The genetics of quantitative plasma Lp(a): analysis of a large pedigree

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Evidence for several independent genetic variants affecting lipoprotein (a) cholesterol levels

Lipoprotein (a) [Lp(a)] is an independent risk factor for atherosclerosis-related events that is under strong genetic control (heritability = 0.68-0.98). However, causal mutations and functional validation of biological pathways modulating Lp(a) metabolism are lacking. We performed a genome-wide association scan to identify genetic variants associated with Lp(a)-cholesterol levels in the Old Order Amish. We confirmed a previously known locus on chromosome 6q25-26 and found Lp(a) levels also to be significantly associated with a SNP near the APOA5-APOA4-APOC3-APOA1 gene cluster on chromosome 11q23 linked in the Amish to the APOC3 R19X null mutation. On 6q locus, we detected associations of Lp(a)-cholesterol with 118 common variants (P = 5 × 10(-8) to 3.91 × 10(-19)) spanning a ∼5.3 Mb region that included the LPA gene. To further elucidate variation within LPA, we sequenced LPA and identified two variants most strongly associated with Lp(a)-cholesterol, rs3798220 (P = 1.07 × 10(-14)) and rs10455872 (P = 1.85 × 10(-12)). We also measured copy numbers of kringle IV-2 (KIV-2) in LPA using qPCR. KIV-2 numbers were significantly associated with Lp(a)-cholesterol (P = 2.28 × 10(-9)). Conditional analyses revealed that rs3798220 and rs10455872 were associated with Lp(a)-cholesterol levels independent of each other and KIV-2 copy number. Furthermore, we determined for the first time that levels of LPA mRNA were higher in the carriers than non-carriers of rs10455872 (P = 0.0001) and were not different between carriers and non-carriers of rs3798220. Protein levels of apo(a) were higher in the carriers than non-carriers of both rs10455872 and rs3798220. In summary, we identified multiple independent genetic determinants for Lp(a)-cholesterol. These findings provide new insights into Lp(a) regulation.

The current status of lipoprotein (a) in pregnancy: a literature review

BACKGROUND AND PURPOSE

Lipoprotein (Lp) (a) is a neglected element of the blood lipid profile. It is now recognized as a determinant of coronary heart disease progression and its role in atherosclerosis and its ability to induce thrombosis make it potentially important in the course of normal and complicated pregnancies. Pregnancy involves a major transformation of metabolism to sustain fetal growth. Multiple studies have been conducted on Lp(a) in pregnancy, and it is timely to synthesize and evaluate this evidence.

METHODS AND SUBJECTS

We reviewed the MEDLINE database for all articles published concerning "lipoprotein a" and "pregnancy" from May 2003 to May 2012. A previous comprehensive review assessed the literature up to May 2003.

RESULTS

We critically analyzed 14 studies detailing the effect of complications in pregnancy on Lp(a) profile, and subsequent pregnancy outcomes where available. Studies evaluating the normal metabolic response to pregnancy, pregnancies complicated by pre-eclampsia and intra-uterine growth restriction were reviewed.

CONCLUSIONS

A substantial mass of data has accumulated describing Lp(a) changes in pregnancy. The diversity of study design limits the ability to draw broad-ranging conclusions, but brings into focus the important questions remaining, which we discuss.

Lipoprotein a levels in pediatric migraine

The purpose of this study was to examine the lipoprotein (a) [Lp(a)] levels in children with migraine to see a possible relationship between migraine and stroke via high Lp(a) levels. Plasma levels of Lp(a) were determined in 63 patients and age-matched control subjects. The mean age in the control group was 10.57 ± 3.63 years and 11.51 ± 3.19 years in the migraine patient group. The mean Lp(a) levels in control group were 10.36 ± 10.41 ng/mL and 17.09 ± 12.12 ng/mL in migraine group (P < 0.05). The median Lp(a) level in the control group was 49.38 ng/mL and was 77.62 ng/mL in the migraine group (P < 0.05). Twelve patients (19%) had Lp(a) levels of >30 ng/mL in the migraine group and 4 (6.3%) in the control group (P < 0.05). Several prothrombotic factors related to an increased risk of stroke have been studied in migraine patients. It has recently been reported that high Lp(a) concentrations represent a risk factor for migraine, thus establishing a novel plausible link between migraine and stroke. The current study suggests evidence of high Lp(a) concentrations in childhood migraine; perhaps a novel link exists between migraine and stroke.

Lipoprotein (a) [Lp(a)]: a possible link between migraine and stroke

The biologic links by which migraine may be associated with vascular events are complex, and their exact mechanisms are currently unknown. Lipoprotein(a) [Lp(a)] has been suggested to be a risk factor for stroke, but no data are available concerning its role in migraine. The purpose of this study was to examine the role of Lp(a) in influencing migraine. Plasma levels of Lp(a) have been determined in 138 patients and in 120 control subjects comparable for age and sex. Abnormal Lp(a) levels, which are defined as more than 300 mg/L, significantly influenced the predisposition to migraine after adjustment for age, sex, and vascular traditional risk factors (odds ratio [OR], 3.4; 95% confidence interval [CI], 1.57-7.55; P = 0.002). By analyzing Lp(a) concentrations according to sex, we observed a significant difference in Lp(a) 300 mg/L cutoff value between patients and controls in the female (P = 0.002) but not in the male group. Abnormal Lp(a) levels were significantly associated with migraine at multivariate analysis after adjustment for age, hypertension, and smoking habit in the female (OR, 3.88; 95% CI, 1.59-9.51; P = 0.003) but not in the male group. In all, 24 of 141 patients (17%) and 17 of 112 controls (15.2%) were postmenopausal women. By analyzing abnormal Lp(a) concentrations, no significant difference between premenopausal and postmenopausal women in both the patient and the control group was found (P = 0.4 and P = 0.6, respectively). No difference in Lp(a) concentrations was observed between patients with and without aura, and in relation to headache intensity. The current study suggested evidence of high Lp(a) concentrations affecting migraines, possibly hypothesizing a novel link between migraine and stroke.

Apolipoproteins, quantitative lipoprotein traits and multifactorial hyperlipidaemia

Genetic polymorphism and rare mutants of apolipoproteins occur in humans. The polymorphism of apolipoprotein E (apoE) is controlled by three common alleles, epsilon 2, epsilon 3, and epsilon 4, which code for proteins that differ in lipoprotein receptor binding activity, or in their catabolism in vivo, or both. This may explain the observed significant effects of the apoE alleles on the phenotypic variance of plasma lipoprotein concentrations in different ethnic groups and, moreover, the involvement of apoE alleles in the pathogenesis of multifactorial forms of hyperlipidaemia, for example, hypertriglyceridaemia, familial type III hyperlipidaemia (apoE-2 Arg-158----Cys) and polygenic hypercholesterolaemia (apoE-4 Cys-112----Arg). A further polymorphic gene locus controls the concentrations of the Lp(a) lipoprotein complex in plasma, which may vary from less than 1 mg/dl to greater than 200 mg/dl between different individuals. This lipoprotein contains two different polypeptides, apoB-100 and the Lp(a) glycoprotein. The Lp(a) glycoprotein exhibits genetic polymorphism which is controlled by a series of autosomal alleles at a single locus and which is associated with lipoprotein concentrations in plasma. This suggests that the same gene locus is involved in determining Lp(a) glycoprotein phenotypes and Lp(a) lipoprotein concentrations in plasma. Thus, there is evidence that variability in apolipoprotein genes relates to the normal variance of lipoprotein concentrations in the population and that this variability is a major genetic factor in multifactorial forms of hyperlipidaemia.

An application of a model for a genotype-dependent relationship between a concomitant (age) and a quantitative trait(LDL cholesterol)in pedigree data

In most genetic studies in humans the variability in a quantitative trait is adjusted for variability in concomitants (age, sex, etc) using a single regression equation prior to analyses of pedigree data. To illustrate an alternative approach, a single locus genetic model was tested. This model incorporates genotypic effects on the level of the trait, the variability in the trait, and the relationship between a concomitant and the trait. In this study, the model was applied to measures of age and low-density lipoprotein (LDL) cholesterol in a large kindred with familial hypercholesterolemia. The application of this model to 322 individuals in four generations provided evidence that genotypic variation at a single locus influences LDL levels early in life, the rate of increase of LDL with age and the phenotypic variance. A model with genotype-dependent slope and variance fit the data significantly better than a model with slope and variance independent of genotype. The inclusion of age-specific genotypic differences contributed to identification of high-risk individuals, to statistical support for a major locus, and to evidence for genetic determination of the tracking of LDL levels. Models that incorporate genotype-specific concomitant effects have the potential to represent more realistically the relationship between genotypic variability and quantitative phenotypic variation than models that assume that these effects do not exist.

Lipoprotein A profiles in Arab newborns

BACKGROUND

Lipoprotein A (LpA) is an intriguing lipoprotein with unquestionable genetic determination which is expressed early in life. The increasing interest in LpA is due to its established recognition as an important independent risk factor for premature atherosclerosis in cardiovascular diseases. Coronary heart disease is a major cause of morbidity and premature mortality in Kuwait. The present study was designed to measure serum LpA concentrations in Arab newborns to establish reference values for LpA in newborns and its relationship to factors present in the mother and baby.

METHODS

Serum LpA concentration was analyzed in the cord blood of 107 Arab newborns by an enzyme-linked immunosorbent assay.

RESULTS

The mean and median LpA were 54.8 mg/L and 33 mg/L, respectively (range 1-500 mg/L). The frequency distribution of LpA in cord blood was skewed to the right, with the highest frequencies of LpA below 100 mg/L. Mean LpA levels were significantly higher in female infants compared with male infants at birth (77.27 +/- 108.12 mg/L vs 40.2 +/- 41.43 mg/L, P < 0.05). Lipoprotein A concentrations in newborns were not influenced by material characteristics or type of delivery. Moreover, neonatal LpA concentration did not correlate with birthweight (BW) or body mass index (BMI).

CONCLUSIONS

Lipoprotein A concentration at birth is low and is not related to maternal characteristics. Additionally, the development of circulating LpA in serum at birth was independent of BW and BMI.

Characterization of the genetic elements controlling lipoprotein(a) concentrations in Mexican Americans. Evidence for at least three controlling elements linked to LPA, the locus encoding apolipoprotein(a)

Analyses of 1163 samples from the San Antonio Family Heart Study revealed several elements of genetic control of lipoprotein(a) (Lp(a)) concentrations in Mexican Americans. Apolipoprotein(a) (apo(a)) isoform size variation was inversely related to Lp(a) concentrations and explained about 22% of total phenotypic variation. Segregation analyses suggested the existence of a major gene that influenced an additional 41% of total Lp(a) variation. A G-->A polymorphism in the LPA promoter was in strong disequilibrium with apo(a) isoform size, but did not contribute a significant amount of additional information about Lp(a) variation. However, about 25% of variation in Lp(a) concentrations was influenced by additive polygenic effects, which include the effects of null phenotype alleles. Altogether, these genetic components explained 89% of Lp(a) variation, similar to heritability estimates made in several other studies. Apo(a) size variation and the major gene (explaining a total of about 62% of Lp(a) variation) were linked to each other and, as expected, to the plasminogen locus. Thus, together with the well-established null phenotype allele, these different genetic factors represent at least three distinct elements of control exerted at the LPA locus, which encodes the apo(a) protein.

Genetic and environmental contributions to cardiovascular risk factors in Mexican Americans. The San Antonio Family Heart Study

BACKGROUND

The familial aggregation of coronary heart disease can be in large part accounted for by a clustering of cardiovascular disease risk factors. To elucidate the determinants of cardiovascular disease, many epidemiological studies have focused on the behavioral and lifestyle determinants of these risk factors, whereas others have examined whether specific candidate genes influence quantitative variation in these phenotypes.

METHODS AND RESULTS

Among Mexican Americans from San Antonio (Tex), we quantified the relative contributions of both genetic and environmental influences to a large panel of cardiovascular risk factors, including serum levels of lipids, lipoproteins, glucose, hormones, adiposity, and blood pressure. Members of 42 extended families were studied, including 1236 first-, second-, and third-degree relatives of randomly ascertained probands and their spouses. In addition to the phenotypic assessments, information was obtained regarding usual dietary and physical activity patterns, medication use, smoking habits, alcohol consumption, and other lifestyle behaviors and medical factors. Maximum likelihood methods were used to partition the variance of each phenotype into components attributable to the measured covariates, additive genetic effects (heritability), household effects, and an unmeasured environmental residual. For the lipid and lipoprotein phenotypes, age, gender, and other environmental covariates accounted in general for < 15% of the total phenotypic variance, whereas genes accounted for 30% to 45% of the phenotypic variation. Similarly, genes accounted for 15% to 30% of the phenotypic variation in measures of glucose, hormones, adiposity, and blood pressure.

CONCLUSIONS

These results highlight the importance of considering genetic factors in studies of risk factors for cardiovascular disease.

Influence of apolipoprotein E genotypes on plasma lipid and lipoprotein concentrations: results from a segregation analysis in pedigrees with molecularly defined familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a monogenic disorder caused by mutations in the low-density lipoprotein (LDL) receptor gene. Large variations in plasma lipids and lipoprotein levels have been observed in FH families. These may be caused by other environmental and genetic factors of which apolipoprotein E (apo E) is a candidate. The possible influence of apo E polymorphism on components of variation in plasma LDL-C, triglycerides, high-density lipoprotein cholesterol (HDL-C), and lipoprotein(a) (Lp(a)) levels was investigated in 235 members of 14 families with FH. Sex-and age-adjusted mean LDL-C was influenced significantly by the apo E genotype in non-FH subjects (P <or= .01), and a similar trend was observed in FH cases. Mean plasma levels of triglyceride, HDL-C, and Lp(a) were not significantly different across the apo E genotypes in FH and in non-FH family members. Complex segregation analysis was first applied to these sex- and age-adjusted data. In addition to the major gene involved in LDL-C levels (i.e., the LDL receptor gene), there was evidence for a non-transmitted environmental major factor in addition to polygenic effect that explained the mixture of distributions in TG and a major effect in addition to polygenic loci which influenced Lp(a) levels. There was no evidence for a single major factor controlling HDL-C levels in these pedigrees. When the segregation models allowed apo E regression coefficients to be ousiotype (class) specific, the results suggested that apo E genotypes have a significant effect on LDL-C, TG, and Lp(a) levels. In conclusion, the analysis presented here supports the concept that the apo E gene has an important role in the regulation of plasma lipid and lipoproteins in FH.

Potential environmental effects on adult lipoprotein(a) levels: results from Swedish twins

Two hundred and ninety four pairs of Swedish twins reared apart and twins reared together were used to evaluate the importance of genetic and environmental influences on lipoprotein(a) (Lp(a)) levels. Lp(a) levels ranged from <10 mg/l to 926 mg/l with 7.9% of the sample having undetectable Lp(a) levels (i.e. <10 mg/l). A substantial genetic component in Lp(a) variation was indicated by a heritability estimate of approximately 90%. No difference in heritability was found across age groups. Quantitative genetic analyses also suggest correlated environmental effects most likely composed of maternal, neonatal and postnatal environmental influences. However, these effects did not reach statistical significance, partly due to a lack of power. Results from analyses of co-twin differences in Lp(a) levels for monozygotic twins indicate that sex hormone use may be of importance for Lp(a) variation in women. There was no evidence of potential influences of alcohol consumption, beta-blocker and diuretic administration on Lp(a) levels in either men or women.

Genetic effect of apolipoprotein(a) and apolipoprotein E polymorphisms on plasma quantitative risk factors for coronary heart disease in American black women

The distributions of plasma total cholesterol, apolipoproteins A-I and B and lipoprotein(a) levels as well as genetic typings of apolipoprotein(a) and apolipoprotein E were determined in a randomly selected sample of American Black women (mean age 22.2 +/- 6.5 years) . Mean plasma levels of cholesterol, apolipoprotein A-I, apolipoprotein B and lipoprotein(a) were 184.5 +/- 3.0 mg/dl, 138.0 +/- 3.1 mg/dl, 79.5 +/- 1.8 mg/dl and 24.5 +/- 1.5 mg/dl, respectively. Plasma lipoprotein (a) levels correlated significantly with apolipoprotein B and cholesterol. The contribution of apolipoprotein (a) and apolipoprotein E polymorphisms in affecting these quantitative traits was evaluated. The apolipoprotein(a) locus was extremely polymorphic with 27 alleles, while the 3 common alleles were observed in the apolipoprotein E gene. The frequencies of the APOE*2, APOE* and APOE*4 alleles were 0.094, 0.674 and 0.232, respectively. An inverse relationship was observed between the size of apolipoprotein(a) isoforms and lipoprotein(a) levels (r = 0.37; P = 0.0001). The apolipoprotein E polymorphism revealed a significant genotypic effect on apolipoprotein B (P = 0.0008) and cholesterol (P= 0.005) levels; these concentrations were lower in the APOE 2-3 genotype and higher in the 3-4 and 4-4 genotypes compared with the common 3-3 genotype. The apolipoprotein E polymorphism explained 15.8% and 6.3% of the phenotypic variance in apolipoprotein B and cholesterol levels, respectively. This study demonstrates that genetics play an important role in determining quantitative risk factors for coronary heart disease among American Black women.

C/T polymorphism in the 5' untranslated region of the apolipoprotein(a) gene introduces an upstream ATG and reduces in vitro translation

Elevated plasma levels of lipoprotein(a) [Lp(a)] are a significant-independent risk factor for arteriosclerosis. Interindividual levels of Lp(a) vary nearly 1000-fold and are mainly due to inheritance that is linked to the locus of the apolipoprotein(a) [apo(a)] gene. A search was made for sequence variants in the 5' flanking region of the apo(a) gene that affect its expression. A C to T transition at position +93 from the transcription start site was found with a frequency of 14% in the study population. In transient transfection assays in HepG2 cells, luciferase reporter gene constructs with a T at this position were associated with a 58% reduction in luciferase activity compared with the more common allele. This single base variant had no significant effect on the binding of nuclear regulatory proteins; however, it introduced an additional upstream ATG initiation codon with its own in-frame stop codon. Furthermore, equivalent levels of mRNA were produced in HepG2 cells transfected with reporter gene constructs containing either a T or a C at position +93. In vitro translation experiments using transcripts derived from either variant apo(a) promoter revealed a 60% reduction in translation associated with the T allele. Hence, the additional ATG created by the T at position +93 in the 5' flanking region of the apo(a) gene impairs the efficiency of translation from the bona fide ATG initiation codon.

Segregation analysis of plasma lipoprotein(a) levels in pedigrees with molecularly defined familial hypercholesterolemia

The role of genetic and environmental factors in determining the variability in plasma lipoprotein(a) [Lp(a)] levels was investigated in 220 members of 14 families with familial hypercholesterolemia (FH) whose plasma Lp(a) levels were previously reported [Leitersdorf et al. (1991) J Lipid Res 32:1513-1519]. One hundred four subjects harbored a mutant low density lipoprotein (LDL) receptor allele as confirmed by the identification of the specific mutations in addition to the haplotype analysis reported before. Four different mutant alleles were identified, each in a defined genetic group--Druze, Christian-Arabs, Ashkenazi, and Sepharidic Jews. Sex- and age-adjusted mean plasma Lp(a) levels were significantly higher in FH family members (34.0 mg/dl) than in non-FH family members (21.1 mg/dl). Lp(a) levels were further adjusted for lipid levels and apo(a) isoforms. A mixture of two normal distributions fitted the adjusted Lp(a) levels better than did a single normal distribution. Segregation analysis indicated that a major effect of a non-transmitted environmental factor explained the mixture of distributions in addition to polygenic loci which influenced Lp(a) levels within each distribution. The major environmental factor and the polygenic loci accounted for 45% and 20% of the adjusted Lp(a) variation, respectively. Furthermore, sex, age, lipid levels, apo(a) isoform, the major environmental effect, and the unmeasured polygenes could account for 80% of the unadjusted variation of plasma Lp(a) in these families.

Influence of apolipoprotein(a) phenotype on lipoprotein(a) quantification: evaluation of three methods

Three commercially available assays (an enzyme-linked immunosorbent assay ELISA, an immunoradiometric assay, IRMA, and a nephelometric assay) for the determination of lipoprotein(a) [Lp(a)] were compared with respect to the dependency of these assays on the various apolipoprotein(a) [apo(a)] isoforms. Although there was a strong correlation between the three methods, a significant difference between the absolute values (mg/L) was observed (p < 0.001). Using purified Lp(a) preparations, we showed that the ELISA assay quantifies the Lp(a) concentration on a molar basis, independently of the apo(a) isoform size. The IRMA and the nephelometric assay however are apo(a) isoform size dependent and overestimate the Lp(a) concentration of large apo(a) isoforms whereas the amount of small apo(a) isoforms is underestimated. In general, the isoform dependency of the Lp(a) quantification is of limited clinical relevance. In this study, inconsistent risk assignments are made in approximately 3% of the cases, when the Lp(a) concentrations obtained with the apo(a) isoform dependent assays are compared with the isoform independent ELISA.

Hypervariable polymorphism of APO(a) in blacks and whites as reflected by phenotyping

Genetic polymorphism at the apolipoprotein(a) structural locus was investigated in 203 American blacks using a high-resolution SDS-agarose electrophoresis method followed by immunoblotting, and the gene frequency data were compared with a previously screened American white sample using the same method. Between the two samples, a total of 27 discrete APO(a) allelic isoforms have been documented; of these, 24 were common to both groups. Of the 203 blacks screened, APO(a) immunoreactive isoforms were detected in 201, with a total of 101 distinct phenotypes (67 (33%) single-banded and 134 (67%) double-banded). A similar level of gene diversity was observed at the APO(a) locus in blacks (93%) and whites (94%). Despite having a similar number of alleles and a similar level of gene diversity, the frequencies of some APO(a) alleles were significantly different between blacks and whites. Overall, the frequencies of large-size APO(a) alleles, associated with lower LP(a) levels, were significantly lower (P < 0.0001), while the frequencies of medium-size APO(a) alleles, associated with intermediate LP(a) levels, were significantly higher (P < 0.0001) in blacks than in whites. However, the frequencies of small-size alleles, associated with higher LP(a) levels, were comparable between the two race groups. These data indicate that the observed differences in mean LP(a) levels between whites and blacks may be accounted for by the size variation at the APO(a) structural locus.

Apolipoprotein(a) phenotypes in cardio-cerebrovascular diseases

We report apolipoprotein(a) (apo(a)) phenotypes of 69 myocardial infarction survivors and 56 stroke patients, and compare them with those of 190 healthy Chinese. The results indicate that the distribution of apo(a) phenotype frequency in cardio-cerebrovascular disease patients is different from those of controls. The frequency of the phenotypes B, S1 and S2 in patients is remarkably higher than those in controls within the same single-band apo(a) phenotype. Moreover, the Lp(a) serum concentrations in CCVD patients are significantly higher than those in controls within the same single-band apo(a) phenotype. The apo(a) phenotype analyses of two pedigrees are shown as a typical autosomal dominant inheritance.

Epidemiology of triglycerides, small dense low-density lipoprotein, and lipoprotein(a) as risk factors for coronary heart disease

In addition to LDL cholesterol, triglyceride; small, dense LDL (LDL subclass phenotype B); and lipoprotein(a) are emerging as important risk factors for CHD. Elevated plasma levels of each of these risk factors have consistently been associated with increased risk of CHD in case-control studies of white patients. In prospective studies, however, the association between triglycerides and CHD is generally not independent of HDL cholesterol in multivariate statistical analyses. Although the data are scarce, studies in women show that triglycerides are a stronger risk factor for CHD in women than in men. Although no prospective studies of LDL subclass phenotype B have been reported, a number of potential atherogenic mechanisms may be responsible for the association with CHD seen in the case-control studies. Similarly, few prospective studies of lipoprotein(a) have been published, all in Scandinavian men. The observational studies generally show an association between elevated lipoprotein(a) and CHD in whites but not in blacks. Each of these risk factors also has a genetic component. Of the two familial forms of hypertriglyceridemia, FCH has been associated with familial CHD in two cross-sectional studies. LDL subclass phenotype B is inherited consistent with a single major gene effect, and candidate gene linkage studies are in progress to map the chromosomal location of this proposed gene. Finally, lipoprotein(a) levels are largely attributable to variation at the apo(a) locus on chromosome 6. Whether other genetic variations explain the lack of reported associations between lipoprotein(a) and CHD in black populations remains to be determined. Understanding of these "non-LDL" lipoprotein-related risk factors will provide important information for the development of new, effective intervention strategies for the prevention of CHD.

Frequent occurrence of familial aggregations of high lipoprotein(a) levels associated with small apolipoprotein(a) isoforms

School-age children with high lipoprotein(a) [Lp(a)] levels were screened and family studies were conducted to examine the relationship between high Lp(a) levels and apolipoprotein(a) [apo(a)] isoforms in families. All the probands from 17 families had one of the A2 to A12 apo(a) isoforms, which are the smaller apo(a) isoforms of the 25 different isoforms thus far detected. The ratio of subjects with high plasma Lp(a) levels was 0.47 among the first-degree relatives. All 15 relatives with high plasma Lp(a) levels shared one of the small apo(a) isoforms with the proband in each family, while 16 of 17 relatives with normal Lp(a) levels did not. These data indicate the frequent occurrence of familial aggregations of high Lp(a) levels associated with one of the small apo(a) isoforms.

Sequence polymorphisms in the apolipoprotein (a) gene. Evidence for dissociation between apolipoprotein(a) size and plasma lipoprotein(a) levels

Apolipoprotein(a) [apo(a)], an apolipoprotein unique to lipoprotein(a) [Lp(a)], is highly polymorphic in size. Previous studies have indicated that the size of the apo(a) gene tends to be inversely correlated with the plasma level of Lp(a). However, several exceptions to this general trend have been identified. Individuals with apo(a) alleles of identical size do not always have similar plasma concentrations of Lp(a). To determine if these differences in plasma Lp(a) concentrations were due to sequence variations in the apo(a) gene, we examined the sequences of apo(a) alleles in 23 individuals homozygous for same-sized apo(a) alleles. We identified four single-strand DNA conformation polymorphisms (SSCPs) in the apo(a) gene. Of the 23 homozygotes, 21 (91%) were heterozygous for at least one of the SSCPs. Analysis of a family in which a parent was homozygous for the same-sized apo(a) allele revealed that each allele, though identical size, segregated with different plasma concentrations of Lp(a). These studies indicate that the apo(a) gene is even more polymorphic in sequence than was previously appreciated, and that sequence variations at the apo(a) locus, other than the number of kringle 4 repeats, contribute to the plasma concentration of Lp(a).

Significant association between low-molecular-weight apolipoprotein(a) isoforms and intermittent claudication

The role of lipoprotein(a) (Lp[a]) and apolipoprotein(a) (apo[a]) isoforms in symptomatic peripheral atherosclerosis was studied in 100 randomly selected middle-aged (45-69 years) men with intermittent claudication (IC) and 100 randomly selected healthy control (C) subjects. IC and C subjects were matched pairwise for sex, age, and smoking habits. Plasma Lp(a) concentrations were significantly higher in IC subjects, with a median value of 20.12 mg/dl, compared with 11.11 mg/dl in C subjects (p less than 0.0009). The elevated Lp(a) concentration was to a great extent due to a significant difference in the frequency distribution of apo(a) isoforms between IC and C subjects (p less than 0.029). Low-molecular-weight apo(a) isoforms were more prevalent in IC than C subjects. Also, IC subjects with apo(a) S2 and S3 phenotypes had higher Lp(a) concentrations than control subjects with the same phenotypes: S2:60.70 mg/dl (IC) and 48.69 mg/dl (C), p less than 0.038; and S3: 30.18 mg/dl (IC) and 12.01 mg/dl (C), p less than 0.042, so other still-unknown factors, genetic or nongenetic, may be important. Stepwise logistic regression analysis demonstrated that Lp(a) concentration contributed significantly (p less than 0.0002) to IC, independent of age, smoking, hypertension, diabetes mellitus, plasma total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, apo B, and plasma total triglycerides. Apo(a) isoforms grouped according to molecular weight were also independent of the above risk factors associated (p = 0.016) with the occurrence of IC because of their low-molecular-weight but were not independent of Lp(a) concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein(a) gene accounts for greater than 90% of the variation in plasma lipoprotein(a) concentrations

Plasma lipoprotein(a) [Lp(a)], a low density lipoprotein particle with an attached apolipoprotein(a) [apo(a)], varies widely in concentration between individuals. These concentration differences are heritable and inversely related to the number of kringle 4 repeats in the apo(a) gene. To define the genetic determinants of plasma Lp(a) levels, plasma Lp(a) concentrations and apo(a) genotypes were examined in 48 nuclear Caucasian families. Apo(a) genotypes were determined using a newly developed pulsed-field gel electrophoresis method which distinguished 19 different genotypes at the apo(a) locus. The apo(a) gene itself was found to account for virtually all the genetic variability in plasma Lp(a) levels. This conclusion was reached by analyzing plasma Lp(a) levels in siblings who shared zero, one, or two apo(a) genes that were identical by descent (ibd). Siblings with both apo(a) alleles ibd (n = 72) have strikingly similar plasma Lp(a) levels (r = 0.95), whereas those who shared no apo(a) alleles (n = 52), had dissimilar concentrations (r = -0.23). The apo(a) gene was estimated to be responsible for 91% of the variance of plasma Lp(a) concentration. The number of kringle 4 repeats in the apo(a) gene accounted for 69% of the variation, and yet to be defined cis-acting sequences at the apo(a) locus accounted for the remaining 22% of the inter-individual variation in plasma Lp(a) levels. During the course of these studies we observed the de novo generation of a new apo(a) allele, an event that occurred once in 376 meioses.

Apolipoprotein(a) phenotypes, Lp(a) concentration and plasma lipid levels in relation to coronary heart disease in a Chinese population: evidence for the role of the apo(a) gene in coronary heart disease

Elevated lipoprotein(a) (Lp[a]) concentrations are associated with premature coronary heart disease (CHD). In the general population, Lp(a) levels are largely determined by alleles at the hypervariable apolipoprotein(a) (apo[a]) gene locus, but other genetic and environmental factors also affect plasma Lp(a) levels. In addition, Lp(a) has been hypothesized to be an acute phase protein. It is therefore unclear whether the association of Lp(a) concentrations with CHD is primary in nature. We have analyzed apo(a) phenotypes, Lp(a) levels, total cholesterol, and HDL-cholesterol in patients with CHD, and in controls from the general population. Both samples were Chinese individuals residing in Singapore. Lp(a) concentrations were significantly higher in the patients than in the population (mean 20.7 +/- 23.9 mg/dl vs 8.9 +/- 12.9 mg/dl). Apo(a) isoforms associated with high Lp(a) levels (B, S1, S2) were significantly more frequent in the CHD patients than in the population sample (15.9% vs 8.5%, P less than 0.01). Higher Lp(a) concentrations in the patients were in part explained by this difference in apo(a) allele frequencies. Results from stepwise logistic regression analysis indicate that apo(a) type was a significant predictor of CHD, independent of total cholesterol and HDL cholesterol, but not independent of Lp(a) levels. The data demonstrate that alleles at the apo(a) locus determine the risk for CHD through their effects on Lp(a) levels, and firmly establish the role of Lp(a) as a primary genetic risk factor for CHD.

Lipoprotein(a) at birth, in blacks and whites

It has been shown that blacks have considerably higher concentrations than whites of lipoprotein(a) (Lp(a)), which has been identified as an independent risk factor for coronary heart disease, vein graft restenosis, and cerebrovascular disease. Smaller differences in Lp(a) concentrations have been noted between males and females. To examine whether gender and race differences are already detectable at birth, we examined Lp(a) concentrations in cord blood samples of 109 black (49 male and 60 female) and 123 white (67 male and 56 female) newborns. Maternal age, gestational age, fetal maturity indicators, weight, height and head circumference were analyzed as covariates. For race and sex combined, the mean Lp(a) concentration was 4.0 mg/dl (S.D. of 3.94 mg/dl), approximately 5-fold lower than that observed in adults. No statistically significant differences were found between race or gender groups. The cross-sectional examination of serum Lp(a) concentrations of 221 infants, children and adults showed a gradual increase in Lp(a) concentrations from birth to adult values by the second year of life. We conclude that the system responsible for the production and control of Lp(a) concentration is not yet mature--or has not yet been challenged--at birth.

Racial (black-white) differences in serum lipoprotein (a) distribution and its relation to parental myocardial infarction in children. Bogalusa Heart Study

BACKGROUND

The value of lipoprotein (a) [Lp(a)] in the prediction of coronary artery disease risk very early in life remains to be established in different racial groups.

METHODS AND RESULTS

Serum Lp(a) distribution and its relation to parental histories of myocardial infarction were examined in 2,438 children (8-17 years old) from a biracial community. Parental myocardial infarction was used as a surrogate measure of future risk of disease in the offspring. Lp(a) levels averaged 1.7-fold higher in blacks than in whites (p less than 0.0001). A small but significant sex difference (females greater than males, p less than 0.05) was seen in both races. Race was the only independent variable that contributed appreciably (9%) to the variability of Lp(a) in serum. White children with parental myocardial infarction (n = 90) had increased levels of Lp(a) compared with those without parental myocardial infarction (22.4 versus 17.1 mg/dl, p less than 0.01). Furthermore, among white children, the prevalence of parental myocardial infarction was higher in those with Lp(a) levels of more than 25 mg/dl than in those with values of 25 mg/dl or less (9.5% versus 5.4%, p less than 0.01). In contrast, the relation of Lp(a) to parental myocardial infarction was not seen in black children. No associations were observed between parental myocardial infarction and serum levels of any of the lipids or lipoprotein cholesterol classes in children of either race.

CONCLUSIONS

Serum Lp(a) levels may prove valuable in the assessment of coronary artery disease risk early in life among white populations. These findings also emphasize the need to evaluate the atherogenic potential of Lp(a) in different racial groups.

Molecular basis of apolipoprotein (a) isoform size heterogeneity as revealed by pulsed-field gel electrophoresis

Lipoprotein(a) [Lp(a)] is a cholesterol-rich lipoprotein that is distinguished by its content of a glycoprotein called apolipoprotein(a) [apo(a)]. Apo(a) varies in size among individuals owing to different numbers of cysteine-rich sequences that are homologous to kringle 4 of plasminogen. The genetic basis for this variation is not understood at the genomic level. In this study we used pulsed-field gel electrophoresis and genomic blotting to identify a highly polymorphic restriction fragment from the apo(a) gene. The fragment contains multiple tandem repeats of a kringle 4-encoding sequence and varies in length from 48 to 190 kb depending on the number of kringle 4-encoding sequences. A total of 19 different alleles were identified among 102 unrelated Caucasian Americans. 94% of individuals studied had two different alleles which could be distinguished by size on pulsed-field gel electrophoresis. The degree of size heterogeneity was much greater than had been previously appreciated based on the analysis of the apparent molecular mass of the protein. The size of the apo(a) gene correlated directly with the size of the apo(a) protein, and inversely with the concentration of Lp(a) in plasma. Segregation analysis of the apo(a) gene was performed in families; siblings with identical apo(a) genotypes had similar plasma levels of Lp(a). These results suggest that in the normal population, the level of plasma Lp(a) is largely determined by alleles at the apo(a) locus.

Effects of the apolipoprotein(a) size polymorphism on the lipoprotein(a) concentration in 7 ethnic groups

Apolipoprotein(a) [apo(a)] exhibits a genetic size polymorphism explaining about 40% of the variability in lipoprotein(a) [Lp(a)] concentration in Tyroleans. Lp(a) concentrations and apo(a) phenotypes were determined in 7 ethnic groups (Tyrolean, Icelandic, Hungarian, Malay, Chinese, Indian, Black Sudanese) and the effects of the apo(a) size polymorphism on Lp(a) levels were estimated in each group. Average Lp(a) concentrations were highly significantly different among these populations, with the Chinese (7.0 mg/dl) having the lowest and the Sudanese (46 mg/dl) the highest levels. Apo(a) phenotype and derived apo(a) allele frequencies were also significantly different among the populations. Apo(a) isoform effects on Lp(a) levels were not significantly different among populations. Lp(a) levels were however roughly twice as high in the same phenotypes in the Indians, and several times as high in the Sudanese, compared with Caucasians. The size variation of apo(a) explains from 0.77 (Malays) to only 0.19 (Sudanese) of the total variability in Lp(a) levels. Together these data show (I) that there is considerable heterogeneity of the Lp(a) polymorphism among populations, (II) that differences in apo(a) allele frequencies alone do not explain the differences in Lp(a) levels among populations and (III) that in some populations, e.g. Sudanese Blacks, Lp(a) levels are mainly determined by factors that are different from the apo(a) size polymorphism.

The mysteries of lipoprotein(a)

Lipoprotein(a) [Lp(a)] is a macromolecular complex found in human plasma that combines structural elements from the lipoprotein and blood clotting systems and that is associated with premature coronary heart disease and stroke. It is assembled from low-density lipoprotein (LDL) and a large hydrophilic glycoprotein called apolipoprotein(a) [apo(a)], which is homologous to the protease zymogen plasminogen. Plasma Lp(a) concentrations vary 1000-fold between individuals and represent a continuous quantitative genetic trait with a skewed distribution in Caucasian populations. Variation in the hypervariable apo(a) gene on chromosome 6q2.6-q2.7 and interaction of apo(a) alleles with defective LDL-receptor genes explain a large fraction of the variability of plasma Lp(a) concentrations. Though of high theoretical and practical interest, many aspects of the metabolism, function, evolution, and regulation of plasma concentrations of Lp(a) are presently unknown, controversial, or mysterious.

The hyperlipoproteinemias

The association of disturbances of plasma lipid transport and atherogenesis has been recognized, and scientific data continue to accumulate to explain this association from a mechanistic viewpoint. A number of recent clinical trials have shown that cholesterol-lowering therapy can prevent the complications of atherosclerosis. Consequently, the attention of physicians to therapeutic intervention has increased and public awareness to plasma cholesterol levels has been heightened. This article summarizes current knowledge of how plasma lipid transport is regulated. The classical primary hyperlipoproteinemias are considered and hyperlipoproteinemias occurring secondary to other diseases are discussed. Standard methods to diagnose the defined genetic hyperlipidemias are outlined, and new approaches to assess risk of atherosclerosis are examined. Finally, the role of dietary measures and drugs in lowering blood lipids and reducing risk of coronary heart disease is delineated.

The gene for the Lp(a)-specific glycoprotein is closely linked to the gene for plasminogen on chromosome 6

We have studied the segregation of the Lp(a) glycoprotein phenotypes and of the plasminogen (PLG) polymorphism in three two-generation families. The inheritance of the Lp(a) gene was followed using the Lp(a) glycoprotein size polymorphism and that of the plasminogen gene, using protein and DNA polymorphisms. In the three families studied, no recombination was observed in 18 meioses. The lod score for linkage between the Lp(a) glycoprotein locus and the plasminogen locus in these families is greater than 5.0 at a recombination fraction of theta = 0. Our results show that the structural gene for the Lp(a) glycoprotein is closely linked to the gene for plasminogen on chromosome 6.

Immunochemical characterization and quantitation of lipoprotein (a) in baboons. Development of an assay depending on two antigenically distinct proteins

We have raised specific antibodies against the protein component of baboon lipoprotein (a) (Lp(a]. Apolipoprotein (apo) Lp(a) is a very large protein which separates into two distinct proteins, apo B and apo (a), when 2-mercaptoethanol is included during sample treatment for sodium dodecyl sulfate-electrophoresis. The antibodies were specific for baboon apo (a) and apo B. The presence of the two distinct antigens in the lipoprotein permitted the development of an enzyme-linked immunosorbent assay that was specific for Lp(a) particles in serum. The assay could detect less than 1 ng of Lp(a) protein per well and was useful in the range of 1-9 ng. The assay was specific for Lp(a) and did not respond to other lipoproteins, such as low density lipoprotein. Lp(a) could be accurately quantitated in serum frozen at -80 degrees C in plastic tubing segments. Using the Lp(a) assay, the mean serum level of 80 unrelated baboons was 4.7 mg/dl, with the distribution skewed toward the lower levels. These data further support the value of the baboon as a model of the atherogenic lipoprotein Lp(a).

Lp(a) phenotyping by immunoblotting with polyclonal and monoclonal antibodies

A new method that allows rapid phenotyping of genetic Lp(a) glycoprotein types in large numbers of samples is described. The method is based on sodium dodecyl sulfate gel electrophoresis of reduced serum or plasma in horizontal slab gels followed by immunoblotting with polyclonal anti-Lp(a) lipoprotein or monoclonal anti-Lp(a) glycoprotein antibodies. Phenotyping of 194 unrelated, healthy subjects resulted in Lp(a) allele frequencies of Lp(a)B = 0.013, Lp(a)S1 = 0.032, Lp(a)S2 = 0.106, Lp(a)S3 = 0.096, Lp(a)S4 = 0.156, and Lp(a)O = 0.600, and confirmed the recently recognized association of Lp(a) glycoprotein phenotype with Lp(a) lipoprotein concentration. The new procedure is suitable for large-scale population, genetic, and epidemiologic studies and may be important for atherosclerotic risk assessment.

Genetics of the quantitative Lp(a) lipoprotein trait. II. Inheritance of Lp(a) glycoprotein phenotypes

Lp(a) glycoprotein exhibits an apparent size polymorphism that is associated with genetically controlled Lp(a) lipoprotein concentrations in plasma (Utermann et al. 1988). We have tested the hypothesis that this polymorphism is genetically controlled by studying 15 matings with a total of 44 offspring. This confirmed our conclusion that Lp(a) types are controlled by a series of codominant alleles LpF, LpB, LpS1, LpS2, LpS3 and LpS4 and by a null allele LpO. Together with the data from the accompanying paper this indicates that the structural gene for the Lp(a) protein is the major gene locus determining Lp(a) lipoprotein concentrations in plasma.

Genetics of the quantitative Lp(a) lipoprotein trait. I. Relation of LP(a) glycoprotein phenotypes to Lp(a) lipoprotein concentrations in plasma

The Lp(a) lipoprotein is a complex particle composed of a low density lipoprotein (LDL)-like lipoprotein and the disulfide bonded Lp(a) glycoprotein. The complex represents a quantitative genetic trait. SDS gel electrophoresis under reducing conditions of sera followed by immunoblotting with affinity-purified polyclonal anti-Lp(a) demonstrated inter- and intra-individual size heterogeneity of the glycoprotein with apparent Mr in the range 400-700kDa. According to their relative mobilities compared to apo B-100 the Lp(a) patterns were categorized into phenotypes F, B, S1, S2, S3 und S4 and into the respective double-band phenotypes. This size heterogeneity seems to be controlled by multiple alleles designated LpF, LpB, LpS1, LpS2, LpS3, LpS4 and a null allele (LpO) at a single locus. Phenotype frequencies observed in 441 unrelated subjects were in good agreement with those expected from the genetic hypothesis. Comparison of Lp(a) lipoprotein concentrations in the different phenotypes revealed a highly significant association of phenotypes B, S1 and S2 with high, and phenotypes S3 und S4 with intermediate Lp(a) concentrations. A third mode is represented by the null phenotype were no Lp(a) band is detected upon immunoblotting and Lp(a) lipoprotein is low or absent. We conclude that the same gene locus is involved in determining Lp(a) glycoprotein phenotype and Lp(a) lipoprotein concentrations in plasma. This major gene seems to be the Lp(a) glycoprotein structural gene locus.

Recruitment of members of high-risk Utah pedigrees

Cardiovascular Genetics Research Projects in Utah are designed to investigate genetic and environmental determinants of early coronary disease, stroke, and hypertension in population-based pedigrees. Early coronary disease is defined as the occurrence of documented coronary death or myocardial infarction before age 55. Detailed recruitment experience is reported for 2500 persons age 3-83 years in 98 high-risk pedigrees from three ascertainment groups: 1. Descendants of sibships with two or more stroke deaths before age 75. 2. Descendants of sibships with two or more coronary deaths before age 55. 3. First- and second-degree relatives of hypertensive and normotensive probands randomly selected from the Utah Hypertension Detection and Follow-up Program. A response rate of 94% of invited adults attending the first 4-hour clinic visit for detailed screening in 1980-1983 was achieved by multiple telephone, mail, and personal contacts and rescheduling of missed clinic appointments. For the same participants, a second screening cycle in 1983-1986 showed a 91% response of invited adults. Second visit response rates were examined within subgroups according to data collected at the first clinic visit. Below average response rates included 79% of persons with fewer than 12 years of education, 84% of current smokers, and 86% of divorced persons. Above average response rates included 93% of persons attending college and 95% of persons with total family income above $25,000. There were no differences in response according to sex or age. The average cost of recruitment was $59 per person and represented about 10% of the total budget for the High-Risk Pedigree Project.

Lp(a) glycoprotein phenotypes. Inheritance and relation to Lp(a)-lipoprotein concentrations in plasma

The Lp(a) lipoprotein represents a quantitative genetic trait. It contains two different polypeptide chains, the Lp(a) glycoprotein and apo B-100. We have demonstrated the Lp(a) glycoprotein directly in human sera by sodium dodecyl sulfate-gel electrophoresis under reducing conditions after immunoblotting using anti-Lp(a) serum and have observed inter- and intraindividual size heterogeneity of the glycoprotein with apparent molecular weights ranging from approximately 400,000-700,000 D. According to their relative mobilities compared with apo B-100 Lp(a) patterns were categorized into phenotypes F (faster than apo B-100), B (similar to apo B-100), S1, S2, S3, and S4 (all slower than apo B-100), and into the respective double-band phenotypes. Results from neuraminidase treatment of isolated Lp(a) glycoprotein indicate that the phenotypic differences do not reside in the sialic acid moiety of the glycoprotein. Family studies are compatible with the concept that Lp(a) glycoprotein phenotypes are controlled by a series of autosomal alleles (Lp[a]F, Lp[a]B, Lp[a]S1, Lp[a]S2, Lp[a]S3, Lp[a]S4, and Lp[a]0) at a single locus. Comparison of Lp(a) plasma concentrations in different phenotypes revealed a highly significant association of phenotype with concentration. Phenotypes B, S1, and S2 are associated with high and phenotypes S3 and S4 with low Lp(a) concentrations. This suggests that the same gene locus is involved in determining Lp(a) glycoprotein phenotypes and Lp(a) lipoprotein concentrations in plasma and is the first indication for structural differences underlying the quantitative genetic Lp(a)-trait.

A re-examination of major locus hypotheses for high density lipoprotein cholesterol level using 2,170 persons screened in 55 Utah pedigrees

A dominant major locus (allele frequency of .0025 +/- .0014), resulting in low levels of high density lipoprotein cholesterol (HDL-C), was revealed by likelihood analysis on 2,170 persons in 55 Utah pedigrees. This allele was expressed through HDL-C levels ranging from 20 to 30 mg/dl in seven persons in two pedigrees. Early coronary heart disease was associated with the allele in one pedigree, but not in the other. In the pedigree without associated heart disease, HDL subfractions HDL2 and HDL3 were both low in individuals with the low HDL-C allele. No other major locus determining either high or low levels of HDL-C was identified in our sample. Polygenic heritability as part of the mixed model was estimated as .561 +/- .035.

Effects of household sharing on high density lipoprotein and its subfractions

Household effects accounted for significant proportions of the observed variance of high density lipoprotein cholesterol (HDL-C) and subfractions HDL2 and HDL3. It was found that 19.3% of HDL-C variance could be attributed to a juvenile sib effect (under age 18); 17.4% of HDL2 variance could be attributed to a sib effect (of any age); and 22.1% and 32.6% of the HDL3 variance could be attributed to a parent-offspring effect and a sib effect (of any age), respectively. In addition, additive genetic effects accounted for 56.5%, 37.3%, and 28.3% of the variances of HDL-C, HDL2, and HDL3, respectively. These are maximum likelihood estimates obtained using a variance components model on 2,149 HDL-C levels measured on members of 54 Utah pedigrees, and 337 HDL2 and HDL3 levels measured on a subset of 14 pedigrees.

Genetics of the Lp lipoprotein in Japanese-Americans

Segregation analysis of four Lp assays on 557 children in 227 families reveals a dominant major gene and a residual heritable component that may reflect one or more alleles of weaker effect. Close or moderate linkage to esterase-D (ESD) is excluded.