A low frequency variant within the GWAS locus of MTNR1B affects fasting glucose concentrations: genetic risk is modulated by obesity.

Two common variants (rs1387153, rs10830963) in MTNR1B have been reported to have independent effects on fasting blood glucose (FBG) levels with increased risk to type 2 diabetes (T2D) in recent genome-wide association studies (GWAS). In this investigation, we report the association of these two variants, and an additional variant (rs1374645) within the GWAS locus of MTNR1B with FBG, 2h glucose, insulin resistance (HOMA IR), ß-cell function (HOMA B), and T2D in our sample of Asian Sikhs from India. Our cohort comprised 2222 subjects [1201 T2D, 1021 controls]. None of these SNPs was associated with T2D in this cohort. Our data also could not confirm association of rs1387153 and rs10830963 with FBG phenotype. However, upon stratifying data according to body mass index (BMI) (low ≤ 25 kg/m(2) and high > 25 kg/m(2)) in normoglycemic subjects (n = 1021), the rs1374645 revealed a strong association with low FBG levels in low BMI group (ß = -0.073, p = 0.002, Bonferroni p = 0.01) compared to the high BMI group (ß = 0.015, p = 0.50). We also detected a strong evidence of interaction between rs1374645 and BMI with respect to FBG levels (p = 0.002). Our data provide new information about the significant impact of another MTNR1B variant on FBG levels that appears to be modulated by BMI. Future confirmation on independent datasets and functional studies will be required to define the role of this variant in fasting glucose variation.

Association of genetic variation in FTO with risk of obesity and type 2 diabetes with data from 96,551 East and South Asians.

AIMS/HYPOTHESIS: FTO harbours the strongest known obesity-susceptibility locus in Europeans. While there is growing evidence for a role for FTO in obesity risk in Asians, its association with type 2 diabetes, independently of BMI, remains inconsistent. To test whether there is an association of the FTO locus with obesity and type 2 diabetes, we conducted a meta-analysis of 32 populations including 96,551 East and South Asians. METHODS: All studies published on the association between FTO-rs9939609 (or proxy [r (2) > 0.98]) and BMI, obesity or type 2 diabetes in East or South Asians were invited. Each study group analysed their data according to a standardised analysis plan. Association with type 2 diabetes was also adjusted for BMI. Random-effects meta-analyses were performed to pool all effect sizes. RESULTS: The FTO-rs9939609 minor allele increased risk of obesity by 1.25-fold/allele (p = 9.0 × 10(-19)), overweight by 1.13-fold/allele (p = 1.0 × 10(-11)) and type 2 diabetes by 1.15-fold/allele (p = 5.5 × 10(-8)). The association with type 2 diabetes was attenuated after adjustment for BMI (OR 1.10-fold/allele, p = 6.6 × 10(-5)). The FTO-rs9939609 minor allele increased BMI by 0.26 kg/m(2) per allele (p = 2.8 × 10(-17)), WHR by 0.003/allele (p = 1.2 × 10(-6)), and body fat percentage by 0.31%/allele (p = 0.0005). Associations were similar using dominant models. While the minor allele is less common in East Asians (12-20%) than South Asians (30-33%), the effect of FTO variation on obesity-related traits and type 2 diabetes was similar in the two populations. CONCLUSIONS/INTERPRETATION: FTO is associated with increased risk of obesity and type 2 diabetes, with effect sizes similar in East and South Asians and similar to those observed in Europeans. Furthermore, FTO is also associated with type 2 diabetes independently of BMI.

An FTO variant is associated with Type 2 diabetes in South Asian populations after accounting for body mass index and waist circumference.

AIMS: A common variant, rs9939609, in the FTO (fat mass and obesity) gene is associated with adiposity in Europeans, explaining its relationship with diabetes. However, data are inconsistent in South Asians. Our aim was to investigate the association of the FTO rs9939609 variant with obesity, obesity-related traits and Type 2 diabetes in South Asian individuals, and to use meta-analyses to attempt to clarify to what extent BMI influences the association of FTO variants with diabetes in South Asians. METHODS: We analysed rs9939609 in two studies of Pakistani individuals: 1666 adults aged ≥40 years from the Karachi population-based Control of Blood Pressure and Risk Attenuation (COBRA) study and 2745 individuals of Punjabi ancestry who were part of a Type 2 diabetes case-control study (UK Asian Diabetes Study/Diabetes Genetics in Pakistan; UKADS/DGP). The main outcomes were BMI, waist circumference and diabetes. Regression analyses were performed to determine associations between FTO alleles and outcomes. Summary estimates were combined in a meta-analysis of 8091 South Asian individuals (3919 patients with Type 2 diabetes and 4172 control subjects), including those from two previous studies. RESULTS: In the 4411 Pakistani individuals from this study, the age-, sex- and diabetes-adjusted association of FTO variant rs9939609 with BMI was 0.45 (95%CI 0.24-0.67) kg/m(2) per A-allele (P=3.0 × 10(-5) ) and with waist circumference was 0.88 (95% CI 0.36-1.41) cm per A-allele (P=0.001). The A-allele (30% frequency) was also significantly associated with Type 2 diabetes [per A-allele odds ratio (95%CI) 1.18 (1.07-1.30); P=0.0009]. A meta-analysis of four South Asian studies with 8091 subjects showed that the FTO A-allele predisposes to Type 2 diabetes [1.22 (95%CI 1.14-1.31); P=1.07 × 10(-8) ] even after adjusting for BMI [1.18 (95%CI 1.10-1.27); P=1.02 × 10(-5) ] or waist circumference [1.18 (95%CI 1.10-1.27); P=3.97 × 10(-5) ]. CONCLUSIONS: The strong association between FTO genotype and BMI and waist circumference in South Asians is similar to that observed in Europeans. In contrast, the strong association of FTO genotype with diabetes is only partly accounted for by BMI.

TCF7L2 polymorphisms are associated with type 2 diabetes in Khatri Sikhs from North India: genetic variation affects lipid levels.

Recently, the transcription factor-7-like 2 (TCF7L2) gene has been identified as the most important type 2 diabetes mellitus (T2DM) susceptibility gene. Common intronic polymorphisms in this gene have been found to be strongly associated with T2DM susceptibility showing marked reproducibility in multiple populations. The purpose of this study was to confirm the reported association of six TCF7L2 variants in a Khatri Sikh diabetic sample from North India. We genotyped six-associated SNPs in a case-control sample consisting of 556 T2DM cases and 537 controls. We also examined the impact of these variants on body mass index (BMI), waist to hip ratio (WHR), fasting insulin, and glucose and lipid levels. We report replication of association of four of the six SNPs with T2DM in this Khatri Sikh sample [rs7903146, (p = 0.010); rs11196205, (p = 0.011); rs10885409, (p = 0.002) and rs4918789, (p = 0.029)], under a dominant model conferring odds ratios (ORs) of 1.39, 1.44, 1.57 and 1.36, respectively. Haplotype analysis provided further evidence of association by showing a significant difference between cases and controls as revealed by the global omnibus test (chi(2)= 19.36; p = 0.0036). Multiple linear regression analysis also revealed the risk allele carriers of three of four significant SNPs (rs7903146, rs11196205, rs10885409) to be significantly associated with increased fasting total cholesterol (p value = 0.019, 0.025, 0.006) and LDL cholesterol levels (p value = 0.021, 0.018, 0.005), respectively. Our findings confirm that the TCF7L2 gene is a major risk factor for development of T2DM in Khatri Sikhs. It also provides new information about the significant impact of TCF7L2 gene variants on plasma cholesterol levels that appear to be independent of BMI.

Chimpanzee apolipoprotein H (beta2-glycoprotein I): report on the gene structure, a common polymorphism, and a high prevalence of antiphospholipid antibodies.

Apolipoprotein H (apoH, protein; APOH, gene) is a 50-kDa glycoprotein that binds to negatively charged substrates, including phospholipids. ApoH is a main target antigen for the binding of antiphospholipid antibodies that are associated with thrombotic events. We have previously characterized the structural organization of the human APOH gene. Because of the significant structural homology between the human and chimpanzee genomes, we have employed oligonucleotides from the human APOH gene sequence to amplify chimpanzee DNA covering the entire transcribed region together with flanking sequence in the 5' region. As in humans, the chimpanzee APOH gene consists of eight exons and seven introns and encodes for a 326-amino-acid protein. The deduced amino acid and nucleotide sequence show 99.4% and 99.6% similarity between human and chimpanzee APOH, respectively. Using isoelectric focusing (IEF) and immunoblotting, we screened 155 chimpanzees (128 unrelated captured parents and 27 captive-born offspring) for the apoH protein polymorphism. The most common IEF pattern in chimpanzees was identical to a previously described APOH*3 allele in humans. In addition, an anodally shifted pattern was observed in chimpanzees with an allele frequency of 0.168, and the corresponding allele was designated as APOH*4. DNA sequencing of APOH*4 carriers revealed a missense mutation in exon 6 (A-->G) at codon 210, which replaces the amino acid lysine by glutamic acid. This mutation does not affect the binding of apoH to cardiolipin as revealed by cardiolipin/enzyme-linked immunosorbent assay (ELISA). We also evaluated the prevalence of anti-apoH antibodies in chimpanzee plasma by using human-apoH-based ELISA and the association of the Lys210Glu mutation with the occurrence of anti-apoH antibodies. The prevalence of anti-apoH antibodies in chimpanzees (64%) was found to be unusually high compared with that found in humans. However, the Lys210Glu mutation showed no association with the occurrence of anti-apoH antibodies. The prevalence of anti-apoH antibodies in chimpanzees may serve as a useful animal model for the human antiphospholipid syndrome, where these antibodies are associated with clinical manifestations.

Genetic variation in apolipoprotein H (beta2-glycoprotein I) affects the occurrence of antiphospholipid antibodies and apolipoprotein H concentrations in systemic lupus erythematosus.

Apolipoprotein H (apoH, protein; APOH, gene) is a required cofactor for the production of antiphospholipid antibodies (APA). In this study we have examined whether genetic variation in the APOH gene affects variation in risk for systemic lupus erythematosus (SLE), occurrence of antiphospholipid antibodies (APA), anti-apoH, and plasma apoH concentrations. A total of 222 white SLE women were screened for four APOH polymorphisms (codons 88, 247, 306, and 316) by polymerase chain reaction, and for plasma apoH concentrations by ELISA. Of these, 29.3% were positive for APA (APA-positive group) and 31.1% for anti-apoH. None of the four APOH polymorphisms were significantly associated with variation in risk for SLE. The codons 306 and 316 polymorphisms showed significant, gene-dosage effects on plasma apoH concentrations (P<0.0001) and explained 30% and 13%, respectively, of the residual variation in apoH concentrations. No significant association was observed between anti-apoH status and APOH polymorphisms or plasma apoH levels. However, plasma apoH concentrations were significantly higher in patients positive for APA than in patients negative for APA (18.5+/-4.0 mg/dl vs 17.1+/-3. 8 mg/dl; P=0.02). The distribution of the Trp316Ser polymorphism was significantly different between the APA-positive and APA-negative groups. The frequency of the mutant allele (Ser316) was significantly lower in the APA-positive group than the APA-negative group (3.1% vs 12.1% P<0.04), indicating that the Ser316 mutation is protective against the production of phospholipid-apoH dependent APA. Our data indicate that common genetic variation in the APOH gene is a significant determinant of plasma apoH variation in SLE patients, and the Trp316Ser polymorphism appears to provide protection against the production of APA in SLE patients.

The p22 phox polymorphism C242T is not associated with CHD risk in Asian Indians and Chinese.

BACKGROUND: Oxygen free radicals such as superoxide anion have been implicated in the pathogenesis of atherosclerosis and coronary heart disease (CHD). The nonglycosylated 22 kDa alpha-subunit of the NADH/NADPH oxidase (p22 phox) of the vasculature acts as the final electron transporter in the generation of superoxide anion. Recently, a common polymorphism (C242T) at codon 72 in the p22 phox gene has been reported to be associated with CHD risk. STUDY DESIGN: We examined the role of the C242T polymorphism with the risk of CHD in a biracial sample of Asian Indians and Chinese from Singapore. The sample comprised angiographically confirmed CHD patients (126 Asian Indians and 151 Chinese) and age- and sex-matched healthy control subjects (154 Asian Indians and 167 Chinese). RESULTS: The frequency of the T allele was significantly higher in Asian Indian control subjects than in Chinese control subjects (0.38 vs. 0.09; P < 0. 0001). However, there was no difference in the frequency of this allele between case patients and control subjects either in Chinese (0.10 vs. 0.09) or Asian Indians (0.38 vs. 0.40). This polymorphism was also not associated with plasma lipid and apolipoprotein levels in any group. CONCLUSIONS: The p22 phox codon 72 polymorphism is not associated with the risk of CHD in the present samples of Asian Indians and Chinese.

Genetic variation in the apolipoprotein H (beta2-glycoprotein I) gene affects plasma apolipoprotein H concentrations.

Apolipoprotein H (apoH, protein; APOH, gene) is a single chain glycoprotein that exists in plasma both in a free form and in combination with lipoprotein particles. ApoH has been implicated in several physiologic pathways, including lipid metabolism, coagulation, and the production of antiphospholipid antibodies. The wide range of interindividual variation in plasma apoH levels is thought to be under genetic control, but its molecular basis is unknown. APOH displays a common structural polymorphism with the occurrence of three common alleles (APOH*1, APOH*2, and APOH*3), the APOH*2 allele being the most frequent in all populations. The relationship between the APOH polymorphism and plasma apoH levels is unknown. In this study, we have determined the impact of this APOH polymorphism on apoH levels in 455 normoglycemic non-Hispanic Whites (220 men and 235 women) from the San Luis Valley, Colorado. Mean plasma apoH levels, determined by capture enzyme-linked immunosorbent assay, were 20.0 +/- 0.2 mg/dl (range: 3.4-31.2 mg/dl) with no significant difference between men and women. In women, but not in men, age had a significant effect on plasma apoH levels explaining 3.4% of its phenotypic variance. ApoH levels also correlated positively with cholesterol (P = 0.015), HDL-cholesterol (P = 0.044), and triglyceride (P = 0.037) in women, but not in men. An analysis of variance (ANOVA) of adjusted plasma apoH levels showed significant association with the APOH polymorphism in both men and women (P < 0.0001), and the APOH polymorphism accounted for 11.4% and 13.6% of the variation in apoH levels in men and women, respectively. Compared with the APOH*1 and APOH*2 alleles, the APOH*3 allele was associated with significantly lower plasma apoH levels. At the molecular level, APOH*3 can be further subdivided into two distinct forms, called APOH*3W and APOH*3B. The APOH*3W form is more common in US Whites and is the result of a missense mutation at codon 316. An ANOVA for the codon 316 polymorphism revealed that this polymorphism is a major determinant of plasma apoH variation (P < 0.0001). This study indicates that common genetic variation in the APOH gene is a significant determinant of plasma apoH levels in non-Hispanics Whites and should be useful in evaluating the role of the APOH genetic variation in various metabolic pathways in which apoH has been implicated.

Apolipoprotein J polymorphisms and serum HDL cholesterol levels in African blacks.

Apolipoprotein J (apoJ, protein; APOJ, gene) is found in serum associated with high-density lipoprotein (HDL) subfractions, which also contain apolipoprotein A-I (apoA1) and cholesteryl ester transfer protein. ApoJ has been shown to be involved in a variety of physiological functions, including lipid transport. In earlier studies we reported the existence of a common genetic polymorphism (APOJ*1 and APOJ*2 alleles) using isoelectric focusing (IEF) and immunoblotting. In this study we determined the molecular basis of this polymorphism and together with another polymorphism at codon 328 (G-->A) evaluated its relationship with serum HDL cholesterol and apoA1 levels in 767 African blacks stratified by staff level: junior (less affluent, n = 450) and senior (more affluent, n = 317). The molecular analysis of the cathodally shifted APOJ*2 allele on IEF gels revealed an amino acid substitution of asparagine by histidine resulting from a missense mutation (A-->C) at codon 317 in exon 7. The frequency of the APOJ*2 (C) allele of codon 317 in the total sample was 0.267, whereas that of the less common allele A of codon 328 was 0.04. Despite their close proximity, no linkage disequilibrium was observed between the 2 polymorphisms. The impact of the codon 317 polymorphic variation was significant on serum HDL cholesterol (p = 0.003) and HDL3 cholesterol (p = 0.001) in junior staff. The adjusted mean values of these traits were higher in the codon 317 APOJ*2/*2 genotype than in the *1/*1 and *1/*2 genotypes. Overall, the APOJ codon 317 polymorphism explained 10.2% and 8.3% of the phenotypic variation in HDL cholesterol and HDL3 cholesterol, respectively, in junior staff. The codon 328 polymorphism showed a significant effect on HDL2 cholesterol (p = 0.039) and apoA1 (p = 0.007) only in junior women and accounted for 2.5% and 4.2% of the phenotypic variation in HDL2 cholesterol and apoA1, respectively. We also analyzed the combined effects of these genotypes at the 2 polymorphic sites. Significant effects on HDL cholesterol (p = 0.004) and HDL3 cholesterol (p = 0.008) in junior men and on HDL2 cholesterol (p = 0.003) in junior women were observed in the combined genotype data. The 2-locus genotypes explained 6.0% and 5.3% of the residual phenotypic variation of HDL cholesterol and HDL3 cholesterol in junior men and 10.4% of HDL2 cholesterol in junior women. These data indicate that the effect of the APOJ polymorphism on HDL cholesterol levels is modulated by socioeconomic status, as measured by staff level. Given the association of HDL and its subfractions with cardiovascular disease, these polymorphisms may lead to a better understanding of interracial differences in the risk of cardiovascular disease.

Structure of the human beta2-glycoprotein I (apolipoprotein H) gene.

The gene encoding the human plasma protein beta2-glycoprotein I or apolipoprotein H was cloned and its structure determined. The gene which consists of eight exons was shown to span 18 kb and was localized to chromosome 17q23-24. The transcriptional initiation site was assigned to a position 31 bp upstream of the start codon. Several consensus sequence elements relevant for regulation of transcription in liver were seen in the 5'-upstream region of the gene. Exon 1 contains the 5'-UTR together with the signal peptide coding sequences. Short consensus repeats (SCRs) 1, 3, 4, and 5 are encoded by single exons each while SCR2 is encoded by two exons. Exon 8 comprises the region encoding the C-terminal end of beta2-glycoprotein I (from His-310), the stop codon and the 3'-UTR.

The codon 55 polymorphism in the paraoxonase 1 gene is not associated with the risk of coronary heart disease in Asian Indians and Chinese.

Recently several but not all studies have implicated the codon 192 polymorphism in the paraoxonase 1 (PON1) gene with the risk of coronary heart disease (CHD). These findings suggest that this polymorphism is not functional but rather may be in linkage disequilibrium with a functional mutation in the PON1 or a nearby gene. In this investigation, we have evaluated the role of another common polymorphism in the PON1 gene at codon 55 with the risk of CHD in a biracial sample of Asian Indians and Chinese. We observed a significant inter-racial variability in the allelic distribution as the frequency of the less common allele, codon 55/L, was significantly higher in Indians than Chinese (0.202 versus 0.036; P < 0.0001). However, despite this inter-racial difference the codon 55 polymorphism was neither associated with CHD risk nor with plasma lipoprotein-lipids variation in both racial groups. We also used two site haplotype data (codons 55 and 192) to assess the combined contribution of the two polymorphisms to the risk of CHD. There was a strong linkage disequilibrium between the two polymorphic sites in both racial groups (P < 0.0001). While the haplotype data revealed no association with CHD in Chinese, the frequency of the BL haplotype was significantly higher (0.430 versus 0.311; P = 0.004) and the frequency of the AL haplotype was significantly lower (0.368 versus 0.483; P = 0.006) in Indian patients than controls. Since the B allele of the codon 192 polymorphism was shown to be an independent risk factor for CHD in Indians in our previous study, the positive association of the BL haplotype with CHD appears to be mediated by the B allele with no independent contribution from the codon 55 polymorphism.

Racial differences in the distribution of a low density lipoprotein receptor-related protein (LRP) polymorphism and its association with serum lipoprotein, lipid and apolipoprotein levels.

The low density lipoprotein (LDL) receptor-related protein (LRP) is a cell receptor that has close structural homology to the LDL and very low density lipoprotein receptors and thus is believed to play an important role in lipid metabolism. This study was carried out to evaluate the distribution of a known tetranucleotide repeat polymorphism in the LRP gene and its association with serum lipoprotein-lipid and apolipoprotein levels in four large samples comprising Hispanics (n=373) and non-Hispanic Whites (n=522) from the U.S. and Nigerian Blacks from Sokoto (n=390) and Benin (n=800). A total of four alleles, designated 83, 87, 91 and 95 bp, were observed. The 83 bp allele was observed at 0.4-1.1% in the two U.S. populations but was completely absent in African Blacks. Sokoto Blacks had significantly different frequencies of the 87 and 91 bp alleles compared to Hispanics (P=0.008) and non-Hispanic Whites (P=0.024). The frequency of the 91 bp allele was also significantly higher in Benin Blacks compared to Hispanics (P=0.026) and non-Hispanic Whites (P=0.054). The analysis of the relationship between the LRP polymorphism and serum lipid traits yielded some significant race and gender specific significant association for lipoprotein(a) in non-Hispanic White males (P=0.02); HDL2-cholesterol in Hispanic females (P=0.03) and apolipoprotein B in Benin males (P=0.04). We also observed an interaction between the LRP polymorphism and menopausal status for Lp(a) in Hispanic females (P=0.014). However, considering multiple comparisons were performed, these associations could be due to chance. Our data indicate that although the LRP tetranucleotide polymorphism exhibits inter-racial differences in its distribution, it does not appear to have a significant role in affecting serum lipid traits.

DNA polymorphisms in two paraoxonase genes (PON1 and PON2) are associated with the risk of coronary heart disease.

A common polymorphism at codon 192 in the human paraoxonase (PON) 1 gene has been shown to be associated with increased risk for coronary heart disease (CHD) in Caucasian populations. However, these findings have not been reported consistently in all Caucasian and non-Caucasian populations, suggesting that this is not a functional mutation but may mark a functional mutation present in either PON1 or a nearby gene. Recently, two other PON-like genes, designated "PON2" and "PON3," have been identified, and they are linked with the known PON1 gene on chromosome 7. Identification of additional polymorphisms in the PON-gene cluster may help to locate the functional polymorphism. In this report, we describe the existence of a common polymorphism at codon 311 (Cys-->Ser; PON2*S) in the PON2 gene, as well as its association with CHD alone and in combination with the PON1 codon 192 polymorphism in Asian Indians. The frequency of the PON2*S allele was significantly higher in cases than in controls (.71 vs. .61; P=.016). The age- and sex-adjusted odds ratio (OR) was 2.5 (95% confidence interval &sqbl0;95% CI&sqbr0;=1.8-3.1; P=.0090) for the PON2*S allele carriers. Further stratification of the PON2*S association, on the basis of the presence or absence of the PON1*B allele, showed that the CHD risk associated with the PON2*S allele was confined to PON1*B-allele carriers. Likewise, the PON1*B-allele risk was present only among PON2*S carriers. Age- and sex-adjusted ORs for the PON2*S and PON1*B were 3.6 (95% CI=2.6-4.6; P=.011) and 2.9 (95% CI=2.4-3.5; P=.0002) among the PON1*B and PON2*S carriers, respectively. Our data indicate that both polymorphisms synergistically contribute to the CHD risk in this sample and that this genetic risk is independent of the conventional plasma lipid profile.

Molecular basis of the apolipoprotein H (beta 2-glycoprotein I) protein polymorphism.

Apolipoprotein H (apoH, protein; APOH, gene) is considered to be an essential cofactor for the binding of certain antiphospholipid autoantibodies to anionic phospholipids. APOH exhibits a genetically determined structural polymorphism due to the presence of three common alleles (APOH*1, APOH*2 and APOH*3) detectable by isoelectric focusing (IEF) and immunoblotting. The APOH*3 allele can be further characterized into two subtypes, APOH*3w and APOH*3B, based upon its reactivity with monoclonal antibody 3D11. In this study we have determined the molecular basis of the APOH protein polymorphism and its distribution in three large U.S. population samples comprising 661 non-Hispanic whites, 444 Hispanics and 422 blacks. By direct DNA sequencing of PCR amplified fragments corresponding to the eight APOH exons, we identified two missense mutations that correspond to the APOH*1 and APOH*3w alleles. A missense mutation (G-->A) in exon 3, which alters amino acid Ser to Asn at codon 88 and creates a restriction site for TSP509 I, was present in all APOH*1 allele carriers. A second missense mutation (G-->C) at codon 316 in exon 8, which replaces amino acid Trp with Ser and creates a restriction site for BSTBI, was present in all APOH*3w carriers. The distribution of the Ser 88 Asn and Trp 316 Ser mutations was significantly different between the three racial groups. The frequency of the Asn-88 allele was 0.011, 0.043, and 0.056 in blacks. Hispanics and non-Hispanic whites, respectively. While the Ser-316 allele was observed sporadically in blacks (0.008), it was present at a polymorphic frequency in Hispanics (0.027) and non-Hispanic whites (0.059). The identification of the molecular basis of the APOH protein polymorphism will help to elucidate the structural-functional relationship of apoH in the production of antiphospholipid autoantibodies.

Genetic polymorphism of paraoxonase and the risk of coronary heart disease.

Recent studies have implicated paraoxonase, an HDL-associated enzyme, in providing protection against LDL oxidation, thus affecting the risk of coronary heart disease (CHD) in the general population. In this study, we evaluated the distribution of a biallelic PON polymorphism at codon 192 (A and B alleles) and its relationship with plasma lipids and CHD in two racial groups comprising Asian Indians and Chinese from Singapore. The frequency of the B allele was significantly higher in Chinese control subjects than in Indian control subjects (0.58 versus 0.33; P < .0001). With the exception of a marginal effect on apolipoprotein A-I levels in Indians, no other significant association was observed between the PON polymorphism and quantitative lipid traits in either racial group. However, there was a race-specific association of the B allele with CHD in Indians but not in Chinese. The Indian CHD patients had a significantly higher frequency of the B allele than control subjects (.43 versus .33; P = .014). The age- and sex-adjusted odds ratio for developing CHD with the B allele (BB+AB genotypes) was 2.01 (95% CI, 1.17 to 3.45; P = .011) compared with the A allele (AA genotype). When the Indian patients were stratified into subgroups, the association remained significant in nondiabetic patients (odds ratio, 2.29; P = .008), and it became stronger in patients with myocardial infarction (odds ratio, 2.94; P = .004) than in patients without myocardial infarction (odds ratio, 1.11; P = .76). These data indicate that a common polymorphism in the PON gene is an independent risk factor for CHD in populations with white ancestry.

Identification of structural mutations in the fifth domain of apolipoprotein H (beta 2-glycoprotein I) which affect phospholipid binding.

Apolipoprotein H (apoH), also known as beta 2-glycoprotein-I, is considered to be a cofactor for the binding of certain antiphospholipid autoantibodies to negatively charged phospholipids. Genetically determined structural abnormalities in the lipid binding domain(s) of apoH can affect its ability to bind lipid and consequently the production of the autoantibodies. In this study we have identified two common structural mutations at codons 316 and 306 in the fifth domain of apoH which rendered apoH unable to bind to negatively charged phosphatidylserine (PS). The missense mutation at codon 316 (TGG --> TCG) replaces Trp316 with Ser316 and disrupts the integrity of four highly conserved hydrophobic amino acids sequence at positions 313-316, which is a potential protein-lipid hydrophobic interaction site. The missense mutation at codon 306 (TGC --> GGC) involves the substitution of Cys306 by Gly306 which causes the disruption of a disulfide bond between Cys281 and Cys306 and affects the normal configuration of the fifth domain of apoH that appears to be critical for clustering positively charged amino acids along with four hydrophobic amino acids sequence. ApoH from the two homozygotes (Ser316/Ser316) and all seven compound heterozygotes (Ser316/Gly306) failed to bind to PS; all heterozygotes at one or the other sites and wild type showed normal PS binding. These data indicate that the fifth domain of apoH harbors the lipid binding region. An estimated 2 million Caucasians in the United States, who are compound heterozygotes for the two mutations, may be precluded from producing apoH-dependent antiphospholipid autoantibodies.

Gender-specific nonrandom association between the alpha 1-antichymotrypsin and apolipoprotein E polymorphisms in the general population and its implication for the risk of Alzheimer's disease.

A common polymorphism in the alpha 1-antichymotrypsin (ACT) gene has been found co modify the APOE*4-associated risk of Alzheimer's disease due to an apparent interaction between the two loci. This study was undertaken to determine the gender- and age-related distributions of these two polymorphisms in two large population-based samples of Caucasians (n = 803) and Nigerian Blacks (n = 730). Significantly higher frequencies of the ACT*A (78.6% vs. 48.4%; P < 0.001) and APOE*4 (25.6% vs. 15.6%; P < 0.001) alleles were observed in Nigerian Blacks than in Caucasians. In Caucasian women but not in men, the frequency of the APOE*4 allele was significantly lower in the ACT/AA genotype as compared to the ACT/AT and ACT/TT genotypes, while a reverse trend was seen for the APOE*3 allele frequency among the ACT genotypes. The distribution of the ACT*A allele between the APOE*4 carriers and non-APOE*4 carriers was also different in Caucasian women but not in men. A similar gender-specific nonrandom association between the two polymorphisms was observed in Black women but this was not as strong as observed in Caucasian women. When the two samples were stratified by age group, an association or trend of association was observed in all age groups in women only. These data indicate the existence of a nonrandom association between the APOE and ACT loci in women which may have an important implication for the higher prevalence of Alzheimer's disease in women.

Quantitative effects of the apolipoprotein E polymorphism in a biracial sample of 9-10-year-old girls.

Genetic polymorphism at the apolipoprotein E locus (APOE) has been shown to have a significant impact on quantitative risk factors for coronary artery disease (CAD) in diverse populations. However, despite the recognition that atherosclerosis begins in childhood and that genetic factors are related to the initial stages of atherosclerosis, prior studies were carried out mostly on adults and little attention has been paid to genetic risk factors for CAD in children. We have examined the impact of APOE polymorphism on quantitative risk factors for CAD (apoAI, apoB, TC, LDL-C, HDL-C and TG) in a sample of 647 African American and 573 White 9-10-year-old girls who were enrolled in the National Heart, Lung and Blood Institute Growth and Healthy Study. The frequencies of the APOE*2, APOE*3 and APOE*4 alleles were 0.09, 0.76 and 0.15 in Whites and 0.11, 0.70 and 0.19 in African Americans, respectively. The APOE*2 allele was significantly associated with lower mean levels of LDL-C and apoB and the APOE*4 allele with higher levels of LDL-C and apoB in both racial groups. Variation in maturation stage, body fat and fat patterning, as assessed by skin fold measures and waist/hip ratio, accounted for a significant proportion of the variation in quantitative CAD risk factors.

APOE*4-associated Alzheimer's disease risk is modified by alpha 1-antichymotrypsin polymorphism.

Genetic studies on Alzheimer's disease (AD), a devastating neurodegenerative disorder, have identified the apolipoprotein E (APOE) gene as a strong susceptibility marker for AD. The E*4 allele of APOE is a major risk factor for AD regardless of age of onset or family history. However, the observation that the APOE*4 allele is neither necessary nor sufficient for the expression of AD emphasizes the involvement of other environmental or genetic elements that, either in conjunction with APOE*4 or alone, increase an individual's risk of developing AD. Among the candidate genes that may affect the risk of this multifactorial disease is the gene coding for alpha 1-antichymotrypsin (ACT). Like APOE protein, ACT binds to beta-amyloid peptide (A beta P) with high affinity in the filamentous deposits found in the AD brain and serves as a strong stimulatory factor in the polymerization of A beta P into amyloid filaments. In AD brains, ACT expression is enhanced, particularly in areas that develop amyloid plaques, suggesting that ACT may play an important role in the pathogenesis of AD. Here we show that a common polymorphism in the signal peptide of ACT confers a significant risk for AD. Furthermore, the APOE*4 gene dosage effect associated with AD risk is significantly modified by the ACT polymorphism. We have also identified a unique combination of the ACT/AA and APOE 4/4 genotypes as a potential susceptibility marker for AD, as its frequency was 1/17 in the AD group compared to 1/313 in the general population control. Our data show that ACT behaves as a modifier gene that alters the AD risk conventionally associated with the APOE*4 allele.