QTL-based association analyses reveal novel genes influencing pleiotropy of metabolic syndrome (MetS).

OBJECTIVE: Metabolic Syndrome (MetS) is a phenotype cluster predisposing to type 2 diabetes and cardiovascular disease. We conducted a study to elucidate the genetic basis underlying linkage signals for multiple representative traits of MetS that we had previously identified at two significant QTLs on chromosomes 3q27 and 17p12. DESIGN AND METHODS: We performed QTL-specific genomic and transcriptomic analyses in 1,137 individuals from 85 extended families that contributed to the original linkage. We tested in SOLAR association of MetS phenotypes with QTL-specific haplotype-tagging SNPs as well as transcriptional profiles of peripheral blood mononuclear cells (PBMCs). RESULTS: SNPs significantly associated with MetS phenotypes under the prior hypothesis of linkage mapped to seven genes at 3q27 and seven at 17p12. Prioritization based on biologic relevance, SNP association, and expression analyses identified two genes: insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) at 3q27 and tumor necrosis factor receptor 13B (TNFRSF13B) at 17p12. Prioritized genes could influence cell-cell adhesion and adipocyte differentiation, insulin/glucose responsiveness, cytokine effectiveness, plasma lipid levels, and lipoprotein densities. CONCLUSIONS: Using an approach combining genomic, transcriptomic, and bioinformatic data we identified novel candidate genes for MetS.

A quantitative trait locus on chromosome 5p influences d-dimer levels in the san antonio family heart study.

Background. D-dimer is associated with increasing severity of atherosclerosis and with increased risk of a cardiovascular disease (CVD). Methods and Results. To better understand this risk factor, we performed a genome scan on 803 (301 males and 502 females) Mexican Americans in the San Antonio Family Heart Study (SAFHS). The SAFHS is ideal for the discovery of quantitative trait loci (QTLs) influencing CVD because CVD risk factors are prevalent in Mexican Americans of San Antonio and because the study design involves large families, which is optimal for QTL discovery. D-dimer levels were normalized in our study. We found that D-dimer levels were heritable, at about 23% heritability (P ≈ .00001). In a linkage analysis employing 432 microsatellite markers, we found strong evidence of a QTL on chromosome 5p with a lod score of 3.32 at 21 centiMorgans (cM). We also found suggestive evidence of a QTL on chromosome 2q with a lod score of 2.33 at 207 cM. Conclusions. To our knowledge, the putative QTL on chromosome 5p is novel. The possible QTL on chromosome 2q is discussed in relation to a recent report of linkage of a related hemostatic factor to the same location. These results warrant further investigation.

Determinants of variation in human serum paraoxonase activity.

Paraoxonase-1 (PON1) is associated with high-density lipoprotein (HDL) particles and is believed to contribute to antiatherogenic properties of HDLs. We assessed the determinants of PON1 activity variation using different substrates of the enzyme. PON1 activity in serum samples from 922 participants in the San Antonio Family Heart Study was assayed using a reliable microplate format with three substrates: paraoxon, phenyl acetate and the lactone dihydrocoumarin. There were major differences among results from the three substrates in degree of effect by various environmental and genetic factors, suggesting that knowledge of one substrate activity alone may not provide a complete sense of PON1 metabolism. Three significant demographic covariates (age, smoking status and contraceptive usage) together explained 1-6% of phenotypic variance, whereas four metabolic covariates representing lipoprotein metabolism (apoAII, apoAI, triglycerides and non-HDL cholesterol) explained 4-19%. Genes explained 65-92% of phenotypic variance and the dominant genetic effect was exerted by a locus mapping at or near the protein structural locus (PON1) on chromosome 7. Additional genes influencing PON1 activity were localized to chromosomes 3 and 14. Our study identified environmental and genetic determinants of PON1 activity that accounted for 88-97% of total phenotypic variance, suggesting that few, if any, major biological determinants are unrepresented in the models.

A pleiotropic QTL on 2p influences serum Lp-PLA2 activity and LDL cholesterol concentration in a baboon model for the genetics of atherosclerosis risk factors.

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), the major portion of which is bound to low-density lipoprotein, is an independent biomarker of cardiovascular disease risk. To search for common genetic determinants of variation in both Lp-PLA(2) activity and LDL cholesterol (LDL-C) concentration, we assayed these substances in serum from 679 pedigreed baboons. Using a maximum likelihood-based variance components approach, we detected significant evidence for a QTL affecting Lp-PLA(2) activity (LOD=2.79, genome-wide P=0.039) and suggestive evidence for a QTL affecting LDL-C levels (LOD=2.16) at the same location on the baboon ortholog of human chromosome 2p. Because we also found a significant genetic correlation between the two traits (rho(G)=0.50, P<0.00001), we conducted bivariate linkage analyses of Lp-PLA(2) activity and LDL-C concentration. These bivariate analyses improved the evidence (LOD=3.19, genome-wide P=0.015) for a QTL at the same location on 2p, corresponding to the human cytogenetic region 2p24.3-p23.2. The QTL-specific correlation between the traits (rho(Q)=0.62) was significantly different from both zero and 1 (P[rho(Q)=0]=0.047; P[rho(Q)=1]=0.022), rejecting the hypothesis of co-incident linkage and consistent with incomplete pleiotropy at this locus. We conclude that polymorphisms at the QTL described in this study exert some genetic effects that are shared between Lp-PLA(2) activity and LDL-C concentration.

Collaborative meta-analysis of individual participant data from observational studies of Lp-PLA2 and cardiovascular diseases.

BACKGROUND: A large number of observational epidemiological studies have reported generally positive associations between circulating mass and activity levels of lipoprotein-associated phospholipase A2 (Lp-PLA2) and the risk of cardiovascular diseases. Few studies have been large enough to provide reliable estimates in different circumstances, such as in different subgroups (e.g., by age group, sex, or smoking status) or at different Lp-PLA2 levels. Moreover, most published studies have related disease risk only to baseline values of Lp-PLA2 markers (which can lead to substantial underestimation of any risk relationships because of within-person variability over time) and have used different approaches to adjustment for possible confounding factors. OBJECTIVES: By combination of data from individual participants from all relevant observational studies in a systematic 'meta-analysis', with correction for regression dilution (using available data on serial measurements of Lp-PLA2), the Lp-PLA2 Studies Collaboration will aim to characterize more precisely than has previously been possible the strength and shape of the age and sex-specific associations of plasma Lp-PLA2 with coronary heart disease (and, where data are sufficient, with other vascular diseases, such as ischaemic stroke). It will also help to determine to what extent such associations are independent of possible confounding factors and to explore potential sources of heterogeneity among studies, such as those related to assay methods and study design. It is anticipated that the present collaboration will serve as a framework to investigate related questions on Lp-PLA2 and cardiovascular outcomes. METHODS: A central database is being established containing data on circulating Lp-PLA2 values, sex and other potential confounding factors, age at baseline Lp-PLA2 measurement, age at event or at last follow-up, major vascular morbidity and cause-specific mortality. Information about any repeat measurements of Lp-PLA2 and potential confounding factors has been sought to allow adjustment for possible confounding and correction for regression dilution. The analyses will involve age-specific regression models. Synthesis of the available observational studies of Lp-PLA2 will yield information on a total of about 15 000 cardiovascular disease endpoints.

Quantitative trait locus on chromosome 12q14.1 influences variation in plasma plasminogen levels in the San Antonio Family Heart Study.

Plasminogen is a hemostasis-related phenotype and is commonly implicated in thrombotic and bleeding disorders. In the San Antonio Family Heart Study (SAFHS), we performed to our knowledge the first genomewide linkage scan for quantitative trait loci (QTLs) that influence the level of plasminogen. The subset of the SAFHS population used for this study consists of 629 individuals distributed across 26 extended Mexican American families. Pedigree-based variance component linkage analyses were performed using SOLAR. The mean plasminogen level was 114.94% +/- 17.8 (range, 42-195). The heritability (h2) of plasminogen was 0.43 +/- 0.08 (p < 6.3 x 10(-13)). One region on chromosome 12 (12q14.1) showed suggestive evidence of linkage (LOD = 2.73, nominal p < 0.0002, genomewide p = 0.0786) near marker D12S1609. Because plasminogen has important effects in many human health problems, such as cancer and atherosclerosis, the role of this putative QTL in the regulation of plasminogen variability needs to be studied further.

Effects of diabetes on plasma nitrotyrosine levels.

BACKGROUND: Oxidative stress plays a major role in disease processes such as atherosclerosis and diabetes. Peroxynitrite is a reaction product of nitric oxide (NO) and superoxide and a potent oxidant. The peroxynitrite-mediated tyrosine nitration, which forms nitrotyrosine (NT), is associated with several pathological conditions. METHODS: We measured plasma NT levels using the HPLC method in 40 Mexican Americans with diabetes, but not taking medications, and 40 age- and sex-matched euglycaemic controls. RESULTS: Plasma-free NT levels were not different between subjects with diabetes (11.0 +/- 1.7 nmol/l, n = 40) and with non-diabetes (10.4 +/- 1.5 nmol/l, n = 40). There was also no association with levels of fasting glucose (r = -0.049, P = 0.663) or 2-h glucose (r = -0.099, P = 0.390). However, females had significantly lower free NT level (7.6 +/- 1.4 nmol/l, n = 40) than males (13.8 +/- 1.7 nmol/l, n = 40, P = 0.005), which were not affected by age, smoking status, BMI and glucose levels. CONCLUSIONS: In contrast to some earlier reports, our study shows that diabetes has no effect on plasma NT levels in Mexican Americans. We have also demonstrated lower free NT levels in females than males, which may partly explain the lower risk profile to vascular disease in women.

Effects of lipids and lipid-lowering therapy on hemostatic factors in patients with myocardial infarction.

BACKGROUND: The risk of cardiovascular disease (CVD) is associated with specific hemostatic markers and lipid profiles, and evidence indicates that there are associations between lipid profiles and the levels of certain hemostatic factors. The disturbances in hemostasis and the risk of CVD can be ameliorated by lipid-lowering therapy. OBJECTIVE: We investigated the associations of lipid profiles with factor (F)VIIa, von Willebrand factor (VWF), D-dimer and plasminogen activator inhibitor-1 (PAI-1), and examined whether lipid-lowering statin therapy would affect the levels of these hemostatic markers. PATIENTS AND METHODS: This cross-sectional study analyzed 1045 postmyocardial infarction patients. RESULTS: In multivariate regression analyses (without adjusting for clinical covariates) HDL-cholesterol (HDL-C) and HDL size were independent and significant predictors of FVIIa; HDL size was a predictor of VWF; HDL size, HDL-C and LDL size were predictors of D-dimer; and triglyceride and HDL size were predictors of PAI-1. After adjusting for clinical covariates, HDL-C, lipoprotein (Lp)(a), apolipoprotein B (apoB) and warfarin were independent and significant predictors of FVIIa; HDL size, age, diabetes mellitus, insulin, race and warfarin were predictors of VWF; HDL-C, HDL size, LDL size, age, warfarin, hypertension and gender were predictors of D-dimer; and triglyceride, HDL size, body mass index, insulin and hypertension were predictors of PAI-1. Patients on statin therapy had significantly lower levels of D-dimer than those who were not on this therapy. CONCLUSION: There are significant associations of lipid profiles with hemostatic factors, the directions of which suggest novel pathways by which dyslipidemia may contribute to coronary heart disease.

A quantitative trait locus on chromosome 16q influences variation in plasma HDL-C levels in Mexican Americans.

OBJECTIVE: We conducted a whole-genome, multipoint linkage screen to localize a previously reported major locus accounting for 56% to 67% of the additive genetic effects on covariate-adjusted plasma HDL cholesterol (HDL-C) levels in Mexican Americans from the San Antonio Family Heart Study (SAFHS). METHODS AND RESULTS: After using complex segregation analysis to recover the major locus in 472 SAFHS participants from 10 genotyped families, we incorporated covariates required to detect that major locus, including plasma levels of triglycerides and apolipoprotein A-I, in a maximum-likelihood-based variance-components linkage screen. Only chromosome 16 exhibited convincing evidence for a quantitative trait locus (QTL), with a peak multipoint log of the odds (LOD)=3.73 (P=0.000034). Subsequent penetrance model-based linkage analysis, incorporating genotypes at the marker locus nearest the multipoint peak (D16S518) into the segregation model, detected linkage with the previously detected major locus (LOD=2.73, P=0.000642). Initial estimates place this QTL within a 15-cM region of chromosome 16q near the structural loci for lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP). CONCLUSIONS: A QTL influencing plasma levels of HDL-C in Mexican Americans from San Antonio maps to a region of human chromosome 16q near LCAT and CETP.

Genetic control of coordinated changes in HDL and LDL size phenotypes.

We investigated the correlation of high density lipoprotein (HDL) and low density lipoprotein (LDL) particle size distributions in samples from >1100 participants in the San Antonio Family Heart Study. By use of analyses of individual correlations of each HDL fraction with each LDL fraction, we devised new metrics for particle size phenotype, termed DeltaHDL and DeltaLDL, to optimally reflect the size correlations. Confirming previous studies, we found that the 2 size phenotype variables were positively correlated (r=0.51). Quantitative genetic analysis indicated that nearly half (44%) of the variance in DeltaHDL and in DeltaLDL was explained by the additive effects of genes. Bivariate genetic analyses indicated that a positive genetic correlation (rho(G)=0.56) exists between them and suggested that the pleiotropic effects of a gene or group of genes account for approximately 31% [ie, rho(G)(2) =(0.56)(2)=0.31] of the genetic variance in the 2 traits. Triglyceride (TG) levels were negatively related to DeltaHDL and DeltaLDL, with phenotypic correlations of -0.48 and -0.58, respectively, and genetic correlations of -0.45 and -0.76, respectively, suggesting that genes exert significant pleiotropic effects on the covariation of TGs with each of the size variables. Finally, we evaluated a bivariate model for DeltaHDL and DeltaLDL in which TG level was included as a covariate. This analysis indicated that a small but significant genetic correlation remains for DeltaHDL and DeltaLDL, even after accounting for the effects of TGs. Thus, our study demonstrates that the phenotypic correlation of HDL and LDL sizes results in part from the pleiotropic actions of a set of genes, some of which also influence TG levels and some of which do not.

Genetic contributions to plasma total antioxidant activity.

Oxidative stress plays important roles in a wide spectrum of pathological processes, such as atherosclerosis. Although several environmental factors are documented to influence redox metabolism, relatively little is known about genetic effects. In the present study, we evaluated genetic contributions to variation in plasma total antioxidant status (TAS), a measure of peroxyl-scavenging capacity, in 1337 members of 40 Mexican American families. TAS levels were significantly lower in women than in men (1.675+/-0.004 versus 1.805+/-0.005 mmol/L, respectively; P<0.001), and there was a significant decline of TAS levels with age in men but not in women (P<0.01 for the interaction). Quantitative genetic analysis indicated the heritability of TAS levels to be 0.509+/-0.052; ie, approximately 51% of the residual variance (after covariate adjustment) in TAS levels was due to the additive effects of genes (P<0.001). We have further observed a significant gene-by-smoking interaction (P<0.05). Additive genetic effects account for 83% of the residual phenotypic variance in TAS levels among smokers, but they account for only 49% in nonsmokers. However, genes contributing to TAS variation are the same in smokers and nonsmokers. Our study for the first time demonstrates that TAS, an indicator of redox homeostasis, is under strong genetic control, especially among smokers. With appropriate tools, such as genome screening, it should be possible to localize genes that regulate redox homeostasis and, ultimately, identify the DNA sequence variants predisposing subjects to oxidative damage.

Association among 5-year changes in weight, physical activity, and cardiovascular disease risk factors in Mexican Americans.

Recent changes in lifestyle have led to a global epidemic of obesity. To determine the associations of these changes with cardiovascular disease (CVD) risk, the authors correlated changes in CVD risk factors with changes in weight and physical activity in a population-based sample of 539 Mexican Americans in the San Antonio Heart Study in 1992-1999 who were examined twice approximately 5 years apart. Average weight change during that interval was 2.7 kg. While change in physical activity (expressed as percent change) was associated modestly only with change in low density lipoprotein cholesterol median diameter (p = 0.017), weight change was strongly and positively associated with unfavorable changes in lipid and lipoprotein traits, insulin levels, and blood pressure, explaining 2-10% of the variation in the risk factor changes during the interval. The unfavorable associations with weight gain tended to be more pronounced in lean compared with obese individuals and in men compared with women. However, the associations were significant for most CVD risk factors in all groups. In Mexican Americans, a population at high risk for obesity, weight change was positively correlated with metabolic variables associated with risk of CVD. Therefore, increasing adiposity in this population may tend to slow, or even reverse, the decline in CVD morbidity and mortality.

Effects of the ApoE polymorphism on plasma lipoproteins in Mexican Americans.

PURPOSE: To evaluate the impact of apolipoprotein E (apoE) genotypes on lipoprotein measurements relative to that of other known cardiovascular risk factors in participants of a large population-based family study. METHODS: We measured concentrations of apoE, the major constituents of HDL (cholesterol, apoAI), LDL-C (cholesterol and apoB), and fraction of apoE in lipoprotein size classes in 859 participants of the San Antonio Family Heart Study, and then tested the association between the three common apoE genotypes (epsilon2epsilon3, epsilon3epsilon3, and epsilon3epsilon4) and lipoprotein traits using the measured genotype approach to account for residual familial correlations. RESULTS: Allele frequencies in this population for epsilon2, epsilon3, and epsilon4 were 3.5%, 89.6%, and 6.9%, respectively. As expected, adjusted apoE concentrations were highest in those with epsilon2epsilon3, intermediate in those with epsilon3epsilon3, and lowest in those with epsilon3epsilon4. The concentrations of total cholesterol, LDL-C and apoB were lowest in those with epsilon2epsilon3, intermediate in those with epsilon3epsilon3, and highest in those with epsilon3epsilon4. There was no significant effect of apoE genotypes on triglycerides, HDL-C, or apoAI levels. Compared to subjects with epsilon3epsilon4, subjects with epsilon2epsilon3 had relatively less apoE in LDL and HDL(1), and relatively more in HDL(2) and HDL(3) size fractions. The effect of apoE genotypes was significantly greater on apoB in women than in men. ApoE genotypes accounted for 4.5%, 12.3%, and 4.7% of the total genetic variation in apoB, apoE, and LDL-C, respectively. CONCLUSION: ApoE genotypes account for a modest, albeit significant, proportion of phenotypic variation in concentrations of LDL-C, apoB, and apoE, and distributions of apoE among lipoproteins in this population; these genotypes have a greater effect on apoB levels in women than in men.

Lipoprotein correlates of LDL particle size.

Correlations of low-density lipoprotein (LDL) predominant particle diameters (PPD) were investigated in samples taken from the San Antonio Family Heart Study. A frequency histogram showed LDL PPD occurs in at least two distinct modes, at about 25.5 and 26.9 nm, with the nadir at about 26.2 nm. Triglyceride (TG) concentrations were strongly correlated with LDL PPD, accounting for nearly 50% of the variation. However, examination of the relationship between TG concentrations and LDL PPD showed considerable overlap of the two LDL size categories for samples having intermediate levels of TG (1-3 mmol/l). In order to examine the factors associated with particle size variation within this region of overlap, 163 pairs of samples, which contrasted peak particle diameters, were matched for TG concentrations and for sex and age. In this matched set, LDL-related measures (i.e. LDL-C, apoB, apoE, and TG concentrations) did not differ. However, several high-density lipoprotein (HDL) measures were significantly related to the LDL particle size category. This category predicted a substantial proportion of variation in HDL-C (9.7%) and apoAI (7.5%) concentrations, and in HDL size distributions of cholesterol (13.6%) and apoAI (10.3%). Other traits related to insulin resistance syndrome (IRS) (glucose and insulin concentrations, blood pressure, and adiposity measures) were tested for association with the LDL size category. None of these traits were related to LDL size after adjusting for TG, except fasting and postchallenge glucose concentrations which showed modest correlations (P-values were 0.02 and 0.05, respectively). The data suggest that in addition to the strong effects of TG, there is also an aspect of LDL particle size variation that is strongly associated with variation in HDL concentration and particle size distribution, perhaps reflecting common metabolic determinants of lipoprotein size.

Evidence that multiple genes influence baseline concentrations and diet response of Lp(a) in baboons.

We investigated the response of lipoprotein(a) [Lp(a)] levels to dietary fat and cholesterol in 633 baboons fed a series of 3 diets: a basal diet low in cholesterol and fat, a high-fat diet, and a diet high in fat and cholesterol. Measurement of serum concentrations in samples taken while the baboons were sequentially fed the 3 diets allowed us to analyze 3 Lp(a) variables: Lp(a)(Basal), Lp(a)(RF) (response to increased dietary fat), and Lp(a)(RC) (response to increased dietary cholesterol in the high-fat environment). On average, Lp(a) concentrations significantly increased 6% and 28%, respectively, when dietary fat and cholesterol were increased (P<0.001). As expected, most of the variation in Lp(a)(Basal) was influenced by genes (h(2)=0.881). However, less than half of the variation in Lp(a)(RC) was influenced by genes (h(2)=0.347, P<0. 0001), whereas the increase due to dietary fat alone was not significantly heritable (h(2)=0.043, P=0.28). To determine whether Lp(a) phenotypic variation was due to variation in LPA, the locus encoding the apolipoprotein(a) [apo(a)] protein, we conducted linkage analyses by using LPA genotypes inferred from the apo(a) isoform phenotypes. All of the genetic variance in Lp(a)(Basal) concentration was linked to the LPA locus (log of the odds [LOD] score was 30.5). In contrast, linkage analyses revealed that genetic variance in Lp(a)(RC) was not linked to the LPA locus (LOD score was 0.036, P>0.5). To begin identifying the non-LPA genes that influence the Lp(a) response to dietary cholesterol, we tested, in bivariate quantitative genetic analyses, for correlation with low density lipoprotein cholesterol [LDLC; ie, non-high density lipoprotein cholesterol less the cholesterol contribution from Lp(a)]. LDLC(Basal) was weakly correlated with Lp(a)(Basal) (rho(P)=0.018). However, LDLC(RC) and Lp(a)(RC) were strongly correlated (rho(P)=0. 382), and partitioning the correlations revealed significant genetic and environmental correlations (rho(G)=0.587 and rho(E)=0.251, respectively). The results suggest that increasing both dietary fat and dietary cholesterol caused significant increases in Lp(a) concentrations and that the response to dietary cholesterol was mediated by a gene or suite of genes that appears to exert pleiotropic effects on LDLC levels as well. The gene(s) influencing Lp(a) response to dietary cholesterol is not linked to the LPA locus.

Diabetes and hypertension in Mexican American families: relation to cardiovascular risk.

There is a strong familial predisposition to type 2 diabetes, hypertension, and cardiovascular disease. The authors evaluated the association between a family history of these diseases and a large panel of cardiovascular risk factors in 1,431 Mexican American subjects who were enrolled in the San Antonio Family Heart Study in San Antonio, Texas. The baseline phase of the study covered 1992-1996. Diabetes and hypertension were diagnosed according to standard clinical criteria, while cardiovascular disease was defined as a history of heart attack or heart surgery. The prevalence of diabetes, hypertension, and cardiovascular disease in this population was 15%, 12%, and 3%, respectively. For each unaffected subject, the authors computed a family history score based on the presence or absence of disease in parents and older siblings, and correlations between cardiovascular risk factors and family history scores were estimated by using likelihood-based variance component methods. Diabetes family history score was significantly correlated with a broad panel of cardiovascular risk factors, including glucose and insulin, obesity, blood pressure, triglycerides, and total cholesterol. Hypertension family history score was significantly correlated with glucose, blood pressure, body mass index, waist circumference, total cholesterol, and triglycerides. These results support the idea that genes that confer a risk for diabetes, and to a lesser extent hypertension, adversely alter the cardiovascular risk profile long before the manifestation of clinical disease.

Stability of apolipoprotein(a) isoform phenotype to postmortem conditions.

Studies, such as the one entitled Pathobiological Determinants of Atherosclerosis in Youth or PDAY, have investigated the relationship of atherosclerotic lesions with lipid and lipoprotein risk factors. However, it is possible that proteolytic hydrolysis during the postmortem period could alter protein components of lipoproteins. Apo(a) is the defining protein of Lp(a), a lipoprotein associated with risk of cardiovascular disease. Apo(a) proteins are highly polymorphic for size and we simulated, using baboon tissues, the postmortem conditions for the PDAY study in order to determine their effects on apo(a) phenotypes. The bulk of the postmortem samples (93%) were correctly phenotyped and showed little or no evidence of degradation. Thus, apo(a) isoform size phenotypes can be determined in postmortem samples, although with caution.

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.