Cardiovascular features of homozygous familial hypercholesterolemia: analysis of 16 patients

Causes of death in patients with familial hypercholesterolemia

Five out of 15 homozygotes and 41 out of 527 heterozygotes of familial hypercholesterolemia (FH) died during the past 10 years. Sudden death or heart failure was the cause of death in each of the 5 deceased homozygotes. Twenty heterozygotes died of myocardial infarction, 9 of sudden death, and 1 died after AC bypass surgery. Thus, 30 heterozygotes (73.2%) died of coronary heart disease (CHD). The mean age of death was significantly younger in male heterozygotes (54 years) than in the females (68 years). Rate of death from CHD in heterozygotes was 11 times higher than in the general population in Japan. Rate of death from pancreas cancer in FH was significantly higher than in the general population. These results suggest that FH is highly associated with pancreas cancer as well as CHD.

Multiple flexor tendon xanthomas and contractures in the hands of a child with familial hypercholesterolemia

A 6-year-old girl with familial hypercholesterolemia had flexion contractures of the fingers due to tendon and joint xanthomas. This unique problem was corrected by the combination of local hand surgery and a portacaval shunt.

Metabolism of low-density lipoproteins by cultured hepatocytes from normal and homozygous familial hypercholesterolemic subjects

The profoundly elevated concentrations of low-density lipoproteins (LDL) present in homozygous familial hypercholesterolemia lead to symptomatic cardiovascular disease and death by early adulthood. Studies conducted in nonhepatic tissues demonstrated defective cellular recognition and metabolism of LDL in these patients. Since mammalian liver removes at least half of the LDL in the circulation, the metabolism of LDL by cultured hepatocytes isolated from familial hypercholesterolemic homozygotes was compared to hepatocytes from normal individuals. Fibroblast studies demonstrated that the familial hypercholesterolemic subjects studied were LDL receptor-negative (less than 1% normal receptor activity) and LDL receptor-defective (18% normal receptor activity). Cholesterol-depleted hepatocytes from normal subjects bound and internalized 125I-labeled LDL (Bmax = 2.2 micrograms LDL/mg cell protein). Preincubation of normal hepatocytes with 200 micrograms/ml LDL reduced binding and internalization by approx. 40%. In contrast, 125I-labeled LDL binding and internalization by receptor-negative familial hypercholesterolemic hepatocytes was unaffected by cholesterol loading and considerably lower than normal. This residual LDL uptake could not be ascribed to fluid phase endocytosis as determined by [14C]sucrose uptake. The residual LDL binding by familial hypercholesterolemia hepatocytes led to a small increase in hepatocyte cholesterol content which was relatively ineffective in reducing hepatocyte 3-hydroxy-3-methylglutaryl-CoA reductase activity. Receptor-defective familial hypercholesterolemia hepatocytes retained some degree of regulatable 125I-labeled LDL uptake, but LDL uptake did not lead to normal hepatocyte cholesterol content or 3-hydroxy-3-methylglutaryl-CoA reductase activity. These combined results indicate that the LDL receptor abnormality present in familial hypercholesterolemia fibroblasts reflects deranged hepatocyte LDL recognition and metabolism. In addition, a low-affinity, nonsaturable uptake process for LDL is present in human liver which does not efficiently modulate hepatocyte cholesterol content or synthesis.

Improved survival of patients with homozygous familial hypercholesterolaemia treated with plasma exchange

Plasma exchange was undertaken in five patients with homozygous familial hypercholesterolaemia at intervals of two weeks for a mean of 8.4 years. These patients had survived an average of 5.5 years longer than their five respective homozygous siblings (p = 0.3), each of whom must have had a matching genetic defect but who died untreated. The 37% decrease in peak serum cholesterol concentrations maintained by plasma exchange presumably reduced progression of atherosclerosis in the treated patients and thus lessened their risk of premature death.

Characterization of a human hepatic receptor for high density lipoproteins

Characterization of the membrane receptor for the low density lipoproteins (LDL) has led to insights into cellular receptor physiology as well as mammalian lipid transport. Result with LDL have stimulated the search for specific receptors for other plasma lipoproteins. Receptors for high density lipoproteins (HDL) have been identified in human fibroblasts and smooth muscle cells. Specificity for this receptor has been difficult to define since normal HDL contains several apolipoproteins, and particles containing apolipoproteins B and E have been shown to compete for HDL binding. In the present study, we demonstrate that HDL isolated from a patient devoid of apolipoprotein E was bound specifically by human hepatic membranes. This binding reached saturation within 2 hours and was EDTA-resistant. Assuming a single receptor model, we found that 2.9 x 10(15) receptors/mg membrane protein bound with an affinity KD = 3.5 x 10(-7) M at 0 to 4 degrees C and KD = 1.9 x 10(-7) M at 37 degrees C. The binding was effectively competed with intact HDL3, with HDL3 that had undergone selective arginine and lysine residue modification, and with antibodies to apolipoproteins A-I and A-II. However, LDL, asialofetuin, and HDL3 which had undergone tyrosine modification by nitration, and anti-apolipoprotein B did not compete with apo A-I HDL binding. In contrast to LDL binding, the human hepatoma cell line, HEPG2, increased HDL binding with cholesterol loading that was specific for HDL3. Thus, hepatic tissue can modulate its recognition of HDL. Finally, hepatic membranes from a patient lacking normal hepatic LDL receptors bound apo A-I HDL normally. These data indicate that a saturable, specific regulatable receptor for apo E-free HDL is present in human liver.

The association of LDL receptor activity, LDL cholesterol level, and clinical course in homozygous familial hypercholesterolemia

Patients with homozygous familial hypercholesterolemia (FH), reveal a marked heterogeneity in plasma cholesterol levels, response to diet as well as drug treatment, and clinical course. Low-density lipoprotein (LDL) receptor activities were assessed by the rate of 14C-oleate cholesteryl ester biosynthesis in fibroblasts from 13 FH homozygotes in tissue culture. The receptor activity of the individual patients was highly correlated with initial pretreatment plasma cholesterol and LDL cholesterol levels (P less than .001, r = -0.89). In addition, the LDL receptor activity was positively correlated with the age of onset of angina based on the Cox model (P less than .035, likelihood ratio = 6.71). An association was also noted between LDL receptor activity and cholesterol reduction with drugs. These data provide direct evidence for the correlation between the heterogeneity of the LDL receptor and the expression of the clinical manifestations of homozygous FH. The determination of pretreatment plasma cholesterol level and LDL receptor activity in patients with homozygous FH provide useful parameters on which to base predictions of the clinical progression of cardiovascular disease. These parameters may also influence the selection of a program for diet and drug therapy. Patients with markedly elevated plasma cholesterol levels and very low LDL receptor activity should be considered to be candidates for multiple drug therapy, and portacaval shunt, and/or periodic plasma exchanges.