We have shown that a C to T substitution at +83 bp and a G to A substitution at -75 bp of the apolipoprotein AI gene are both related to increased high-density lipoprotein levels in a healthy population but not in a coronary population, among whom the same mutations are associated with increased disease severity. In the present study, we explored the effects of these base changes on transcriptional efficiency in vitro. We directionally cloned (using polymerase chain reaction) the 5' region of the apolipoprotein AI gene (-281 to +330 bp) with GC, GT, and AC haplotypes into a pGL3-luciferase reporter gene basic vector, and transfected the constructed vectors into HepG2 cells. The cells carrying the T allele at the +83 bp site (GT 112.3 +/- 12.4) had the same transcriptional efficiency as those bearing the C allele (GC 126.3 +/- 9.6). However, for cells with the A allele at -75 bp there was a twofold decrease in transcription (AC 63.1 +/- 9.3) accompanied by similar changes in Luc+ mRNA levels; this reduced transcription was only present if the apolipoprotein AI leader sequence was included in the insert. While the findings are inconsistent with the T or A allele being associated with higher high-density lipoprotein levels, they are consistent with the finding that the alleles are associated with an increased coronary artery disease risk, and demonstrate that the 5' leader region of the apolipoprotein AI gene participates in regulating apolipoprotein AI transcription. They also suggest that other regions of the apolipoprotein AI gene may have an active role in such regulation, and that environmental effects may influence allele-specific expression.

Influence of genetic variation at the apo A-I gene locus on lipid levels and response to diet in familial hypercholesterolemia

We have examined the apo AI - 75 (G/A) and apo AI + 83(MspI +/-) polymorphisms at the APOA1 gene locus for associations with plasma lipid levels and response to an NCEP-I diet in 69 (44 women, 25 men) heterozygotes for familial hypercholesterolemia (FH). Subjects were studied at baseline (after consuming for one month a diet with 35%, fat, 10% saturated, and 300 mg/day cholesterol) and after 3 months of an NCEP-I diet. No gender-related differences for any of the lipid variables examined were found and the data were analyzed for men and women combined. For the apo AI - 75 (G/A) polymorphism, there were 51 G/G and 18 G/A subjects. At baseline, G/A subjects showed significantly lower total cholesterol (p = 0.0036), and LDL-C (p = 0.0023), and apo B (p = 0.0209), than G/G individuals, but no differences were found for HDL-C, triglycerides and VLDL-C values. Following the NCEP-I diet these genotype-related differences remained significant for total and LDL-C. The MspI (-) allele at the apo AI + 83 polymorphism was detected in the heterozygous state in five subjects and its presence was not associated with altered baseline lipids nor with dietary response to the NCEP-I diet. Our results suggest that FH subjects carrying the A allele at the apoAI - 75 (G/A) polymorphism have significantly lower total and LDL-C and apo B baseline levels but respond to a low-fat diet with similar reductions in total and LDL-C when compared with homozygotes for the G allele at this polymorphic site.

Human apolipoprotein A-I gene promoter mutation influences plasma low density lipoprotein cholesterol response to dietary fat saturation

Previous studies have shown that the A to G transition occurring at position -75 bp upstream of the transcriptional start site in the human apolipoprotein A-I gene may affect plasma high density lipoprotein cholesterol (HDL-C) levels and low density lipoprotein cholesterol (LDL-C) response to changes in amount of dietary fat. We have examined the response to dietary fat saturation as a function of this mutation in 50 men and women. Subjects were first fed a saturated (SAT) fat diet (35% fat, 17% SAT) for 28 days, followed by a diet rich in monounsaturated fatty (MUFA) acids (35% fat, 22% MUFA) for 35 days and a diet rich in polyunsaturated (PUFA) fat (35% fat, 13% PUFA) for 35 days. All meals were prepared and consumed at the study sites. Lipoproteins were measured at the end of each diet period. The allele frequency for the A allele was 0.13. Subjects carrying the A allele had higher plasma cholesterol, LDL-C and triglyceride levels than those homozygotes for the G allele. As compared to the SAT diet, a PUFA diet induced significantly greater plasma total (P = 0.003) and LDL-C decreases (P = 0.001) in G/A women (-1.62 and -1.32 mmol/l, respectively) than in G/G subjects (-0.87 and -0.74 mmol/l for plasma and LDL-C, respectively). Multiple regression analysis demonstrated that in women, the variability in LDL-C response from a diet rich in SAT fat to a diet rich in PUFA was primarily due to LDL-C levels (during the SAT phase), accounting for 55.1% of the variance, waist to hip ratio (W/H; 11.4%) and the G/A polymorphism (10%). Whereas in men the major determinant of this response was smoking (21.4%). In conclusion, the G/A polymorphism appears to have a small but significant effect on plasma LDL-C responsiveness to changes in dietary fat saturation specially in women.

Small genetic effects in complex diseases: a review of regulatory sequence variants in dyslipoproteinemia and atherosclerosis

OBJECTIVE

Most reported mutations that affect lipoprotein metabolism are found within the coding sequences of genes. Recently, a few mutations that occur within promoter sequences have been detected. These promoter sequence variants are the topic of the present review.

METHODS

Some of these variants are fairly common genomic variants in the promoter regions for candidate genes in lipoprotein metabolism, such as APOA1, APOC3, LPA, and LPL. It is possible that such regulatory sequence variants can result in chronic, modestly altered levels of expression of qualitatively normal gene products. This might have a cumulative effect on quantitative phenotypes, such as plasma lipoprotein concentrations, over the long term. Such an effect might not be detected by existing clinical, biochemical, and/or physiological assays.

RESULTS

At present, the most consistent evidence from several lines of experiments indicates that genomic variation in the APOC3 promoter creates slightly elevated plasma triglyceride concentrations within the physiologic range. This altered expression appears to predispose to hypertriglyceridemia in the presence of secondary factors. Genetic variants that produce small effects on promoter function might thus be one component of the predisposition to complex diseases.

CONCLUSION

The aggregate of many small effects may create or contribute to a background of susceptibility that, under appropriate conditions, leads to development of frank dyslipidemia and atherosclerosis.

The genetic basis of atherosclerosis

Atherogenesis is a complex process that involves the contributions of several pathophysiological sub-systems. The dissection of the genetic component of atherosclerosis has become possible using current molecular technologies and analytical methods. Genetic factors are considered to determine the limits under which atherosclerosis develops and environmental factors are considered to position an individual's risk within these limits. Atherosclerosis proceeds through a well-characterized series of pathological stages that involve key cell types and the expression of particular gene products. Reductionist experimental models have helped to produce a list of several hundred candidate genes for the study of the genetic component of atherosclerosis. Within certain families and isolated communities the effect of a single candidate gene upon atherosclerosis susceptibility may be profound, as in the case of mutations in the gene encoding the low-density lipoprotein receptor, which produce familial hypercholesterolemia and premature atherosclerosis. However, particular candidate genes have small effects on atherosclerosis or to one of its intermediate phenotypes, in whole populations. In addition, pleiotropy and epistasis can confound the identification of the genetic component of atherosclerosis. Despite these limitations, it might still be possible to use genetic information clinically in order to classify individuals who are susceptible to atherosclerosis, especially if as yet undiscovered candidate genes are found to be important determinants of disease. However, it will be impossible to predict the onset of a clinical manifestation of atherosclerosis in a particular person. This is due to the confounding influence of other forces, such as variations in interindividual environmental landscape, non-linear interactions between genes and environment, and even the possible influence of biological chaos.

Haplotype analysis of two APOA1/MspI polymorphisms in relation to plasma levels of apo A-I and HDL-cholesterol

A common MspI polymorphism (G/A) in the promoter region of the APOA1 gene (-75 bp) has been shown to be associated with plasma apo A-I and HDL-C variation in several, but not all, studies. Recently another MspI polymorphic site (+/-) in the 5'region of APOA1 (+83 bp) has been identified which may also be relevant to HDL metabolism. This study was undertaken to elucidate the individual and combined effects of these two polymorphisms on plasma apo A-I and HDL-C levels in a cohort of 534 normoglycemic US Whites from the San Luis Valley, Colorado. Both polymorphisms were in strong linkage disequilibrium (P < 0.005); of the expected four haplotypes (G+, G-, A+, A-) the A- was not observed in this sample. Single site RFLP analysis revealed an independent and significant effect associated with each polymorphism on plasma apo A-I variation but not on HDL-C variation. Further analyses showed that the genotype effects of both polymorphisms were confined to non-smokers only. Haplotype analysis, combining both RFLPs, was more informative as this explained almost twice the amount of phenotypic variation in plasma apo A-I compared to single RFLP analysis in non-smokers. Compared to the most common haplotype (G+), the A+ and G- haplotypes were associated with increased plasma apo A-I levels by 6.7 mg/dl and 22.0 mg/dl, respectively in non-smoking men, and by 4.6 mg/dl and 15.1 mg/dl in non-smoking women, respectively. These data indicate that haplotype analysis in this region may be important to elucidate the functional significance of the APOA1 gene in HDL metabolism.