Cultural and biological inheritance of plasma lipids

Genetic and environmental determinants for lipoprotein concentrations in blood

Path and segregation analyses have been performed on cholesterol and triglyceride contents of serum as well as on very low, low and high density lipoproteins in 78 Swedish nuclear families. The effect of environmental variables like alcohol and smoking on the concentrations of the different lipoproteins has been studied. Genetic heritability was 0.16-0.68 for the cholesterol fractions and 0-0.56 for the triglyceride fractions. No major gene was evident for any of the variables studied.

Variance decomposition of apolipoproteins and lipids in Danish twins

OBJECTIVE

Twin studies are used extensively to decompose the variance of a trait, mainly to estimate the heritability of the trait. A second purpose of such studies is to estimate to what extent the non-genetic variance is shared or specific to individuals. To a lesser extent the twin studies have been used in bivariate or multivariate analysis to elucidate common genetic factors to two or more traits.

METHODS AND RESULTS

In the present study the variances of traits related to lipid metabolism is decomposed in a relatively large Danish twin population, including bivariate analysis to detect possible common genetic factors of the traits.

CONCLUSIONS

The heritabilities of apolipoprotein B and E, cholesterol, LDL, and high density lipoprotein (HDL) were significant in the general population, although gender-specific levels and significance were detected. Heritabilities of apolipoprotein A1, triglycerides, and very low density protein (VLDL) were only significant when the population was stratified according to gender.

Genetic and environmental effects on coronary heart disease risk factors in northern Norway. The cardiovascular disease study in Finnmark

This study comprised 1377 first degree relatives in 575 families ascertained through a comprehensive screening of the general population from 20 to 52 years of age. Path analysis using parsimonious models gave evidence of significant biologic and environmental transmission for total cholesterol (genetic and cultural heritabilities were 0.46 and 0.05, respectively), high density lipoprotein cholesterol (0.42, 0.10), triglycerides (0.21, 0.07), and systolic (0.48, 0.04) and diastolic (0.35, 0.05) blood pressure. Compared with other studies employing the same path analytic model, heritability estimates in general were among the highest reported, except for the somewhat lower genetic component in total cholesterol and triglycerides. For the first time in a single sample from the general population, lipid and blood pressure variables were investigated applying the same methodology, and good agreement was illustrated by the result that identical parsimonious models were reached for all phenotypes, with the exception of a single additional parameter for total cholesterol. About one fourth to one half of the total phenotypic variance could be ascribed to genetic sources, whereas the contribution from shared familial environment was much smaller.

Genetic estimates for plasma lipids and lipoproteins in cynomolgus monkeys under assortative mating

Data obtained from cynomolgus monkeys selected for total plasma cholesterol (TPC) response to dietary cholesterol and nonselected controls were used to estimate heritability of TPC and lipoprotein concentrations. A total of 345 observations were collected on 57 progeny from 18 sires. Heritability estimates obtained by a paternal half-sib analysis and by regression of offspring on mid-parent values were 0.45 +/- 0.24 and 0.69 +/- 0.18 for TPC, 0.63 +/- 0.30 and 0.64 +/- 0.17 for LDLC, and 0.80 +/- 0.36 and 0.59 +/- 0.14 for HDLC, respectively. These results suggest that TPC and lipoprotein concentrations are influenced by additive genetic effects in cynomolgus monkeys, establishing their importance as an animal model for studying the genetics of lipoproteins.

Path analysis of familial resemblance of pulmonary function and cigarette smoking

The techniques of path analysis were utilized to assess the relative importance of genetic factors, personal smoking behavior, and shared environment in the resemblance of pulmonary function among relatives using both cross-sectional and longitudinal data from nuclear families. Data on 1-s forced expiratory volume, FEV1 (adjusted for age, sex, race, height, and ascertainment group) and the number of cigarettes smoked per day were available on 978 individuals in 384 nuclear families residing in the Baltimore metropolitan area. All these individuals were seen twice between 1971 and 1981, with an average of 5 yr between visits. The direct effect of an individual's own smoking explained 10 and 3% of variation in adjusted FEV1 among parents and offspring, respectively. Shared environmental factors influencing personal smoking behavior accounted for 5% of the parent-offspring correlation in adjusted FEV1 and 3% of the sibling correlation in adjusted FEV1 in this sample. Undefined environmental factors that influenced an individual's smoking habits and could be shared among relatives were found to explain 19% of the familial correlations in smoking. Genetic heritability estimates ranged between 36 and 40%, with no evidence of intergenerational differences in the expression of apparent genetic control of pulmonary function.

Genetic and environmental determinants of serum lipids and lipoproteins in French Canadian families

The contribution of genetic and environmental factors in serum triglycerides (TG), total cholesterol (CHOL), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), and HDL-C/CHOL ratio were studied in 1630 subjects from 375 families of French descent by using a path analysis procedure. Familial correlations were computed in several pairs of biological relatives and relatives by adoption after adjustment for age and gender effects and after further adjustment for physical fitness, level of habitual physical activity, total body fat and fat distribution, diet, smoking, and alcohol consumption. The model of path analysis allowed the separation of transmissible variance (t2) into genetic (h2) and cultural (b2) components of inheritance. Under the most parsimonious solution and after adjustment for age, gender, and concomitants, the transmissible variance was entirely accounted for by genetic factors (t2 = h2), with h2 estimates of 0.52, 0.55, 0.60, and 0.63 for TG, CHOL, LDL-C, HDL-C, and HDL-C/CHOL, respectively. These estimates were similar to those obtained after adjustment for age and gender effects only. The contribution of nontransmissible environmental factors ranged from 0.48 for TG to 0.37 for HDL-C/CHOL ratio. These results suggest that both genetic and environmental factors contribute to the variation in blood lipids and lipoproteins in this population and that nongenetic influences are not associated with cultural factors transmitted across generations.

Use of robust variance components models to analyse triglyceride data in families

A robust approach for analysis of variance components models is presented which does not rely on the assumption of multivariate normality for its validity. This approach uses the multivariated normal distribution as a 'working model' but obtains standard errors for the final estimators which do not depend on this underlying distribution. By using the observed variance in the first derivatives of the multivariate normal 'working model' to modify the conventional score test, hypotheses regarding specific components can also be tested without relying directly on the assumption of multivariate normality. A special case is presented where both the modified score test and the likelihood ratio test are equally robust, and simulated data are used to illustrate this situation. Measurements of triglyceride levels in 391 individuals in 60 families randomly selected from the membership of a health maintenance organization are used to illustrate this robust approach to variance components.

The Collaborative Lipid Research Clinics Family Study: biological and cultural determinants of familial resemblance for plasma lipids and lipoproteins

This paper reports on the biological and cultural determinants of total, LDL, and HDL cholesterol, and triglyceride (TC, LDL-C, HDL-C, TG) levels using a general linear model on randomly selected family data collected during 1975-1978 at nine North American Lipid Research Clinics. Initially, the analyses were clinic-specific to assess the importance of genetic and cultural transmission, marital resemblance, and other determinants of these traits and then were made jointly to identify the nature and sources of any heterogeneity between clinics. There was evidence of significant genetic and cultural factors for all traits in most clinics. Clinic heterogeneity was also significant, but excluding one clinic reduced the heterogeneity considerably. The genetic (h2) and cultural (c2) heritabilities for the remaining eight clinics were homogeneous with pooled estimates of h2 of .556 +/- .028, .539 +/- .028, .485 +/- .029, and .358 +/- .028, and of c2 of .029 +/- .006, .033 +/- .006, .075 +/- .008, and .089 +/- .009 for TC, LDL-C, HDL-C, and TG, respectively. Among the traits, HDL-C exhibited the most difference among clinics, and both HDL-C and TG showed the largest cultural heritability. The relevance of these and similar studies in a broader understanding of the determinants of plasma lipids and lipoproteins is discussed.