Familial occurrence of mild hyperlipoproteinaemias

Cholesterol absorption and lipoprotein metabolism in type II diabetes mellitus with and without coronary artery disease

Hypercholesterolemia is an important atherogenic risk factor in type II diabetes, and although coronary artery disease (CAD) is frequent in these patients, it is not known whether cholesterol and lipoprotein metabolism differ in patients with (CAD+) and without CAD (CAD-). Our aim was to study cholesterol metabolism and lipoprotein kinetics in mildly hypercholesterolemic type II diabetic men with and without CAD under similar dietary conditions. Despite similar serum and lipoprotein cholesterol levels, and kinetics of total and dense LDL apo B, light and dense LDL particles were cholesterol-enriched only in CAD+ subjects. Apolipoprotein A-II level was lower in CAD+ than in CAD- subjects (27.1 +/- 0.7 versus 30.9 +/- 0.7 mg/dl, P < 0.05), HDL cholesterol and apolipoprotein A-I kinetics were similar in the two groups. Cholesterol absorption was significantly higher in the CAD+ versus CAD- subjects (27 +/- 2 versus 20 +/- 3%, P < 0.05). In multiple logistic stepwise regression analysis with CAD as the dependent variable, cholesterol absorption efficiency and serum plant sterol/cholesterol proportions were the only variables significantly associated with CAD. In conclusion, in mildly hypercholesterolemic type II diabetic patients, the only metabolic parameter differentiating CAD patients from non-CAD ones was significantly higher cholesterol absorption efficiency in the coronary patients, which could contribute to the finding of the atherogenic cholesterol-rich dense LDL subfraction in these patients. Thus, a treatment causing cholesterol malabsorption by sitostanol alone or in combination with statin could be beneficial in these patients.

Serum low density lipoprotein cholesterol level and cholesterol absorption efficiency are influenced by apolipoprotein B and E polymorphism and by the FH-Helsinki mutation of the low density lipoprotein receptor gene in familial hypercholesterolemia

The aim of the present study was to evaluate the effect of variation of different gene loci separately and in concert on lipid metabolism in heterozygous familial hypercholesterolemia (FH). We assayed a unique low density lipoprotein (LDL) receptor gene defect (designated as FH-Helsinki), the XbaI polymorphism of the apolipoprotein (apo) B, phenotypes of the apo E, and determined the levels of serum lipoproteins, the efficiency of cholesterol absorption, and the values for several parameters of cholesterol metabolism in 51 unrelated patients with heterozygous FH. The genetic parameters were distributed independently of each other. Gender distribution and the prevalence of coronary artery disease were similar in the different apo E phenotypes, in the apo B genotypes, and in patients with and without the FH-Helsinki mutation. However, the FH-Helsinki mutation was associated with an increased body mass index. Serum LDL cholesterol was significantly elevated in patients with the FH-Helsinki mutation and the apo B X2 allele. Apo E phenotypes were not related to serum lipids per se, but the highest serum LDL cholesterol levels were measured in patients with the FH-Helsinki gene, apo E4 phenotype, and at least one X2 allele. Patients with the FH-Helsinki mutation and apo E4 phenotype had the highest cholesterol absorption efficiency. Cholesterol absorption was not related to serum lipids or lipoproteins, but LDL cholesterol was most elevated in patients with the most efficient cholesterol absorption. We conclude that in FH, diverse genetic factors exert individual and additive influences on serum LDL cholesterol levels.

Relationship of branched-chain alpha-keto-acids and lipids in sera of hypertriglyceridemic subjects

According to the present study, in hyperlipidemias where triglyceride values in serum are raised, the triglyceride values are associated with increased amounts of branched-chain alpha-keto-acids (BCKA) in the serum. In particular, the concentration of alpha-ketoisocaproic acid (KICA), which in the control sera was 34.4 mumol/l, was in type IIB hyperlipidemia 40.4% and in type IV 49.4% higher than in controls with normal serum lipid values. In type IV hyperlipidemia, values for alpha-ketoisovaleric acid (KIVA) and alpha-keto-beta-methyl-n-valeric acid (KMVA) were also high when compared to the corresponding mean values of the controls, 7.1 and 18.8 mumol/l. The respective differences were 57.7 and 44.1 per cent. In type IIB hyperlipidemia, KIVA was significantly and KMVA insignificantly increased compared to the control group. In type IIA hyperlipidemia with normal triglyceride values, none of the three BCKA differed significantly from the controls. These results also indicate that the increased amounts of individual BCKA somehow depend on the concentration of triglycerides in serum, while no relationship was found between BCKA values and cholesterol concentration.

Coronary artery disease and bile acid synthesis in familial hypercholesterolemia

A cohort of 97 consecutive patients (mean age 43 years), heterozygous for familial hypercholesterolemia (FH) with tendon xanthomata, were studied to explore the possible association of coronary artery disease (CAD) with classical risk factors of CAD and parameters of cholesterol metabolism, including cholesterol and bile acid synthesis. Seventy percent of the patients had CAD. Male sex, advanced age (in females), increased blood pressure (in females), obesity (in males), short stature and clinical signs of tissue deposition of cholesterol were more common in the patients with than without CAD. Serum total and LDL-cholesterol and triglyceride levels were not associated with the presence of CAD. As compared with normolipidemic healthy subjects, studied under similar conditions, the bile acid synthesis was subnormal in FH. However, the low bile acid values were associated with CAD, especially in men, while the bile acid formation was within the normal limits in the healthy FH patients. The findings suggest that FH patients with a low bile acid synthesis have an increased risk to develop coronary heart disease by an unknown mechanism.

Familial combined hyperlipoproteinemia. Evidence for a role of growth hormone deficiency in effecting its manifestation

Hyperlipidemia associated with an isolated deficiency of growth hormone was investigated in 10 subjects with hypercholesterolemia consistently present over a 10-yr period. 8 of these 10 had serum triglyceride concentrations greater than 185 mg/dl. 13 growth hormone-deficient patients with normal serum lipids, 28 age-matched controls, and 6 families possessing both growth hormone-deficient and hormonally normal members were also studied. Hyperlipidemia occurred with growth hormone deficiency only in families in which hormonally normal subjects likewise exhibited hyperlipidemia. However the elevation of serum lipids, particularly cholesterol, was invariably greater in the growth hormone-deficient members of these families. Studies were most consistent with the classification of this trait as familial combined hyperlipoproteinemia. Basal serum concentrations of insulin, glucose, and free fatty acids were similar in all groups. After oral glucose (1.5 g/kg of body wt) both hyperlipidemic and normolipidemic dwarfs exhibited a similar degree of glucose intolerance associated with insulinopenia. Sensitivity to insulin, assessed after the intravenous injection of insulin (0.05 U/kg of body wt), increased and was virtually identical in the two dwarf groups. Administration of 5 mg of human growth hormone twice a day for 1 wk to five subjects did not alter serum lipid patterns. The data provide no conclusive evidence concerning a direct effect of growth hormone deficiency on hyperlipoproteinemia. We postulate that in some individuals growth hormone deficiency may unmask an underlying defect in lipoprotein metabolism.

Myocardial infarction in the familial forms of hypertriglyceridemia

Among 74 hypertriglyceridemic patients who were referred for study because of hypertriglyceridemia, family investigations detected 19 with familial hypertriglyceridemia and 24 with familial combined hyperlipidemia. The frequency of myocardial infarction among adult living hyperlipidemic relatives of patients with familial combined hyperlipidemia was 17.5% (10/57). Five of these relatives had their infarct between the ages of 40 and 50 yr of age, and five before the age of 40 yr. The frequency of myocardial infarction in living hyperlipedemic relatives with familial hypertriglyceridemia was 4.7% (2/43) and was similar to the frequency of myocardial infarction among normolipidemic relatives (4.5%) or among spouse controls (5.2%). Mortality data due to myocardial infarction among relatives of index patients failed to contribute meaningful information.

The heritable hyperlipoproteinemias and atherosclerosis

1. The genetic hyperlipoproteinemias are common, are easily diagnosed and are often expressed in children or in infants. 2. Familial combined hyperlipidemia, hypercholesterolemia and hypertriglyceridemia are all associated with a markedly augmented atherosclerotic cardiovascular event rate. 3. The clinical importance of early diagnosis, family screening, and lipid sampling in high risk or free living populations must be emphasized. 4. Exciting progress at a biochemical molecular level (in tissue culture, for example) provides better understanding of the genetic hyperlipoproteinemias and possible avenues for its better therapy.