Deletion of exon 15 of the LDL receptor gene is associated with a mild form of familial hypercholesterolemia. FH-Espoo.

We describe a mutation of the low-density lipoprotein (LDL) receptor gene, designated familial hypercholesterolemia (FH)-Espoo, which deletes exon 15 of the LDL receptor gene. The mutant receptor is predicted to lack 57 amino acids, including 18 serine and threonine residues, which are the sites of the clustered O-linked sugars of the receptor. Studies on 10 carriers of this gene revealed that FH-Espoo is associated with an exceptionally mild form of FH. Thus, in conditions in which cell proliferation was rendered dependent on the function of LDL receptors, lymphocytes from the patients with the FH-Espoo allele had a growth rate intermediate between those from healthy subjects and patients with the FH-Helsinki gene, a mutation known to abolish LDL receptor function. The in vivo fractional catabolic rate of LDL apolipoprotein B was lower than normal in the two FH-Espoo heterozygotes studied. Although higher than those in healthy controls, the serum LDL cholesterol concentrations in patients with the FH-Espoo gene were significantly lower than those in patients with the FH-Helsinki mutation. The thickness of the Achilles tendons was within the normal limits in subjects with the FH-Espoo gene. Our study suggests that moderate varieties of hypercholesterolemia, ie, those not considered to represent FH, may occasionally be due to subtle LDL receptor gene mutations.

Diagnosis of heterozygous familial hypercholesterolemia. DNA analysis complements clinical examination and analysis of serum lipid levels.

The concordance of clinical and molecular genetic diagnoses of heterozygous familial hypercholesterolemia (FH) was studied in 65 subjects (10 propositi and 55 first-degree relatives) from 10 families with FH. Nine propositi were carriers of the FH-Helsinki deletion of the low density lipoprotein (LDL) receptor gene, prevalent in the Finnish population, while a new deletion, extending from intron 14 to intron 15 of the LDL receptor gene, was identified in one family. Serum LDL cholesterol levels used in the clinical diagnosis (less than 5.0 mmol/l, not FH; 5.0-5.9 mmol/l, possible FH; greater than or equal to 6.0 mmol/l, FH; limits are 1 mmol/l lower for those less than 18 years) were derived from an authoritative recommendation. Tendon xanthomas constituted an additional criterion. With the DNA analysis as the reference, 55 (85%) subjects could be correctly classified clinically as FH patients or subjects without FH. The remaining 10 subjects were misclassified or were in the "possible FH" category. When the age- and sex-specific 95th percentile LDL cholesterol levels were used instead of the rigid values for both adults and children, the percentage of correct diagnoses rose to 95%. Common genetic polymorphisms of apolipoproteins E and B did not markedly affect LDL cholesterol levels in FH patients, whereas increasing age and obesity were associated with elevated LDL levels. In conclusion, DNA analysis is a valuable adjunct to the diagnosis of FH that is applicable to families with a known mutation of the LDL receptor gene. If DNA methods are not available, age- and sex-specific LDL levels should be used as an aid in the clinical diagnosis of FH.

Increased amounts of cholesterol precursors in lipoproteins after ileal exclusion.

Serum cholesterol precursor sterols reflect the activity of cholesterol synthesis. In this study, squalene, methyl sterol and lathosterol contents were studied in very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) of heterozygous familial hypercholesterolemia patients without and with ileal bypass. The contents of lathosterol and all methyl sterols (lanosterol, delta 8,24-dimethylsterol, delta 8-dimethylsterol, delta 8-methostenol and methostenol), but not of squalene were increased in all lipoproteins by ileal bypass. The increase in the free methyl sterols was more marked than that in the esterified ones. The percentage esterification of the methyl sterols was highest in HDL and lowest in VLDL. Lipoprotein methyl sterol contents were positively correlated with each other and with cholesterol synthesis. The methyl sterols were slightly concentrated in LDL, and squalene strongly concentrated in VLDL. It is concluded that long-term stimulation of cholesterol synthesis increases the methyl sterols in all lipoproteins.

The partial ileal bypass operation does not cause essential fatty acid deficiency.

Recent studies have indicated that ileal resection may lead to essential fatty acid deficiency, as demonstrated by plasma fatty acid composition. In the present study the serum cholesterol ester fatty acid composition was determined in patients who had undergone a partial ileal bypass operation several years earlier. The mean length of ileal exclusion was 2.0 m (range, 1.4-2.5 m). The patients with ileal bypass had severe bile acid malabsorption and slight fat malabsorption (fecal fat, 16 g/day). The fatty acid composition of serum cholesterol esters in the patients with ileal exclusion was identical with that of matched controls; for example, linoleic acid comprised 58% of the C14-18 fatty acids in the control patients and 61% in the patients with ileal bypass. It is concluded that exclusion of the distal third of a healthy small bowel does not cause essential fatty acid deficiency.

Evaluation of bile acid malabsorption by plasma cholesterol precursor sterols in familial hypercholesterolaemia patients with and without ileal exclusion.

To evaluate the value of plasma cholesterol precursor sterols in the detection of bile acid malabsorption we measured these sterols in 14 familial hypercholesterolaemia patients, seven with and seven without an ileal exclusion. In the operated subjects bile acid malabsorption had induced a 4.8-fold increase in cholesterol synthesis, accompanied by a 1.9-5.1-fold increase in the plasma content of the eight cholesterol precursor sterols studied. There was no overlap between the two groups in any of these sterols, when total and free sterols were considered, and only three of the esterified sterols overlapped. The tri- and dimethyl sterols were mostly unesterified, monomethyl sterols modestly esterified and the demethylated sterols, especially desmosterol, were mainly esterified. The plasma lathosterol content segregated most clearly the patients with bile acid malabsorption from the controls. The lowest lathosterol value of the operated patients was 2.5-fold higher than the highest value of the control patients. Because lathosterol is the most abundant of the plasma cholesterol precursor sterols and is relatively easy to quantitate, it is suggested that plasma lathosterol measurement can be used in the detection of bile acid malabsorption.

Biliary lathosterol and other cholesterol precursor sterols are increased in patients with ileal exclusion.

The human bile contains several noncholesterol sterols, of which the cholesterol precursor sterols are quantitatively the most important. Detailed data on factors that regulate the amount of these sterols in the bile have not been available. In this study the effect of chronic stimulation of cholesterol synthesis on biliary cholesterol precursor sterol content was evaluated by measuring these sterols in the bile and plasma of familial hypercholesterolemia patients with and without ileal exclusion. In the operated patients cholesterol synthesis was fivefold increased, and cholesterol precursor sterols comprised 7% of the biliary sterols, compared with 2% in the control patients. All eight biliary cholesterol precursor sterols measured were significantly increased in the operated patients, and the increase was similar to that of respective sterols in plasma. Hence, the biliary methyl sterols were increased 2 to 4 times, the lathosterols 5 times, but demosterol only 1.5 times. The proportion of lathosterol was higher and that of lanosterol lower in the bile of the operated than in that of the control patients. We conclude that activation of cholesterol synthesis increases the amount of cholesterol precursor sterols in the bile in proportion to the increase of these sterols in plasma and to the overall cholesterol synthesis.

Plasma and biliary cholestanol related to steroid metabolism in familial hypercholesterolemia patients with and without ileal exclusion.

Plasma cholestanol is increased in cerebrotendinous xanthomatosis and in sitosterolemia with xanthomatosis. We measured plasma and biliary cholestanol in heterozygous familial hypercholesterolemia patients with (n = 10) and without (n = 12) ileal exclusion. In the unoperated patients plasma cholestanol concentration (12.9 mumol/l) and content (1.2 mmol/mol cholesterol) were slightly higher than in the nonhypercholesterolemic control subjects studied by us. Ileal exclusion had lowered plasma cholestanol concentration but only in proportion to the lowering of plasma cholesterol concentration, and plasma cholestanol content (mmol/mol cholesterol) was similar in the operated and unoperated subjects. Plasma and biliary cholestanol contents were positively associated. In the unoperated patients the fractional cholesterol absorption and plasma plant sterols, also reflecting sterol absorption, were positively correlated with plasma cholestanol content. Our study suggests, that plasma cholestanol is slightly elevated in familial hypercholesterolemia and that, in addition to plasma lipoprotein level, sterol absorption is important in the regulation of plasma cholestanol level. Ileal exclusion decreases plasma cholestanol in proportion to the decrement in the plasma cholesterol concentration.

Effect of ileal exclusion on lipoprotein sitosterol in familial hypercholesterolaemia.

A plant sterol, sitosterol, was quantitated in very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) and related to faecal steroids and cholesterol absorption in heterozygous familial hypercholesterolaemia patients with (n = 7) and without ileal bypass (n = 6). The latter had resulted in severe bile acid malabsorption but fractional cholesterol absorption was within low control limits. Serum total and LDL cholesterol and apoprotein B levels were reduced, whereas HDL cholesterol, apoprotein A-I, VLDL and HDL sitosterol concentrations were increased by the ileal exclusion, and the increase in LDL and serum total sitosterol levels was insignificant. In terms of mmol/mol of cholesterol or apoprotein B, however, the LDL and total sitosterol contents were higher in the subjects who had undergone operation. For an unknown reason the sitosterol content increased gradually within the lipoprotein particles from the lighter to the heavier lipoproteins, and the enrichment was similar in the two groups. Dietary sitosterol intake, indicated by faecal sitosterol excretion, was similar in the two groups. The contents of serum total and LDL sitosterol were positively correlated with the dietary sitosterol intake in both groups, and with the fractional cholesterol absorption only in the group not subject to operation. These associations were less consistent for sitosterol contents in other lipoproteins. We conclude that normally the serum sitosterol content reflects cholesterol absorption efficiency even in patients with familial hypercholesterolaemia, provided the dietary sitosterol intake is quite constant. In addition, for unknown reasons ileal exclusion leads to an increased lipoprotein sitosterol content.

Peripheral arterial disease in heterozygous familial hypercholesterolemia: no difference between patients with and without partial ileal bypass.

We evaluated lower limb arterial circulation in 37 patients with heterozygous familial hypercholesterolemia using strain-gauge plethysmography. Nineteen patients were initially allocated to surgical therapy (ileal bypass operation), and 18 control patients were treated conservatively. After a follow-up period of 3-12 years (mean 10 yrs) the surgically treated patients had significantly lower serum total (9.4 vs. 11.9 mmol/l, P less than 0.001) and LDL (6.2 vs. 8.1 mmol/l, P less than 0.01) cholesterol and apoprotein B levels and higher HDL cholesterol (1.2 vs. 1.0 mmol/l, P less than 0.05) and apoprotein A-I levels compared with controls. There was no significant difference in the prevalence of intermittent claudication (16 vs. 6%) or coronary heart disease (68 vs. 61%) between the operated and control groups. The ankle-arm systolic blood pressure ratio was pathologically low in 53% of the operated and 72% of the control patients, and the toe-arm pressure ratio in 50% and 44%, respectively. These differences or the differences in the mean ankle-arm and toe-arm pressure ratios between the groups were not significant. The toe-ankle pressure gradient was normal in all but 2 patients indicating that atherosclerotic changes predominantly affect the more proximal arteries in familial hypercholesterolemia. Patients with peripheral arterial disease could not be differentiated by serum lipoprotein levels, blood pressure or the presence of coronary heart disease. However, smoking was more prevalent (38% vs. 0%, P less than 0.05) in patients with impaired peripheral circulation. We conclude that asymptomatic peripheral arterial disease is quite common in familial hypercholesterolemia, and that smoking increases its risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Fecal and biliary bile acid composition after partial ileal bypass operation.

Biliary and fecal bile acid composition was studied in 13 patients 3-12 years after a partial ileal bypass operation and in 10 unoperated controls, all with heterozygous familial hypercholesterolemia. Three operated patients were taking cholestyramine. The relative amount of cholic acid in the bile was decreased at the expense of chenodeoxycholic acid in the operated subjects. Chenodeoxycholic acid content of the bile correlated negatively with the fractional cholesterol absorption, suggesting that in compromised absorption chenodeoxycholic acid is absorbed more efficiently than cholic acid. Despite a ninefold increase in total bile acid synthesis the cholic/chenodeoxycholic acid synthesis ratio was not significantly different in the operated and control subjects. However, the lower the chenodeoxycholic acid synthesis the higher was the proportion of deoxycholic acid in the bile and feces, suggesting regulation of chenodeoxycholic acid synthesis by deoxycholic acid. Ileal exclusion had increased the proportion of primary bile acids in the feces from below 10 to over 50%. Despite increased fecal water excretion the concentration of fecal total and dihydroxy bile acids was higher in the operated than in control subjects. However, the fecal concentration of the potentially cancer-promoting bile acids, deoxycholic acid and lithocholic acid, was not increased in the operated subjects. In the operated subjects, fecal water output was positively correlated with total bile acid and chenodeoxycholic acid synthesis. It is concluded that the severe bile acid malabsorption caused by ileal exclusion activates the synthesis of both primary bile acids in similar amount. However, after ileal exclusion the relative amount of cholic acid in the bile is decreased, obviously because loss of ileal absorption predominantly affects the absorption of cholic acid.

Effect of ileal exclusion on plant sterol metabolism in familial hypercholesterolemia.

Factors regulating the metabolism of plant sterols (sitosterol and campesterol) and their serum levels were studied in sixteen patients with heterozygous familial hypercholesterolemia. Eight patients had undergone an ileal bypass operation, resulting in slight fat and severe bile acid malabsorption and in lowered serum cholesterol concentration, but normal fractional cholesterol absorption. Serum plant sterol concentrations (mg/dl) were similar in the two groups, but expressed per milligram of cholesterol were higher in the operated patients. Fecal excretion (equal with intake) and biliary secretion (reflecting absorption) of the plant sterols were similar in the two groups and were significantly correlated with the serum plant sterol content, which also correlated positively with the fractional cholesterol absorption in the control but not in the operated group. The estimated fractional absorption of the plant sterols was similar in the two groups, but that of sitosterol (3.5%) was lower than that of campesterol (9.1%). Our study shows that serum plant sterols are associated with fractional cholesterol absorption even in patients with familial hypercholesterolemia. However, after ileal exclusion dietary intake of the plant sterols is the main regulator of their serum levels.

Effect of ileal exclusion on kinetics of very low density lipoprotein triglycerides in familial hypercholesterolemia.

Plasma lipoproteins, VLDL triglyceride kinetics, and bile acid and cholesterol synthesis were measured in 21 patients heterozygous for familial hypercholesterolemia with (n = 11) or without (n = 10) ileal bypass. LDL cholesterol and apoprotein B concentrations were lower, and cholesterol and bile acid synthesis, the VLDL triglyceride/cholesterol ratio, and the HDL cholesterol concentration were higher in the operated than the control patients. The VLDL triglyceride production rate was increased in the operated normotriglyceridemic patients by about 65%, whereas the fractional catabolism of VLDL triglycerides and the calculated VLDL cholesterol transport were similar in the operated and control groups. VLDL triglyceride production was not correlated with cholesterol or bile acid synthesis. The VLDL triglyceride concentration was positively correlated with the production and negatively with the fractional catabolism of VLDL triglycerides. In unoperated normotriglyceridemic patients the VLDL triglyceride production was positively correlated with LDL cholesterol (r = 0.69, p less than 0.05), LDL triglyceride (r = 0.84, p less than 0.01) and LDL apoprotein B (r = 0.80, p less than 0.01) concentrations, and with the LDL triglyceride/apoprotein B (r = 0.72, p less than 0.05) and LDL triglyceride/cholesterol (r = 0.68, p less than 0.05) ratios. None of these correlations was significant in the operated patients. We conclude that in heterozygous familial hypercholesterolemia VLDL triglyceride level depends on both VLDL triglyceride synthesis and catabolism, LDL level is proportionate to VLDL triglyceride production in the unoperated patients but not in the patients with ileal bypass, ileal exclusion results in an increase in the production rate of VLDL triglycerides in normotriglyceridemic patients but otherwise VLDL triglyceride production is poorly associated with cholesterol and bile acid synthesis, ileal exclusion may induce hepatic secretion of triglyceride-rich VLDL.