Biochemical, clinical, genetic and metabolic studies of hyperapo-beta-lipoproteinaemia

Hereditary dyslipidemias and combined risk factors in children with a family history of premature coronary artery disease

AIM

Schoolchildren aged 10-11 with a family history of premature coronary artery disease (CAD), were examined in order to identify children with genetically determined dyslipidemias and a combination of risk factors.

METHODS

A total of 4000 questionnaires were distributed by the school; 55% of the families answered and returned the questionnaire. Blood lipids, apolipoprotein B, and Lp(a) lipoprotein were analysed in high risk children and their parents.

RESULTS

A family history of premature CAD in parents or grandparents was identified in 208 families; 175 agreed to take part in a clinical examination and laboratory tests. Normal blood lipid tests were found in 89 children. Another 48 had an isolated increase of Lp(a) lipoprotein of minor clinical importance. Of the remaining 38 children, 23 had non-hereditary abnormalities of low (LDL) or high density lipoprotein (HDL) cholesterol or apolipoprotein B. Fifteen children were suspected to have genetically determined dyslipidemias or a combination of risk factors: in four, possible familial hypercholesterolaemia (FH); in five, possible familial combined hyperlipidaemia; in three, hereditary low HDL cholesterol; and in three a combination of high LDL cholesterol and Lp(a) lipoprotein concentrations. In addition, possible FH was detected in eight of the parents.

CONCLUSION

It is worthwhile asking parents about the occurrence of premature CAD among their child's closest relatives.

Influence of triglyceride concentration on the relationship between lipoprotein cholesterol and apolipoprotein B and A-I levels

A sample of 2,103 men aged 47 to 76 years from the Québec Cardiovascular Study cohort was examined to quantify the influence of plasma triglyceride (TG) levels on the relationship between plasma lipoprotein cholesterol and either apolipoprotein A-I (apo A-I) or apo B concentrations. Regression analyses between high-density lipoprotein cholesterol (HDL-C) and apo A-I through TG tertiles showed highly significant correlations (.62 < or = r < or = .75, P < .0001) in all TG tertiles between these 2 variables. The associations for plasma apo B versus low-density lipoprotein cholesterol (LDL-C) and non-HDL-C levels were also studied on the basis of TG concentrations, and correlation coefficients between either LDL-C or non-HDL-C and apo B were essentially similar among TG tertiles (.78 < or = r < or = .85 and .83 < or = r < or = .86 for LDL-C and non-HDL-C, respectively, P < .0001). Regression analyses also showed that lower HDL-C levels were found for any given apo A-I concentration among men in the 2 upper TG tertiles, whereas lower LDL-C concentrations were observed at any given apo B level among subjects in the upper TG tertile. We further investigated whether there were synergistic alterations in the HDL-C/apo A-I and LDL-C/apo B ratios as a function of increasing plasma TG. A significant association was noted between these 2 ratios (r = .37; P < .0001). Mean HDL-C/apo A-I and LDL-C/apo B ratios were then calculated across quintiles of plasma TG concentrations. Increased TG concentrations were first associated with a reduced HDL-C/apo A-I ratio, followed by a decreased LDL-C/apo B ratio. These results suggest that a relatively modest increase in TG may rapidly alter the relative cholesterol content of HDL particles. Finally, the cholesterol content of the non-HDL fraction appears to be influenced less by TG levels than HDL-C and LDL-C fractions. Thus, the plasma apo B-containing lipoprotein cholesterol level may provide a better index of number of atherogenic particles than the LDL-C concentration, particularly in the presence of hypertriglyceridemia (HTG).

Familial combined hyperlipidemia in children: clinical expression, metabolic defects, and management

The first evidence that elevation of plasma levels of cholesterol is a risk factor for the development of atherosclerosis in children came from the Bogalusa Heart Study in 1986, which reported an association between aortic fatty streaks in 3- to 26-year-old subjects and increased plasma levels of low-density lipoprotein cholesterol (LDL-C). The most compelling evidence of a cause-and-effect relationship has come from the multicenter cooperative study called the Pathobiological Determinants of Atherosclerosis in Youth. When the investigators examined the abdominal aorta and the right coronary artery of adolescents and young adults who had died of trauma, they found a significant relationship between the sum of the very low density lipoprotein (VLDL) plus LDL-C level and both fatty streaks and raised atherosclerotic lesions. They also found an inverse relationship between those lesions and increased high-density lipoprotein cholesterol (HDL-C) levels. In addition, their studies showed that smoking (as assessed by the serum thiocyanate level) promotes atherogenesis in children as young as age 15 years. Thus many pediatricians have now accepted the importance of identifying children with significant hypercholesterolemia so that appropriate dietary and life-style modifications can be recommended. This is especially important because there is often a major genetic component to the hyperlipidemia seen in children.

Serum lipoprotein(a) in healthy Japanese children 5 years of age

Serum lipoprotein(a) [Lp(a)] concentrations were investigated in 155 Japanese children aged 5 years. The frequency distribution of Lp(a) concentrations was highly skewed and ranged from 1 to 109 mg/dL. The mean and median values of Lp(a) were 16.5 mg/dL (s.d. 17.3 mg/dL) and 12 mg/dL. The incidence of Lp(a) concentrations > or = 30 mg/dL was significantly high in children with total cholesterol > or = 200 mg/dL, not including the case of familial hypercholesterolaemia. Log Lp(a) values showed an inverse correlation with bodyweight and body mass index. No significant differences in Lp(a) levels could be seen between the groups according to the presence or absence of coronary heart disease and cerebral vascular accident in family histories. The results suggest that Lp(a) in Japanese children aged 5 years was essentially the same as that in adults. Further study may be needed to disclose the factors that influence Lp(a) concentration in childhood.

Familial combined hyperlipidemia in children: clinical expression, metabolic defects, and management

Familial combined hyperlipidemia (FCHL) is a dominantly inherited hyperlipidemia that occurs in at least 1% of the adult population and is responsible for 10% of premature coronary artery disease. In families referred for evaluation because of primary hyperlipidemia in a child, FCHL is expressed three times more commonly than familial hypercholesterolemia and half of the siblings are affected. Several metabolic defects apparently are associated with the FCHL phenotype. Most commonly, excess production of very low density lipoprotein apolipoprotein B can be demonstrated. In other families, reduced lipoprotein lipase activity is associated. One allele at a locus influencing apolipoprotein B levels predicts FCHL in a large proportion of families ascertained through affected children. Whether this allele is responsible for the excess of very low density lipoprotein apolipoprotein B detected in metabolic studies has not been elucidated. Management of FCHL in children begins with dietary modification. A bile acid sequestrant may be considered as well if diet cannot reduce the plasma low-density lipoprotein cholesterol level to less than 4.13 mmol/L (160 mg/dl) after the age of 10 years. Although the hydroxymethylglutaryl-coenzyme A reductase inhibitors are not currently recommended for children younger than 19 years of age, we speculate that they will be increasingly utilized for the management of FCHL in teenage boys who continue to have low density lipoprotein cholesterol levels greater than 4.13 mmol/L (160 mg/dl) after dietary modification.

Hypertriglyceridemia: risks and perspectives

The evidence linking hypertriglyceridemia and coronary artery disease (CAD) is reviewed. A positive correlation between plasma triglyceride level and CAD incidence has been demonstrated in most prospective studies on univariate analysis. However, the significance is weakened on multivariate analysis, in particular when level of high-density lipoprotein (HDL) cholesterol is taken into account, perhaps because of the close metabolic interrelation between the triglyceride-rich lipoproteins and HDL particles. Recent analyses of clinical data have shown that the combination of elevations of low-density lipoprotein cholesterol and triglyceride and low levels of HDL cholesterol confers particularly high risk for CAD. The U.S. National Institutes of Health Consensus Development Conference on Triglyceride, High Density Lipoprotein, and Coronary Heart Disease in February 1992 made recommendations to integrate more fully HDL cholesterol and triglyceride levels into the assessment and treatment of dyslipidemia and CAD risk. Treatment of hypertriglyceridemia should focus on diet and weight control, exercise, and smoking cessation, as well as control of other major risk factors for CAD, notably hypercholesterolemia and hypertension.

Long-term predictors of subsequent cardiovascular events with coronary artery disease and 'desirable' levels of plasma total cholesterol

BACKGROUND

Patients with coronary artery disease (CAD) are at considerable risk for subsequent cardiovascular events. Although hyperlipidemia accentuates the risk, predictors of subsequent events with CAD and desirable total cholesterol (TC) (less than 5.2 mmol/l) have not been assessed.

METHODS AND RESULTS

A survival analysis was performed in a subset of 740 consecutive patients who underwent diagnostic coronary arteriography between 1977 and 1978. Eight-three men and 24 women with angiographically documented CAD and desirable TC were followed for subsequent cardiovascular events, including myocardial infarction and cardiovascular death. Over a 13-year period, 75% of CAD subjects with reduced high density lipoprotein cholesterol (HDL-C) (less than 0.9 mmol/l) developed a subsequent cardiovascular event compared with 45% of those with HDL-C greater than or equal to 0.9 mmol/l (p = 0.002). A Kaplan-Meier analysis revealed significantly greater survival from cardiovascular end points in patients with baseline levels of HDL-C greater than or equal to 0.9 mmol/l (p = 0.005). After 11 variables were tested, an age-adjusted Cox proportional-hazards model identified two pairs of independent predictors of subsequent cardiovascular events: they were a left ventricular ejection fraction (LVEF) less than 35% (relative risk [RR], 6.5; 95% confidence interval [CI], 2.8, 15.3; p less than 0.001) and reduced HDL-C (RR, 2.0; 95% CI, 1.2, 3.3; p = 0.01) in the first model and LVEF less than 35% (RR, 6.5; 95% CI, 2.7, 15.6; p less than 0.001) and TC:HDL ratio greater than or equal to 5.5 (RR, 1.9; 95% CI, 1.1, 3.1; p = 0.02) in the second model.

CONCLUSIONS

Low HDL-C (or high TC:HDL-C) is strongly predictive of subsequent cardiovascular events in subjects with CAD, despite desirable TC. As such, identification of this potentially modifiable risk factor should be actively pursued in this high-risk subgroup.

The genetic dyslipoproteinemias--nosology update 1990

The number of discrete disorders of lipid transport is growing. Concomitantly, the classification of the disorders is changing, from one based on altered concentrations of lipoproteins, to one based on current understanding of the genetics of the disorders and of lipoprotein biochemistry and physiology. Many disorders are now traceable to deficiencies of essential proteins such as apolipoproteins, enzymes, lipid transfer proteins and cellular receptors.